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Cold tolerance and plant growth promotion potential of Serratia marcescens strain SRM (MTCC 8708) isolated from flowers of summer squash (Cucurbita pepo)
Abstract
To determine the cold tolerance and plant growth promotion potential of Serratia marcescens strain SRM (MTCC 8708).
Serratia marcescens strain SRM was isolated from the flowers of summer squash plants, showing no apparent symptoms of yellow vine disease. It was evaluated for growth and plant growth promotion attributes at 15 and 4 degrees C. At 15 degrees C, the isolate was able to solubilize 76.6 microg ml(-1) of P and produce Indole Acetic Acid, IAA (11.1 microg ml(-1)). HCN and siderophore production were also detected at 15 degrees C. The isolate retained all the plant growth promotion traits at 4 degrees C. Seed bacterization with the isolate significantly enhanced plant biomass and nutrient uptake of wheat seedlings grown in cold temperatures.
Serratia marcescens strain SRM is a promising cold-tolerant isolate that can significantly influence wheat seedling growth at cold temperatures.
This strain can be employed as a bioinoculant in cold temperature conditions.
Supplementary resource (1)
Nucleotide Sequence
May 2007
... Drought alters the osmotic balance, pigmentation, membrane stability, and photosynthetic activity to negatively affect plant health. Drought also affects plants' ability to absorb and translocate essential elements and leads to oxidative stresses (Seleiman et al., 2021). The effect of drought stress ranges from moderate and short to extremely severe and prolonged duration. ...
... Coping with drought stress, plants employ various adaptations and mitigation strategies, which differ with various species. They initiate a series of physiological and biochemical responses to reduce water loss through the closure of stomata (alteration in stomatal conductance and distribution), hormonal regulation (abscisic acid accumulation), photosynthetic rate reduction, the expression of aquaporins and vacuolar H + -pyrophosphatases for maintaining cell turgor through osmotic adjustments, root length increase, the enhancement in transpiration efficiency, the accumulation of compatible osmolytes, and oxidoreductase enzymes, which result in cell integrity, functionality and survival of plants (Seleiman et al., 2021;Yang et al., 2021). Drought stress also alters the activity and functional composition of soil microorganisms that are responsible for crucial ecosystem functions and services. ...
... These bacteria also have PGP abilities including phosphorus and zinc solubilization, N 2 fixation, siderophore and plant hormone production that facilitate nutrient uptake and cold tolerance in plants (Verma et al. 2015). PGPB can help to withstand cold stress by inducing antioxidant, hormonal, photosynthetic and other stress related pathways in plants (Bashan et al., 2004;Selvakumar et al., 2008;Tiwari et al., 2017). In particular, Bacillus spp. ...
Environmental (abiotic) stresses significantly threaten the worldwide crop production and food security. Rapid, drastic changes in the global climate have exacerbated such stresses for crops. Plant-associated bacteria have been shown to enhance stress resistance and cope with the negative impacts of various abiotic stresses through the induction of various mechanisms. In soil, the rhizosphere and endosphere of plants, the Bacillus genus is a predominant bacterial genus. Members of this genus, which are tremendously diverse both metabolically and genetically, survive for a long time under unfavorable environmental conditions due to their ability to form long-lived, stress-tolerant spores. Bacillus spp. secrete several metabolites that trigger plant growth and enhance plants’ tolerance to biotic and abiotic stresses. Some of the Bacillus species are available commercially as phytostimulants, biopesticides, and biofertilizers. Due to this functional versatility, the Bacillus genus is one of the most widely used in the agro-biotech industry. However, the potential of the Bacillus genus has not yet been sufficiently realized, and transferring technology related to the genus from the lab environment to real world applications in the field needs to be emphasized. A better understanding of mechanisms of action of beneficial Bacillus spp. is needed for the development of products to support green biotechnology in agriculture and industries. This report comprehensively reviews the applications of Bacillus spp. in abiotic (e.g., salinity, drought, inorganic and organic pollutant toxicity, nutritional imbalance, low-high temperatures, and waterlogging) -stressed agriculture and discusses their potentials for the development of new products of biotechnological implications, highlighting gaps that remain to be explored to improve and expand on Bacillus-based biostimulants.
... The pH reduction observed in the in vitro phosphate solubilization assay (Table 1), coupled with the identification of multiple genes involved in gluconic acid synthesis (Silva et al., 2021), indicates that MBSA-MJ1 could be producing organic acids as a mechanism to solubilize phosphate (Rodríguez et al., 2006). This mechanism for phosphate solubilization has been previously reported in Serratia marcescens strains (Chen et al., 2006;Selvakumar et al., 2008;Ben Farhat et al., 2009). Impatiens and pansy plants treated with MBSA-MJ1 also had significantly greater tissue potassium concentration than the uninoculated control ( Figure 3C). ...
... Impatiens and pansy plants treated with MBSA-MJ1 also had significantly greater tissue potassium concentration than the uninoculated control ( Figure 3C). Application of Serratia marcescens strains NBRI1213 and MTCC 8708 similarly show increases of phosphorus and potassium tissue nutrient content in maize and wheat plants (Selvakumar et al., 2008;Lavania and Nautiyal, 2013). Our in vitro characterization showed a similar decrease in media pH and increase in soluble potassium in defined media when inoculated with MBSA-MJ1 (Table 1); therefore, it is probable that MBSA-MJ1 is able to utilize organic acid production as a mechanism to solubilize and increase the bioavailability of potassium similar to phosphate (Sharma et al., 2016). ...
High fertilizer rates are often applied to horticulture crop production systems to produce high quality crops with minimal time in production. Much of the nutrients applied in fertilizers are not taken up by the plant and are leached out of the containers during regular irrigation. The application of plant growth promoting rhizobacteria (PGPR) can increase the availability and uptake of essential nutrients by plants, thereby reducing nutrient leaching and environmental contamination. Identification of PGPR can contribute to the formulation of biostimulant products for use in commercial greenhouse production. Here, we have identified Serratia plymuthica MBSA-MJ1 as a PGPR that can promote the growth of containerized horticulture crops grown with low fertilizer inputs. MBSA-MJ1 was applied weekly as a media drench to Petunia × hybrida (petunia), Impatiens walleriana (impatiens), and Viola × wittrockiana (pansy). Plant growth, quality, and tissue nutrient concentration were evaluated 8weeks after transplant. Application of MBSA-MJ1 increased the shoot biomass of all three species and increased the flower number of impatiens. Bacteria application also increased the concentration of certain essential nutrients in the shoots of different plant species. In vitro and genomic characterization identified multiple putative mechanisms that are likely contributing to the strain’s ability to increase the availability and uptake of these nutrients by plants. This work provides insight into the interconnectedness of beneficial PGPR mechanisms and how these bacteria can be utilized as potential biostimulants for sustainable crop production with reduced chemical fertilizer inputs.
... Traditional agricultural practices such as irrigation and smoke are not sufficient to protect this crop from frost exposure. Some experimental reports have indicated the positive results of plant growth promoting bacteria (PGPB) on the cold resistance/ cold alleviation in plants ( Barka et al. 2006;Mishra et al. 2009Mishra et al. , 2011Selvakumar et al. 2008;Subramanian et al. 2015;Theocharis et al. 2012a;Turan et al. 2013). Under stress conditions, PGPB are well recognized to improve the growth and productivity of agricultural crops (Nabti et al. 2010). ...
... Our study showed that Th+Fd-2 inoculation-induced amelioration of cold stress in plants was directly linked with efficient nutrient uptake over the control. It has been reported that Serratia marcescens was found effective in improving biomass and nutrient uptake in wheat seedlings, reducing the impact of cold stress (Selvakumar et al. 2008). Other studies also support that the plant's nutrient content increase can reduce frost injury of plants (Olgun et al. 2005;Taulavuori et al. 2005). ...
Cold stress in Ocimum sanctum is a major constraint to crop productivity in certain geographical regions. The current study was carried out to examine the effect of consortia of ACC deaminase producing microbes in reducing cold-induced damage in O. sanctum during winters to enable farmers to have O. sanctum as multi-cut crop. The effect of single and combined inoculation of ACC-deaminase producing four plant growth promoting bacteria (PGPB) including Brevibacterium halotoler-ans (Sd-6), Bacillus subtilis (Ldr-2), Achromobacter xylosoxidans (Fd-2) and Burkholderia cepacia (Art-7), and a biocontrol agent Trichoderma harzianum (Th) have been investigated. Inoculation of O. sanctum plant with Th+Fd-2 showed better photosynthetic efficiency, which could have resulted in enhanced fresh herb weight (83.78%), compared to un-inoculated control plants. Moreover, the inoculation of Th +Fd-2 improved the nutrient uptake, increased the accumulation of proline, starch, total phenolics, and reduced the accumulation of ACC (1-aminocyclopropane-1-carboxylic acid), a direct precursor for ethylene biosynthesis. Scanning electron microscopy showed the effective co-colonization of Th with Fd-2 on the root surface. Our results suggest that co-inoculation of Th+Fd-2 could be a green initiative that can improve plant growth and alleviate cold stress-induced damages in O. sanctum.
... Besides its human and economic aspect, S. marcescens is important from mycological and ecological point of view because lot of publications report this bacterium on fungi. According to research, S. marcescens can destroy the hypha (31,32,33), its activity does not decrease in cold weather (34). It was supported by our observations, too. ...
Background and purpose: The main objective of this paper is to report the occurrence of Serratia marcescens (Bizio, 1823), a bacterium on macrofungi and review the data of other collectors in Hungary. Materials and methods: Our mycological research was conducted in ten localities of the North Hungarian Mountain Ranges and in one sampling site of Mezőföld between 2019-2022. Results: Infection of S. marcescens was recorded on fourteen fungal species in northern Hungary. In addition, we reported 18 occurrence data of this bacterium by other collectors of Hungary. The infection of S. marcescens was highest in autumn. The most abundant infected fungal species was the edible and marketable Lepista personata (Fr.) Cooke, 1871. We identified the most fungal species as substrate in the family Agaricaceae. Conclusions: We conclude that the infection of S. marcescens of macrofungi was detected independently of life mode and habitat occupied of fungi. However, the seasons influenced the occupancy of this species to varying degrees.
... Different plant associated roles have been put forward for Serratiamarcescens, including that of a herbicide degradation bacterium [3] a plant growth promoting rhizobacterium [4]. Although S. marcescensis a conditional pathogenic bacterium that is capable of causing disease in diverse organisms, including humans [5] corals [6], insects [7], and plants [8], it is also a very important industrial strain which has been applied in fermentation for the production of various enzymes [9,10,11]. ...
Serratia bacterium was isolated from the compost samples and it was identified as Serratia sp., based on microscopic and biochemical characteristics. For molecular identification using specific PCR, the chromosomal DNA was extracted from the purified isolate and the DNA was subjected to amplification of the 16S r RNA gene. The PCR product was about 1200bp, the obtained amplicone was sequenced. The sequence analysis revealed that the isolate belongs to S. marcescens isolates with similarity 95%. The DNA sequence was deposited in gene bank under accession number of KP 797836 and the strain was labeled as SerratiamarcescensFek 323. The phylogentic analysis showed that our isolate is more closely related to chinease S. marcescens strain.
... [3] In the context of hill agriculture, psychrotrophic microbial inoculants are required as a major part of the crop season is characterized by cold. [4] In the present study, an attempt has been of the present study is to isolate psychrotrophic rhizobacteria from rhizosphere of Aconitum heterophyllum and to evaluate its growth promoting traits to select and develop more efficient indigenous plant growth promoting and disease suppressing bioagents for cold loving crops. ...
... In agreement with previous studies, the obtained bacterial isolates showed the ability to solubilize phosphate. High phosphate solubilization activity by Serratia sp. was reported by previous studies [48][49][50] that supported observation that gave Serratia isolates higher grade of phosphate solubilization compared with Bacillus isolates. The isolation of B2 Serratia SK3 as endophyte from cultivated root and B5 Serratia SK1a from the rhizospere of the wild oregano supports that it might be associated with the plant to enhance phosphate uptake. ...
... Phytohormones synthesis. The microbial production of individual phytohormones such as auxins and cytokinins has been well studied (Selvakumar et al., 2008;Spaepen et al., 2007). ...
... Inoculation of T. aestivum with Serratia marcescens enhanced plant growth and nutrient uptake (P, N, and K) in low temperatures. The ability of tested bacteria to solubilize P decreased at low temperatures [299]. ...
In the face of climate change, progressive degradation of the environment, including agricultural land negatively affecting plant growth and development, endangers plant productivity. Seeking efficient and sustainable agricultural techniques to replace agricultural chemicals is one of the most important challenges nowadays. The use of plant growth-promoting microorganisms is among the most promising approaches; however, molecular mechanisms underneath plant–microbe interactions are still poorly understood. In this review, we summarized the knowledge on plant–microbe interactions, highlighting the role of microbial and plant proteins and metabolites in the formation of symbiotic relationships. This review covers rhizosphere and phyllosphere microbiomes, the role of root exudates in plant–microorganism interactions, the functioning of the plant’s immune system during the plant–microorganism interactions. We also emphasized the possible role of the stringent response and the evolutionarily conserved mechanism during the established interaction between plants and microorganisms. As a case study, we discussed fungi belonging to the genus Trichoderma. Our review aims to summarize the existing knowledge about plant–microorganism interactions and to highlight molecular pathways that need further investigation.
... Many strains of the bacterium are known to be saprophytic in soil (Nawani and Kapadnis 2001) or endophytic in plants (Gyaneshwar 2001), but some are notorious for causing diseases on plants (Bruton et al. 1995(Bruton et al. , 2003Lukezic et al. 1982;Sears et al. 1975;Wang et al. 2015) and animals (Quesenberry and Short 1983) as well as on humans (Whalen 1970;Zipper et al. 1996). Several studies have been focused on the beneficial functions of some S. marcescens strains, such as biodegradation and bioremediation potential of environmental pollutants (Abo-Amer 2011;Cycoń et al. 2012); as a bio-collector for hematite flotation (Yang et al. 2014a, b); plant-growth-promoting potential (George et al. 2013;Lavania et al. 2006;Selvakumar et al. 2008); the biocontrol of insect pests (Deng et al. 2008;Fu et al. 2021;King et al. 1975;Podgwaite and Cosenza 1976;Qi et al. 2004;Sikorowski et al. 2001;Wang et al. 2010;Yang et al. 2014a, b;Zhao et al. 2017;Zhang et al. 2011Zhang et al. , 2021, plant pathogens (Ahmed 2010;Dong et al. 2016;Feng et al. 2018;Someya et al. 2001), plant diseases (Ordentlich et al. 1987 and1988;Someya et al. 2000;Wei et al. 1996) and weeds (Yang et al. 2015a, b;Li et al. 2021). ...
The Gram-negative rod-shaped bacterium Serratia marcescens is an opportunistic pathogen of many organisms, including insects. We report the identification and optimal in vitro chitinase production conditions of a novel chitinolytic S. marcescens strain TC-1 isolated from a naturally infected white grub ( Anomala corpulenta ) collected from a peanut field at Nanyang city, Henan province, China. Strain identification was conducted by morphological, physiological, biochemical and molecular analyses. The amplified 16S rRNA gene of TC-1 showed a similarity greater than 99% with multiple strains of S. marcescens . Based on Neighbor-joining phylogenetic tree analysis of bacterial 16S rRNA gene sequences, TC-1 formed a clade with S. marcescens , clearly separated from other Serratia spp. The strain TC-1 showed larvicidal activities against five insect species ( A. corpulenta , Plutella xylostella , Spodoptera exigua , Helicoverpa armigera , Bombyx mori ) and the nematode Caenorhabditis elegans , but not against S. litura . The operating parameters of chitinase production by TC-1 were optimized by response surface methodology using a three-factor, three-level Box-Behnken experimental design. The effects of three independent variables i.e. colloidal chitin concentration (7–13 g l ⁻¹ ), incubation time (24–72 h) and incubation temperature (24–32 °C) on chitinase production by TC-1 were investigated. A regression model was proposed to correlate the independent variables for an optimal chitinase activity predicted as 20.946 U ml ⁻¹ , using a combination of colloidal chitin concentration, incubation time and incubation temperature of 9.06 g l ⁻¹ , 63.83 h and 28.12 °C, respectively. The latter agreed well with a mean chitinase activity of 20.761 ± 0.102 U ml ⁻¹ measured in the culture supernatants of TC-1 grown under similar conditions with a colloidal chitin concentration, incubation time and incubation temperature of 9 g l ⁻¹ , 64 h and 28 °C, respectively. Our study revealed the S. marcescens strain TC-1 with potential as a biocontrol agent of insect pests and nematodes and demonstrated the proposed regression model's potential to guide chitinase production by this strain.
... Solanum lycopercsicum plants inoculated with OB155 strain of Pseudomonas vancoverensis and OS 261 strain of P. frederiks bergensis under low temperature conditions showed enhanced expression of genes related with cold acclimation and antioxidant activity in leaf parts of plants (Subramanian et al., 2015). It was observed that cold SRM strain of Serratia marcescens was found efficient in reducing cold stress injury due to induction of plants with cold tolerance ability (Selvakumar et al., 2008). Barka and coworkers (2006) investigated that seed treatment with PGPR has an intial effect on plants shoot as well as root growth by modifying the plant hormones including gibberlins, that play an essential role in seed germination. ...
... Solanum lycopercsicum plants inoculated with OB155 strain of Pseudomonas vancoverensis and OS 261 strain of P. frederiks bergensis under low temperature conditions showed enhanced expression of genes related with cold acclimation and antioxidant activity in leaf parts of plants (Subramanian et al., 2015). It was observed that cold SRM strain of Serratia marcescens was found efficient in reducing cold stress injury due to induction of plants with cold tolerance ability (Selvakumar et al., 2008). Barka and coworkers (2006) investigated that seed treatment with PGPR has an intial effect on plants shoot as well as root growth by modifying the plant hormones including gibberlins, that play an essential role in seed germination. ...
... So far, several cold-active bacterial strains with plant growth promotion properties have been described, e.g. Pantoea dispersa and Serratia marcescens, which were able to promote wheat growth even at 5°C (Selvakumar et al., 2008a;Selvakumar et al., 2008b). However, nowadays, novel nature-based solutions for agriculture are still needed; thus, scientists are constantly searching for novel candidates for biofertilizers. ...
Iron is the fourth most abundant element on earth. However, its low bioavailability is a key plant-growth limiting factor. Bacteria play an important role in plant growth promotion since they produce specific secondary metabolites that may increase macro- and micronutrient accessibility in soil. Therefore, bacterial-derived iron chelators, as well as surface-active compounds, are recognised as essential to plant welfare. In this study, three cold-active Antarctic bacterial strains, i.e. Pseudomonas sp. ANT_H12B, Psychrobacter sp. ANT_H59 and Bacillus sp. ANT_WA51, were analysed. The physiological and genomic characterisation of these strains revealed their potential for plant growth promotion, reflected in the production of various biomolecules, including biosurfactants (that may lower the medium surface tension of even up to 53%) and siderophores (including ANT_H12B-produced mixed-type siderophore that demonstrated the highest production, reaching the concentration of up to 1.065 mM), increasing the availability of nutrients in the environment and neutralising fungal pathogens. Tested bacteria demonstrated an ability to promote the growth of a model plant, alfalfa, increasing shoots’ length and fresh biomass even up to 26 and 46% respectively; while their metabolites increased the bioavailability of iron in soil up to 40%. It was also revealed that the introduced strains did not disrupt physicochemical conditions and indigenous soil microbial composition, which suggests that they are promising amendments preserving the natural biodiversity of soil and increasing its fertility.
... Besides, MSs encourage plant development by increasing the decomposition of organic matter and nutrient uptake in the soil and additionally suppress the negative effect of phytopathogens (Nihorimbere et al., 2011;Mishra et al., 2016). On the other hand, it has been demonstrated in many studies that MSs tolerate abiotic stress conditions and reduces yield losses (Calvo et al., 2014;Ipek et al., 2019;Selvakumar et al., 2008;Wang et al., 2012a;Yıldırım et al., 2006). ...
Cashmere production offers a new source of income for remote farmers in Central Asia where goats have long been raised. Between 2008-2018 we established a selected breeding flock to preserve, assess and improve the economic and genetic potential of cashmere-bearing indigenous goats in Kyrgyzstan. Significant effects of year, age and the sex of goats affected cashmere weight, while year and age of goat affected cashmere length and year affected cashmere fiber diameter. The best statistical model explained about 60% of the variation in both cashmere weight and length and about 30% of the variation in fiber diameter. No particular measurement year trend could be detected for any trait. Between years, cashmere weight varied between 103-150 g, fiber diameter between 15.8-17.6 m and length between 32-48 mm. Key words:Coat color, Indigenous goats, Fiber diameter, Fiber length, Genetic improvement
... This is even higher than the known cold-tolerant PGP strain Pseudomonas sp. strain PGERs17 from the Himalaya region of India, which was found to produce only 1.4 µg/mL at 4 • C [22], or Pantoea dispersa 1A and Serratia marcescens SRM from the northwestern Indian Himalayas, which were found to produce 3.0 µg/mL and 8.1 µg/mL, respectively [41]. ...
Agents of biological control are an important part of traditional agriculture, as well as organic farming. However, in the climatic conditions of countries that are located in cold and temperate regions, plant protection requires particular biocontrol agents that have adapted to environments with low and unstable temperatures. This work presents the biocontrol potential and plant-promoting activity of Bacillus spp. that was isolated from permafrost sediments in Western Siberia. It was found that all of the studied strains (n = 10) were able to produce indole-3-acetic acid (IAA) and chitinolytic enzymes at low positive temperatures (5 ◦C). The antifungal activity of cold-tolerant bacilli against Microdochium sp., Fusarium spp., and Alternaria sp was recorded. In greenhouse and field conditions, the selected strains (B. simplex 948 P1 (IAA-producing) and B. megaterium 312 (with antifungal
activity)) were assessed in comparison to a commercially available fungicide (tebuconazole) and biofungicide (B. subtilis 26D). It was found that the bacilli in the seed germination assay exhibited low phytotoxicity and there was no significant advantage over the conventional fungicides in the yield stimulation assay. However, the twin consortia of B. megaterium 312 and B. subtilis 26D was able to increase winter wheat yields by 50% (compared to the untreated group), and by 70% (compared to the commercial biofungicide-treated group). Moreover, applying the twin consortia of Bacillus spp. significantly reduced the infection rate of Fusarium spp. in first-generation wheat grain.
... Production of HCN by Pseudomonas fluorescens CHA0 has been observed to suppress black root rot of tobacco and root-knot nematode, Meloidogyne javanica in tomato [264,265]. Exiguobacterium acetylicum and Serratia marcescens have been reported as HCN producers from the north-western Indian Himalayas [266,267]. In addition to HCN, certain strains of PGP microbiomes are also ammonia producers. ...
The Himalayas are one of the most mystical, yet least studied terrains of the world. One of Earth's greatest multifaceted and diverse montane ecosystems is also one of the thirty-four global biodiversity hotspots of the world. These are supposed to have been uplifted about 60-70 million years ago and support, distinct environments, physiography, a variety of orogeny, and great biological diversity (plants, animals, and microbes). Microbes are the pioneer colonizer of the Himalayas that are involved in various bio-geological cycles and play various significant roles. The applications of Himalayan microbiomes inhabiting in lesser to greater Himalayas have been recognized. The researchers explored the applications of indigenous microbiomes in both agricultural and environmental sectors. In agriculture, microbiomes from Himalayan regions have been suggested as better biofertilizers and biopesticides for the crops growing at low temperature and mountainous areas as they help in the alleviation of cold stress and other biotic stresses. Along with alleviation of low temperature, Himalayan microbes also have the capability to enhance plant growth by availing the soluble form of nutrients like nitrogen, phosphorus , potassium, zinc, and iron. These microbes have been recognized for producing plant growth regulators (abscisic acid, auxin, cytokinin, ethylene, and gibberellins). In the environment too, these microbes have been reported for bioremediating the environmental pollutants (pesticides, heavy metals, and xenobiotics). In this perspective, this review provides a detailed discussion on the ecology, biodiversity, and adaptive features of the native Himalayan microbiomes in view to achieve agro-environmental sustainability.
... The role of bacteria that solubilizes phosphate in promoting plant growth and the detoxification of PTMs is significant. Similarly, the use of mineralization and solubilization properties of PSB is an eco-friendly and economical method that provides a substantial amount of solubilized P to plants and improves the plant's growth (Selvakumar et al., 2008). ...
Phosphate-assisted phytoremediation has become an effective, economic, and environmentally sustainable process for the clean-up of potentially toxic metal(loid)s (PTMs)-contaminated soils. However, phosphate-induced phytoremediation efficiency can be enhanced depending upon PTMs concentration, plant species, and soil conditions. Phosphate-induced phytoremediation efficiency depends on several factors and phosphate interaction with soil components. Present chapter highlights that phosphate application has dual effects on the phytoremediation process, which may mobilize and or immobilize PTMs in soil. Besides, phosphate addition reduces PTMs toxicity and improve plants health. The role of microorganisms in regulating phosphate desolation and availability was also discussed. Depending on phosphate interaction with soil exchange sites, organic and inorganic components, nutrients, and microbial communities, it may have some advantages and disadvantages in phosphate-assisted phytoremediation of PTMs in soils. This chapter provides a comprehensive review of phosphate-assisted phytoremediation of PTMs in soil that can be an imperative resource for the scientific community working in multidisciplinary fields dealing with phytoremediation and PTMs contamination management.
... Siderophores production by P-solubilizing bacteria is a potent mechanism to ameliorate plant growth in iron limiting condition (Wani et al. 2007b;Ahmad et al. 2008). Several studies have revealed the excretion of siderophores from P-solubilizing microbes (Caballero-Mellado et al. 2007;Hamdali et al. 2008;Ahmad et al. 2008;Singh et al. 2008;Selvakumar et al. 2008;Jiang et al. 2008). As studies revealed that the mineral dissolution is dominant over ligand exchange via organic acid anions as a phosphate solubilizing process, it is obvious to consider the function of production of siderophores in increasing P-solubilization (Parker et al. 2005). ...
Endophytic bacteria survive in close association with their host plants. These bacteria become an integral part of the host tissue system. Almost every plant species is found to be in association with these bacteria. These are the promising agents that promote their host growth even in stressed environments, like in phytoremediation. They flourish their host’s growth either directly or indirectly. Directly by accumulating nutrients and modulating the level of phytohormones. Indirectly, by producing antibiotics, cell wall degrading enzymes, nutrient limitations, and activating resistance system of the host plant against the broad spectrum phytopathogens. Today these endophytic bacteria grab the attention of scientists, as these are the potential source of sustainable agriculture. Instead of using agrochemicals which are the main cause of soil health and environmental depletion, farmers should start using these endophytes as biocontrol agents, biofertilizers, biofungicides, in seed treatment, and in the reclamation of soil contaminated with heavy metals (phytoremediation). This application promotes sustainable agriculture and prevents the growing population of the world from future hazards in agriculture. Agriculture is the basic need for human survival so it requires the attention to be secured. In this chapter, we will go to the depth of the above-mentioned topics and more about the endophytes.
In the current age of fast-changing climate, food security is increasingly challenged. Modern agriculture has to boost the crop productivity in order to meet the needs of a continuously growing world population while adopting sustainable production systems to protect the environment and the human health. Climate-Smart agriculture (CSA) is an integrated approach combining several sustainable farming methods to mitigate adverse climate patterns. Current management strategies by prospecting plant–microbiome interactions in biotic and abiotic stress alleviation have been adopted in CSA. Although plant microbiomes have been extensively used as biofertilizers/biostimulants and biopesticides to enhance crop productivity and ameliorate plant health in the climate change context, research trends in plant–microbiome biotechnology are pointing out some shortcomings to be considered. More intensive research is still needed for better knowledge of the interactions prevailing within the trio plant–microbiome–environment to enhance the efficiency of microbial uses in CSA.
Bacterial species often comprise well-separated lineages, likely emerged and maintained by genetic isolation and/or ecological divergence. How these two evolutionary actors interact in the shaping of bacterial population structure is currently not fully understood. In this study, we investigate the genetic and ecological drivers underlying the evolution of Serratia marcescens, an opportunistic pathogen with high genomic flexibility and able to colonise diverse environments. Comparative genomic analyses reveal a population structure composed of five deeply-demarcated genetic clusters with open pan-genome but limited inter-cluster gene flow, partially explained by Restriction-Modification (R-M) systems incompatibility. Furthermore, a large-scale research on hundred-thousands metagenomic datasets reveals only a partial habitat separation of the clusters. Globally, two clusters only show a separate gene composition coherent with ecological adaptations. These results suggest that genetic isolation has preceded ecological adaptations in the shaping of the species diversity, an evolutionary scenario coherent with the Evolutionary Extended Synthesis.
Cold stress is one of the main obstacles to developing high-quality crops and global food security. Numerous molecular, physiological, and biochemical modifications occur in plants under different cold environments. Therefore, providing eco-friendly, economically viable, and sustainable solutions for guaranteeing high-quality food production in cold regions becomes essential. Crop growth and development in low-temperature environments may be improved using cold-tolerant microorganisms (CTMs). CTMs offer an eco-friendly and cost-effective way to shield crops from damage caused by cold stress. They can also stimulate crop development by regulating the production of phytohormones, increasing nutrient uptake, controlling siderophores, and activating the antioxidant system in cold environments. As a result, it is crucial to explore the interactions of plants with CTMs in cold climates, which may serve as a critical cold-stress engineer to address high-altitude farming difficulties worldwide. In this chapter, we explore the role and mechanisms used by CTMs to increase agricultural output sustainably in cold environments, highlighting the challenges facing their application.
This book sheds light on exciting advancements in plant protection technology that have the potential to revolutionise the way we safeguard our crops. It explores a range of topics, including pest management strategies, artificial intelligence, and biotechnological applications, to name a few. This book is a repository hub of knowledge.
Microbial compost plays a crucial role in improving soil health, soil fertility, and plant biomass. These biofertilizers, based on microorganisms, offer numerous benefits such as enhanced nutrient acquisition (N, P, and K), production of hydrogen cyanide (HCN), and control of pathogens through induced systematic resistance. Additionally, they promote the production of phytohormones, siderophore, vitamins, protective enzymes, and antibiotics, further contributing to soil sustainability and optimal agricultural productivity. The escalating generation of organic waste from farm operations poses significant threats to the environment and soil fertility. Simultaneously, the excessive utilization of chemical fertilizers to achieve high crop yields results in detrimental impacts on soil structure and fertility. To address these challenges, a sustainable agriculture system that ensures enhanced soil fertility and minimal ecological impact is imperative. Microbial composts, developed by incorporating characterized plant-growth-promoting bacteria or fungal strains into compost derived from agricultural waste, offer a promising solution. These biofertilizers, with selected microbial strains capable of thriving in compost, offer an eco-friendly, cost-effective, and sustainable alternative for agricultural practices. In this review article, we explore the potential of microbial composts as a viable strategy for improving plant growth and environmental safety. By harnessing the benefits of microorganisms in compost, we can pave the way for sustainable agriculture and foster a healthier relationship between soil, plants, and the environment.
Amongst the various abiotic stresses, cold is an essential factor that limits crop productivity worldwide. Low temperature affects the growth, development, and distribution of agronomic species around the world. To improve the understanding of the physiological and genetic properties and functions affecting potato cold tolerance, in this study, transcriptomic analysis was performed on two potato cultivars (HZ88 and LS6) with different cold tolerances that were treated at low temperature for 0, 1, 3, and 6 h. Transcriptomic analysis showed large differences between HZ88 and LS6 regarding the expression levels of low-temperature responsive genes. Notably, HZ88 responds to low-temperature stress via genes primarily enriched in plant hormone signal transduction, cutin, suberine, and wax biosynthesis, and photosynthesis-antenna proteins. By comparison, the most significant low-temperature responsive genes of LS6 were determined to be enriched in plant-pathogen interactions, zeatin biosynthesis, and plant hormone signal transduction. The cuticle, a horny waxy layer, is an important protective barrier formed by plants to resist biotic and abiotic stresses during the long-term ecological adaptation. This may be a physical defence employed by HZ88 to strengthen its cold resistance. In the LS6 cultivar, potatoes tend to cope with cold stress by strengthening their immune system and regulating hormone signal transduction. In addition, hormone pathway-related genes such as ABA, ICE-CBF signalling pathway-related genes, and genes encoding transcription factors all exhibited different expression patterns between HZ88 and LS6. To the best of our knowledge, this study is the first to elucidate the genetic mechanisms underlying the differences in cold resistance between the cold-tolerant LS6 and cold-sensitive HZ88, thereby establishing the foundation for further analysis and genetic breeding of potatoes.
Low temperatures greatly affect plant growth. In addition to the development of its own protection mechanisms, plants may rely on microorganisms to help them cope with cold. Because Valerianella locusta (lamb's lettuce) is a cold-adapted plant, it represents an interesting plant to understand how cold affects the root bacteriome. By means of amplicon sequencing of 16S ribosomal RNA genes, we identified the taxa forming the main cold root bacteriome of lamb's lettuce. The analysis of the root microbiome of a naturally growing V. locusta population and the study of the changes in the root microbiome of cultivated V. locusta grown under cold and ambient conditions allowed us to detect four cold-responsive families, of which Oxalobacteraceae presented the strongest shift under chilling temperatures. Moreover, the plant genotype had a small but significant effect on the response of the root bacteriome to cold. Finally, several bacterial candidates were discovered that may possibly alleviate the effect of low temperatures on plant fitness; namely, Massilia ASV2, Flavobacterium ASV5 and ASV11, or Acidovorax ASV20. However, currently, only 10 cold-enriched isolates could be obtained in cultivation, of which Flavobacterium R-83141; Polaromonas R-83176, R-83177, and R-83175; and Acidovorax R-83129 were able to increase either the root, shoot, or total fresh weight of a cold-sensitive ecotype of Arabidopsis thaliana (Cvi-0). Our results provide an overview of the taxa forming the root microbiome of this species and of the compositional shift that occurs under cold temperature treatment, demonstrating the impact of low temperatures on the composition of the root microbiome.
[Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .
Abiotic stresses such as drought, salinity, temperature, flooding and heavy metal toxicity reduce crop yield. About 64% of land worldwide is affected by drought. The lack of moisture in crops may lead to 50% yield loss, and increases soil salinity levels. Therefore, the use of plant growth promoting rhizobacteria for increasing plant stress tolerance appears as a sustainable strategy. Here we review abiotic stress tolerance mediated by plant growth promoting rhizobacteria in plants with focus on phytohormones, improved physiological attributes, root system architecture and regulation of the osmotic balance. Improved antioxidant activity result in reduced oxidative damage, which promotes plant growth, and nutrient and water uptake. Other extracellular secretions trap ions and moisture and improve the growth environment. Emissions and elicitors function as signaling molecules that induce genes and transcription factors belonging to the stress responsive pathways. The use of plant growth-promoting rhizobacterial bioinoculants is effective in enhancing tolerance to crop abiotic stress. The formulations and application of these microorganisms is promising for climate smart agriculture.
Main Conclusion
The responses of plants to different abiotic stresses and mechanisms involved in their mitigation are discussed. Production of osmoprotectants, antioxidants, enzymes and other metabolites by beneficial microorganisms and their bioengineering ameliorates environmental stresses to improve food production.
Abstract
Progressive intensification of global agriculture, injudicious use of agrochemicals and change in climate conditions have deteriorated soil health, diminished the microbial biodiversity and resulted in environment pollution along with increase in biotic and abiotic stresses. Extreme weather conditions and erratic rains have further imposed additional stress for the growth and development of plants. Dominant abiotic stresses comprise drought, temperature, increased salinity, acidity, metal toxicity and nutrient starvation in soil, which severely limit crop production. For promoting sustainable crop production in environmentally challenging environments, use of beneficial microbes has emerged as a safer and sustainable means for mitigation of abiotic stresses resulting in improved crop productivity. These stress-tolerant microorganisms play an effective role against abiotic stresses by enhancing the antioxidant potential, improving nutrient acquisition, regulating the production of plant hormones, ACC deaminase, siderophore and exopolysaccharides and accumulating osmoprotectants and, thus, stimulating plant biomass and crop yield. In addition, bioengineering of beneficial microorganisms provides an innovative approach to enhance stress tolerance in plants. The use of genetically engineered stress-tolerant microbes as inoculants of crop plants may facilitate their use for enhanced nutrient cycling along with amelioration of abiotic stresses to improve food production for the ever-increasing population. In this chapter, an overview is provided about the current understanding of plant–bacterial interactions that help in alleviating abiotic stress in different crop systems in the face of climate change. This review largely focuses on the importance and need of sustainable and environmentally friendly approaches using beneficial microbes for ameliorating the environmental stresses in our agricultural systems.
The interaction of silicon and soil microorganisms stimulates crop enhancement to ensure sustainable agriculture. Silicon may potentially increase nutrient availability in rhizosphere with improved plants’ growth, development as it does not produce phytotoxicity. The rhizospheric microbiome accommodates a variety of microbial species that live in a small area of soil directly associated with the hidden half plants’ system. Plant growth-promoting rhizobacteria (PGPR) play a major role in plant development in response to adverse climatic conditions. PGPRs may enhance the growth, quality, productivity in variety of crops, and mitigate abiotic stresses by reprogramming stress-induced physiological variations in plants via different mechanisms, such as synthesis of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate deaminase, exopolysaccharides, volatile organic compounds, atmospheric nitrogen fixation, and phosphate solubilization. Our article eye upon interactions of silicon and plant microbes which seems to be an opportunity for sustainable agriculture for series of crops and cropping systems in years to come, essential to safeguard the food security for masses.
Seeds are a vector of genetic progress and, as such, they play a significant role in the sustainability of the agri-food system. The current global seed market is worth USD 60 billion that is expected to reach USD 80 billion by 2025. Seeds are most often treated before their planting with both chemical and biological agents/products to secure good seed quality and high yield by reducing or preventing losses caused by diseases. There is increasing interest in biological seed treatments as alternatives to chemical seed treatments as the latter have several negative human health and environmental impacts. However, no study has yet quantified the effectiveness of biological seed treatments to enhance crop performance and yield. Our meta-analysis encompassing 396 studies worldwide reveals for the first time that biological seed treatments significantly improve seed germination (7±6%), seedling emergence (91±5%), plant biomass (53±5%), disease control (55±1%), and crop yield (21±2%) compared to untreated seeds across contrasted crop groups, target pathogens, climatic regions, and experimental conditions. We conclude that biological seed treatments may represent a sustainable solution to feed the increasing global populations while avoiding negative effects on human health and ensuring environmental sustainability.
The concept of soil health refers to specific soil properties and the ability to support and sustain crop growth and productivity, while maintaining long-term environmental quality. The key components of healthy soil are high populations of organisms that promote plant growth, such as the plant growth promoting rhizobacteria (PGPR). PGPR plays multiple beneficial and ecological roles in the rhizosphere soil. Among the roles of PGPR in agroecosystems are the nutrient cycling and uptake, inhibition of potential phytopathogens growth, stimulation of plant innate immunity, and direct enhancement of plant growth by producing phytohormones or other metabolites. Other important roles of PGPR are their environmental cleanup capacities (soil bioremediation). In this work, we review recent literature concerning the diverse mechanisms of PGPR in maintaining healthy conditions of agricultural soils, thus reducing (or eliminating) the toxic agrochemicals dependence. In conclusion, this review provides comprehensive knowledge on the current PGPR basic mechanisms and applications as biocontrol agents, plant growth stimulators and soil rhizoremediators, with the final goal of having more agroecological practices for sustainable agriculture.
As a natural engineer, Plant Growth Promoting Rhizobacteria (PGPR) play an important role in increasing plant growth, yield and enhancing plant tolerance to stressful conditions. These beneficial bacteria take up their position in the rhizosphere, around the plants’ root tissues. They may be in, or on their host tissues and help to provide nutrients to their host plants. For sustainable agriculture, PGPR transmit their extensive assistance in ecosystem management, soil structure maintenance, stress management and plant morphology and physiology modulation in an environmentally friendly manner. Plant- PGPR interactions also stimulate nutrient acquisition and accumulation, improve plant performance and enhance plants’ tolerance to abiotic and biotic stresses. Beside these, PGPR are good biofertilizers and safe for our environment. Nanotechnological advances with PGPR applications are important today to increase the impact of PGPR in agriculture. Undoubtedly, PGPR concept is intimately involved with agriculture, horticulture, forestry and they are too enough to establish a vibrant environment. In this review we have focused on the versatility of PGPR-their performance and aimed to address some future prospects of PGPR as an eco-friendly tool for plant growth regulation.
For complete growth and development of plants phosphorous (P) is the second key nutrient after nitrogen. Predominantly two major forms of phosphorous exist in soil: organic P and inorganic P, which are however mostly in insoluble forms. This unavailability of P is the result of fixation and precipitation, which causes P inadequacy and limits the growth of plants. To reassure the nutritional demand of crop, P is generally incorporated in soil in the form of chemical P fertilizer. However, the use of mineral P fertilizer has very long-term implications in the environment such as eutrophication, soil fertility depletion, and aggregation of harmful chemicals. So, it is important to generate alternative sustainable and economical method to fulfil the P requirements. In this regard, phosphate solubilizing microbes including P-solubilizing bacterial endophytes provided an unconventional and eco-friendly biotechnological solution to accomplish the phosphorous demands of crops. The bacterial endophytes are used as bio-inoculants and facilitate the growth of plants in many ways other than P- solubilization. This work emphasized on the plant colonizing ability of endophytic bacteria, their functional diversity and process involved in phosphorous solubilization or mineralization mechanism for their possible use to attain sustainable agriculture system.KeywordsSoil PBacterial endophytesP-solubilization/mineralizationBio-inoculantsSustainable agriculture
Abiotic stresses are major constraints for worldwide agricultural productivity. Several adaptations and mitigations are required by plants to combat abiotic stresses. Plant develops physiological, biochemical, and morphological responses to overcome the adverse effects of these stresses. Higher forms of flora and fauna maintain crucial interactions with microorganisms. The theme of this chapter prioritizes endophytic bacteria and their underlying mechanisms, which help in increasing plant stress tolerance through various direct and indirect processes. We highlight the functional aspects of endophytic bacterial species to withstand unfavourable effects of abiotic stressors.KeywordsBiotic stressAbiotic stressBioremediationPlant growth and promotionPlant health
Plant rhizosphere has been a preferred ecological niche for different types of microorganisms due to the rich nutrient availability. Bacteria residing in the rhizosphere, termed as rhizobacteria, have received a great attention for their possible utilization as biofertilizers and biocontrol agents for improving soil health and enhancing the plant growth in a sustainable manner. These rhizobacteria positively affect the plant growth and yield by various direct and indirect mechanisms. They carry out the processes of nitrogen fixation and solubilization of phosphates, zinc, manganese, and iron, lowering of ethylene levels by producing 1-aminocyclopropane-1-carboxylate and the production of phytohormones, siderophores, ammonia, and various enzymes. However, the effectiveness of rhizobacteria is limited by variability and inconsistency in their field performance due to stress imposed by various environmental factors and competition with the native microorganisms. The selection of stress-tolerant and rhizosphere-competent rhizobacteria with multiple plant growth-promoting traits is important for their successful utilization as microbial inoculants.
Crop plants are more often exposed to abiotic stresses in the current age of fast-evolving climate change. This includes exposure to extreme and unpredictable changes in climatic conditions, phytosanitary hazards, and cultivation conditions, which results in drastic losses in worldwide agricultural productions. Plants coexist with microbial symbionts, some of which play key roles in the ecosystem and plant processes. The application of microbial biostimulants, which take advantage of symbiotic relationships, is a long-term strategy for improving plant productivity and performance, even in the face of climate change-associated stresses. Beneficial filamentous fungi, yeasts, and bacteria are examples of microbial biostimulants, which can boost the growth, yield, nutrition and stress tolerance in plants. This paper highlights recent information about the role of microbial biostimulants and their potential application in mitigating the abiotic stresses occurring on crop plants due to climate change. A critical evaluation for their efficient use under diverse climatic conditions is also made. Currently, accessible products generally improve cultural conditions, but their action mechanisms are mostly unknown, and their benefits are frequently inconsistent. Thus, further studies that could lead to the more precisely targeted products are discussed.
Entomopathogenic bacteria are commonly used as biological agents to control different insect pests. However, little is known about the role of bacterial entomopathogens as endophytes in regulating both plant growth and resistance against insect pests. Here, we applied the entomopathogenic bacterium Serratia marcescens S-JS1 via rice seed inoculation and evaluated its effects on host plant growth and resistance against the rice pest Nilaparvata lugens. Furthermore, the induction of defense-related secondary metabolites by the bacterium was assessed by GC–MS/MS. We showed that S-JS1 was able to endophytically colonize the roots and shoots of rice seedlings following seed inoculation. Colonized plants showed increased seed germination (9.4–13.3%), root (8.2–36.4%) and shoot lengths (4.1–22.3%), and root (26.7–69.3%) and shoot fresh weights (19.0–49.0%) compared to plants without inoculation. We also identified the production of indole-3-acetic acid by S-JS1, which is likely involved in enhancing rice plant growth. In a two-choice test, N. lugens adults preferred to feed on untreated control plants than on plants treated with S-JS1. In the no-choice feeding tests, the survival of N. lugens nymphs that fed on S-JS1-treated plants was significantly lower than that of nymphs that fed on untreated plants. Additionally, seeds treated with 10⁹ cfu/ml S-JS1 resulted in elevated levels of secondary metabolites, which may be associated with N. lugens resistance in rice plants. Therefore, we suggest that the entomopathogenic bacterium S. marcescens be considered a potentially promising endophyte for use in an innovative strategy for the integrated management of insect pests.
Microorganisms are ubiquitous and diverse microbes inhabit low-temperature niches. More than three quarters of the Earth’s surface is either occasionally cold or permanently frozen, making it a predominant habitat in the world. Despite such hostile conditions, these organisms flourish because of certain structural, physiological, and molecular variations that are associated with it. Adaptations related to the cell membrane, enzymes, transporters, chaperones, antifreeze proteins, osmolytes, and cold- and heat-shock proteins help the organisms in thriving under such situations. In the present chapter, we discussed various microbial adaptations in detail to throw light on the lifestyle microorganisms thriving under low temperature. Understanding such adaptations may assist us with investigating the prospects for advancement in various novel biotechnological applications.
Abiotic and biotic factors typically interact with each other and are the primary determinants of the agricultural yield especially for the cultivated crops growing at exotic locations. Abiotic factors naturally affect microflora of the soil therefore influencing the ecosystem responsible for the potential growth of cultivated plants. Cold-adapted microorganisms are capable of not merely enduring the harsh and adverse climatic conditions, but they are equally able to efficiently produce functionalities useful for the flourishing of plants at subzero temperatures. Several key factors are responsible for the tolerance and possible survival of the cold conditions by the specific microorganisms endowed with distinctive features like notable production of plant growth-promoting factors and typically inducing effective resistance for the plants to tolerate biotic as well as abiotic stresses. Apart from their potential use in sustainable agriculture in inhospitable conditions, microbes could be conveniently used to produce various enzymes suitable for its use in industries and pharmaceuticals. Some of the specific organisms typically possess the enhanced capability to staunchly resist and degrade hazardous pollutants with possible use in managing wastes and cleaning oil spills at low temperatures. Bioprospecting of beneficial microorganisms from unexplored niches could undoubtedly help to carefully develop formulations capable of inducing successful resistance in plants to abiotic stresses and biofertilization of arid soils inevitably leading to considerable advancement of intensive agriculture and increase productivity in arid regions with low nutrition and harsh climatic conditions along with the successful production of various functionalities suitable for its use in various industrial sectors.
The versatility displayed by kingdom Fungi in terms of physiological, genomic and metabolic complexities has ensured their presence in all major ecosystems. Given that 85% of the Earth experiences cold temperatures of below 5 °C, either seasonally or permanently, there is no shortage of cold environments resulting in global distribution of psychrophilic and psychrotrophic fungi. The cold-adapted extremophilic fungi possess molecular adaptations to persist and proliferate against harsh conditions exerted on them by their environment such as multiple freeze-thaw cycles, desiccation, low water activity, high exposure to harmful UV radiation or complete absence, high hydrostatic pressure and low nutrient availability. Cold habitats include polar regions such Antarctica and the Arctic as well as non-polar regions such as the deep seas and alpine regions. These regions offer a broad spectrum of niches for colonization of fungi including but not limited to rocks, ice sheets, snow cover, glaciers, cold soils, frozen seas, freshwater ice and permafrost, with varying levels of abundance and diversity.
A major part of earth experiences less than 5 °C temperature, adversely affecting agricultural productivity. Water, the most important factor for existence of living organisms nearly freezes at such temperatures and becomes unavailable for utilization. Frozen soils and chilled/ frozen water challenge the survivability of plants, thus reducing crop yields to a large extent. Some parts of the world experience subzero temperature, reduced kinetics, and scarcity of nutrient and water conditions, thereby challenging the survival of autochthonous biota too. But, even under icy conditions, soil microorganisms playing a vital role in agriculture, are well adapted due to evolution of diverse mechanisms to overcome and perform better, making them a potent source to be tapped for increasing productivity under cold stress. They employ various methods like altering cell envelope, energy metabolism and membrane fluidity, quenching reactive oxygen species, production of compatible solutes, cold shock proteins, and exopolysaccharides in alleviation of cold stress in plants. However, such bioinoculants in cold regions are yet to be fully mined for their capability.
Currently, plant diseases and insect infestations are mainly controlled by the extraneous application of pesticides. Unfortunately, the indiscriminate use of such agrochemicals can cause ecological and environmental problems, as well as human health hazards. To obviate the potential pollution arising from the application of agrochemicals, biological control of soilborne pathogens or insect pests using antagonistic microorganisms may be employed. Certain soil bacteria, algae, fungi, plants and insects possess the unique ability to produce hydrogen cyanide (HCN), which plays an important role in the biotic interactions of those organisms. In particular, cyanogenic bacteria have been found to inhibit the growth of various pathogenic fungi, weeds, insects, termites and nematodes. Thus, the use of HCN-producing bacteria as biopesticides offers an ecofriendly approach for sustainable agriculture. The enzyme, HCN synthase, involved in the synthesis of HCN, is encoded by the hcnABC gene cluster. The biosynthetic regulation of HCN, antibiotics and fluorescent insecticidal toxins through the conserved global regulatory GacS/GacA system is elaborated in this review, including approaches that may optimize cyanogenesis for enhanced pest control. In addition, the effects of bacterially synthesized HCN on the production of indole acetic acid, antibiotics and fluorescent insecticidal toxins, 1-aminocyclopropane-1-carboxylate deaminase utilization and phosphate solubilization may result in the stimulation of plant growth. A more detailed understanding of HCN biosynthesis and regulation may help to elaborate the precise role of this compound in biotic interactions and sustainable agriculture.
Mitigation of abiotic stress in crops is a feature attributed to various so-called biostimulants based on plant growth-promoting microorganisms (PGPMs) plant-, compost- and seaweed extracts, protein hydrolylates, chitosan derivatives etc. but also to mineral nutrients with protective functions, such as zinc (Zn), manganese (Mn), boron (B), calcium (Ca) and silicon (Si), recommended as stress protectants in commercial formulations. This study focussed on the effects of selected biostimulants on cold stress mitigation during early growth in maize, as a major stress factor for cultivation of tropical and subtropical crops in temperate climates. Chilling stress and micronutrient supplementation Chilling stress, induced by moderately low soil temperatures (8-14°C) in a controlled root cooling system, was associated with inhibition of shoot growth, oxidative leaf damage (chlorosis, necrosis accumulation of stress anthocyanins) and a massive decline in root length (Chapter 4 and 5). Due to inhibition of root growth, nutrient acquisition in general was impaired. However, nutrient deficiencies were recorded particularly for the micronutrients zinc (Zn) and manganese (Mn). The impaired Zn and Mn status was obviously related with the observed limitations in plant performance, which were reverted by exogenous Zn and Mn supplementation (0.5 mg plant-1), finally leading to restored nutrient acquisition and improved plant recovery after termination of the cold stress period. Zinc and manganese deficiency was mainly related with impaired uptake of the micronutrients, since the cold stress-induced deficiency symptoms persisted even in hydroponic culture when all nutrients were freely available. Beneficial effects of Zn/Mn supplementation were only detectable when the micronutrients were supplied prior to the onset of the stress period via seed soaking, seed dressing or fertigation, when uptake and internal translocation was still possible. A transcriptome analysis of the shoot tissue (Chapter 5) revealed 1400 differentially expressed transcripts (DETs) after 7-days exposure of maize seedlings to chilling stress of 12°C, mostly associated with down-regulation of selected functional categories (BINs), related with photosynthesis, synthesis of amino acids, lipids and cell wall precursors, transport of mineral nutrients (N, P, K,), metal handling and synthesis of growth hormones (auxins, gibberellic acid) but also of jasmonic (JA) and salicylic acids (SA) involved in stress adaptations. In accordance with the impaired micronutrient status and oxidative leaf damage in response to the cold stress treatments, downregulation was also recorded for transcripts related with oxidative stress defence (superoxide dismutases SOD, catalase, peroxidases POD, synthesis of phenylpropanoids and lignification), particularly dependent on the supply of micronutrients as co-factors. Upregulation was recorded for BINs related with degradation of lipids, of cell wall precursors, synthesis of waxes and certain flavonoids and of stress hormones, such as abscisic acid (ABA) and ethylene but degradation of growth-promoting cytokinins (CK). Accordingly, supplementation of Zn and Mn increased the accumulation of anthocyanins and antioxidants, the activities of superoxide dismutase and peroxidases, associated with reduced ROS accumulation (H2O2), mitigation of oxidative leaf damage and improved plant recovery at the end of the cold stress period (Chapter 5 and 6). Effects of seaweed extracts Cold-protective properties similar to Zn/Mn supplementation, associated with an improved Zn/Mn-nutritional status and reduced oxidative damage, were recorded also after fertigation with seaweed extracts prior to the onset of the stress treatments (Chapter 4). However, this effect was detectable only with seaweed extract formulations rich in Zn/Mn (Algavyt+Zn/Mn; Algafect; 6-70 mg kg DM-1) but not with a more highly purified formulation (Superfifty) without detectable micronutrient contents. This finding suggests that the cold-protective effect by soil application of seaweed extracts is based on an improved micronutrient supply and not to an elicitor effect, frequently reported in the literature for stress-protective functions after foliar application of seaweed extracts. Silicon fertilization Similar to seaweed extracts, also silicon (Si), applied by seed soaking or fertigation with silicic acid, mimicked the cold-protective effects of Zn/Mn supplementation in maize seedlings (Chapter 5). The Zn/Mn status of the Si-treated plants was improved although, in this case no additional micronutrient supply was involved. However, Si application significantly reduced leaching losses of Zn/and Mn by 50-70%, as a consequence of cold stress-induced membrane damage in germinating maize seeds and favoured the root to shoot translocation of Zn. This was associated with a restoration of gene expression, similar to the profiles recorded for unstressed control plants. However, the expression of genes related with synthesis and signal transduction of ABA, as central regulator of adaptive cold stress responses in plants, was even more strongly upregulated than in the cold-stressed controls. Accordingly, expression of cold stress adaptations involved in oxidative stress defence (SOD, peroxidases, phenolics, antioxidants) and the reduction of oxidative leaf damage and improved plant recovery were similar to the plants with Zn/Mn supplementation. Plant growth promoting microorganisms Cold-protective functions were recorded also for selected microbial inoculants (Chapter 6). However, out of five tested inoculant formulations, based on strains of Pseudomonas sp., DSMZ13134, Bacillus amyloliquefaciens FZB42, Bacillus atrophaeus ABI05, Penicillium sp. PK112 (BFOD) and a consortium of Trichoderma harzianum OMG16 and five Bacillus strains (Combi-A), a significant protective effect was detectable only for Penicillium sp. and particularly for CombiA. The CombiA consortium significantly increased root length and reduced oxidative leaf damage of cold-stressed plants, associated with increased SOD and POD activities and accumulation of phenolics and antioxidants. Root growth stimulation was related with increased IAA (indole acetic acid) tissue contents and increased expression of genes involved in IAA biosynthesis (ZmTSA) transport (ZmPIN1A) and perception (ZmAFR12). The tissue concentrations of ABA were not affected by the microbial inoculants, but the shoot concentrations of JA and SA increased, suggesting an effect by induced systemic resistance (ISR). Moreover, root concentrations of cytokinins (CKs) as ABA antagonists and expression of IPT genes involved in CK biosynthesis declined, leading to an increased ABA/cytokinin ratio and accordingly to increased expression of ABA responsive genes (ZmABF2). These findings suggest that CombiA mainly acted via improvement of root growth and nutrient acquisition by activation of the plant auxin metabolism and activation of cold protective metabolic responses by induction of ISR via JA/SA signalling and ABA-mediated responses, due to inhibition of CK biosynthesis. Synergistic interactions While the different cold-stress protectants investigated in this study induced similar protective plant responses, synergistic effects were obtained by combined applications (Chapter 6). The combination of CombiA inoculation with Zn/Mn supplementation further increased the plant micronutrient status and the cold-protective effects of CombiA. For all treatments, generally the expression of cold-protective effects was further improved by use of DMPP-stabilized ammonium fertilizers instead of nitrate fertilization. Ammonium fertilization promoted micronutrient acquisition via root-induced rhizosphere acidification, increased the ABA shoot concentrations with a moderate activation of metabolic cold stress responses and stimulated root colonization of Trichoderma harzianum OMG16 (CombiA). Field performance A comparative evaluation of the various cold protectants under field conditions with stabilized ammonium starter fertilization, revealed a severely reduced seedling emergence at six weeks after sowing (44%) due to extremely cold and wet soil conditions by the end of April in 2016, associated with a low Zn-nutritional status (32 mg kg-1 shoot DM). Significant improvements were recorded particularly for starter treatments including Zn/Mn seed dressing (emergence 56%) or seed priming with K2SiO4 (emergence 72%) and also by inoculation with the fungal PGPM strain Penicillium sp. BFOD (emergence 49%) associated with a doubling of the Zn tissue concentrations. Even after re-sowing, a significant yield increase for silo maize was recorded exclusively for the K2SiO4 treatment (Chapter 5). Taken together, the findings suggest that exploitation of synergistic interactions by combined starter applications of protective nutrients with selected biostimulants, could offer a cost-effective option for cold-stress prophylaxis in sensitive crops.
Extreme events of abiotic stress conditions such as high temperatures, prolonged drought, salinity, metal toxicity, intense rains, flooding, frost, and low temperatures affect the productivity of crops as well as significantly affect plants and soil microorganisms. The composite and active connections between microorganisms and plant roots during abiotic stress disturb not only the plants but also the physical, chemical, and structural properties of soil. While several studies have found that numerous species of microorganisms, particularly rhizospheric microorganisms generate diverse mechanisms to enhance both plants and their survival ability against abiotic stresses. Among the microorganisms, plant growth-promoting rhizobacteria (PGPR) and Arbuscular mycorrhiza fungi (AMF) were found to be the most important species that enhance plant to mitigate the adverse events of abiotic stress through the production of exopolysaccharides, cytokinins, antioxidants, and enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase and also the formation of biofilm. Besides theses production of organic compounds, dual symbiotic systems of PGPR and AMF (endophytic rhizospheric bacteria and symbiotic fungi) also stimulate to alleviate the adverse effect of abiotic stress in plants. The current book chapter discusses the role of soil microorganisms in plant adaptation to abiotic stresses and also highlights the current scenario, future perspectives, and challenges to use for the sustainability of crop production under the future extreme events of climate change.
This book is published in the hopes of sharing the new research and findings in the
field of life science subjects. Life science can help us unlock the mysteries of our universe,
but beyond that, conquering it can be personally satisfying. We developed this digital book
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Exponential upsurge in the global population growth rate claims sustainable means to fulfill their food requirements. Therefore, the collaboration of beneficial microorganisms with their host plants have been of interest for years as these associations can be helpful in the development of sustainable agriculture. However, the endophytic microorganisms develop a strong and persistent interaction with the host plants compared to epiphytic microbes. The origin of plant-associated endophytes was supposed to be from seeds as the endophytic microbes were found inside seeds of several plant species although, endophytes do not necessarily come from seeds only but can also enter the roots or other parts during plant growth. In any case, the richness of seed with the microbes and their dynamics can edify innovative research potentials in the field of plant-microbe associations. Yet, the seed microbiome is often underrepresented in plant microbial studies and is least studied up till now compared to phyllospheric or rhizospheric microbial population. The revival of exploring the seed micro-biome is stimulating new insights related to the dynamics and diversity of seed microbiome along with their interconnectedness with the soil and plant microbial community as well as the microbes associated with polli-nators and dispersers. This review is an effort to acknowledge the research on seed associated microbial community including bacteria and fungi. It focuses on ecology of seed microbiome from sources to diversity, their association with the host plant, and their life cycle including mode of colonization, localization, and transmission. Both the horizontal and vertical means of transmission have been discussed in this paper whereas the significance of vertical transmission for rapid infection of beneficial microbial community to next generations of plants through seeds is emphasized. Moreover, the applications of seed endophytes for growth promotion of plants, as biocontrol agents and in phytoremediation are discussed. Finally, the association of seed endophytes with seed quality is linked.
Low-temperatures pose extreme challenges to crops causing significant economical impacts. Frosts are responsible for more than 30% of weather-related insured crop losses in some temperate climate jurisdictions, but are particularly devastating for small holdings and communities reliant on a bountiful harvest. Low-temperatures are also frequently accompanied by other abiotic and biotic stresses, including pathogen attacks. Some pathogens have sub-zero temperature optima, while others leverage low-temperatures to promote freezing at high sub-zero temperatures by way of ice-nucleating proteins in order to access intracellular nutrients. To survive low-temperatures and the attendant risks, various plant species have evolved complex and intricate signaling networks, molecular mechanisms, and physiological changes, in addition to symbiotic relationships with microbiota. Enhancing low-temperature survival and pathogen-induced freezing tolerance in cold susceptible, agriculturally significant crops is an attractive area of research with immense translatable value to all aspects of society. This area of research will be particularly important in our near future as climate change increases the unpredictability of frosts, particularly in the spring and autumn. Against this backdrop, the world population continues to grow while arable land remains finite and wealth inequality exacerbates food poverty. In this review, we examine plant i) low-temperature stress, ii) cold acclimation responses, particularly in crops iii) antifreeze proteins, and iv) frost-associated pathogens. Lastly, we suggest integrated approaches to improve crop frost tolerance.
With its theoretical basis firmly established in molecular evolutionary and population genetics, the comparative DNA and protein sequence analysis plays a central role in reconstructing the evolutionary histories of species and multigene families, estimating rates of molecular evolution, and inferring the nature and extent of selective forces shaping the evolution of genes and genomes. The scope of these investigations has now expanded greatly owing to the development of high-throughput sequencing techniques and novel statistical and computational methods. These methods require easy-to-use computer programs. One such effort has been to produce Molecular Evolutionary Genetics Analysis (MEGA) software, with its focus on facilitating the exploration and analysis of the DNA and protein sequence variation from an evolutionary perspective. Currently in its third major release, MEGA3 contains facilities for automatic and manual sequence alignment, web-based mining of databases, inference of the phylogenetic trees, estimation of evolutionary distances and testing evolutionary hypotheses. This paper provides an overview of the statistical methods, computational tools, and visual exploration modules for data input and the results obtainable in MEGA.
Phytophthora parasitica causes serious widespread, and difficult-to-control root rots in warmer regions. This oomycete is one of the most important pathogen of citrus. This paper reports the biological control of the pathogen by a strain of Serratia marcescens R-35, isolated from citrus rhizosphere. In greenhouse trials, the bacterium suppressed more than 50% of the disease and promoted the plant growth.Phytophthora parasitica é um oomiceto que causa sérios problemas fitossanitários em diferentes espécies de plantas em regiões tropicais e o controle tem sido difícil. Este patógeno é um dos mais importante à citricultura. Este trabalho relata o controle biológico do patógeno por uma linhagem de Serratia marcescens R-35, isolada da rizosfera de citros. Em condições de casa-de-vegetação, a bactéria reduziu em mais de 50% a incidência da doença, ao mesmo tempo que promoveu o crescimento de plantas.
The bacterial flora of the Oberea linearis (Coleoptera: Cerambycidae) was investigated and 13 different bacteria were isolated from O. linearis larvae. Seven of these bacteria were performed and characterized at species level and the rest of them were characterized
at genus level. In this study, we determined morphological and physiological characteristics of the bacterial isolates by
conventional and routine techniques, biochemical properties and metabolic enzyme profiles by API20E and Phoenix 1000A panel
test systems. Additionally, 16S rRNA gene sequence analysis was also performed to identify the isolates at the molecular level.
The isolates were identified as Acinetobacter calcoaceticus (Ol1), Enterobacter aerogenes (Ol2), Pseudomonas sp. (Ol3), Flavobacterium sp. (Ol4), Microbacterium sp. (Ol5), Enterobacter agglomerans (Ol6), Xanthomonas sp. (Ol7), Pseudomonas syringae (Ol8), Pseudomonas sp. (Ol9), Xanthomonas sp. (Ol10), Enterobacter cancerogenus (Ol11), Xanthomonas maltophilia (Ol12), and Serratia marcescens (Ol13). This is the first record of bacterial isolates (Ol5, Ol8, Ol11, Ol12) from any insect. All these bacteria were tested
against O. linearis larvae, and Serratia marcescens was found to cause the highest mortality (65%). On the other hand, we determined 90% mortality against this pest within four
days by utilizing spore and crystal mixture of Bacillus thuringiensis isolated from Melolontha melolontha.
The Ribosomal Database Project (RDP-II) provides the research community with aligned and annotated rRNA gene sequences, along
with analysis services and a phylogenetically consistent taxonomic framework for these data. Updated monthly, these services
are made available through the RDP-II website (http://rdp.cme.msu.edu/). RDP-II release 9.21 (August 2004) contains 101 632 bacterial small subunit rRNA gene sequences in aligned and annotated
format. High-throughput tools for initial taxonomic placement, identification of related sequences, probe and primer testing,
data navigation and subalignment download are provided. The RDP-II email address for questions or comments is rdpstaff{at}msu.edu.
Cucurbit yellow vine disease (CYVD), which can inflict heavy losses to watermelon, pumpkin, cantaloupe, and squash in U.S. production areas from the midwest to northeastern states, causes phloem discoloration, foliar yellowing, wilting, and plant decline. Bacteria were cultured from the phloem of crown sections of symptomatic plants of Citrullus lanatas and Cucurbita pepo. Those bacteria testing positive in CYVD-specific polymerase chain reaction (PCR) were all gram negative and appeared morphologically identical, producing creamy white, smooth, entire, convex colonies on Luria-Bertani or nutrient agar. Characterized cucurbit-derived strains of Serratia marcescens were introduced into greenhouse-grown squash plants by puncture inoculation and into field-grown squash plants by enclosure with S. marcescens-fed squash bugs, Anasa tristis. Up to 60% of the bacteria-inoculated plants in the greenhouse and up to 17% of field plants caged with inoculative squash bugs developed phloem discoloration and tested positive for S. marcescens by CYVD-specific PCR. None of the controls developed phloem discoloration or tested positive by PCR. Of the diseased field plants, 12% (2 of 35) also yellowed, wilted, and collapsed, exhibiting full symptom development of CYVD. However, neither plant collapse nor decline was observed in the greenhouse-grown, puncture-inoculated plants. The morphology, growth habit, and PCR reaction of bacteria cultured from crown tissue of a subset of plants in each experimental group were indistinguishable from those of the inoculum bacteria. Evidence presented from our studies confirms that the squash bug can transmit S. marcescens, the CYVD causal bacterium. The S. marcescens-A. tristis relationship described here is the first instance in which the squash bug has been identified as a vector of a plant pathogen. Our experiments represent a completion of the steps of Koch's postulates, demonstrating that S. marcescens is the causal agent of CYVD and that the squash bug, A. tristis, is a vector of the pathogen.
A universal method to detect and determine siderophores was developed by using their high affinity for iron(III). The ternary complex chrome azurol S/iron(III)/hexadecyltrimethylammonium bromide, with an extinction coefficient of approximately 100,000 M-1 cm-1 at 630 nm, serves as an indicator. When a strong chelator removes the iron from the dye, its color turns from blue to orange. Because of the high sensitivity, determination of siderophores in solution and their characterization by paper electrophoresis chromatography can be performed directly on supernatants of culture fluids. The method is also applicable to agar plates. Orange halos around the colonies on blue agar are indicative of siderophore excretion. It was demonstrated with Escherichia coli strains that biosynthetic, transport, and regulatory mutations in the enterobactin system are clearly distinguishable. The method was successfully used to screen mutants in the iron uptake system of two Rhizobium meliloti strains, DM5 and 1021.
CLUSTAL X is a new windows interface for the widely-used progressive multiple sequence alignment program CLUSTAL W. The new
system is easy to use, providing an integrated system for performing multiple sequence and profile alignments and analysing
the results. CLUSTAL X displays the sequence alignment in a window on the screen. A versatile sequence colouring scheme allows
the user to highlight conserved features in the alignment. Pull-down menus provide all the options required for traditional
multiple sequence and profile alignment. New features include: the ability to cut-and-paste sequences to change the order
of the alignment, selection of a subset of the sequences to be realigned, and selection of a sub-range of the alignment to
be realigned and inserted back into the original alignment. Alignment quality analysis can be performed and low-scoring segments
or exceptional residues can be highlighted. Quality analysis and realignment of selected residue ranges provide the user with
a powerful tool to improve and refine difficult alignments and to trap errors in input sequences. CLUSTAL X has been compiled
on SUN Solaris, IRIX5.3 on Silicon Graphics, Digital UNIX on DECstations, Microsoft Windows (32 bit) for PCs, Linux ELF for
x86 PCs, and Macintosh PowerMac.
Six closely related N2-fixing bacterial strains were isolated from surface-sterilized roots and stems of four different rice varieties. The strains
were identified as Serratia marcescens by 16S rRNA gene analysis. One strain, IRBG500, chosen for further analysis showed acetylene reduction activity (ARA) only
when inoculated into media containing low levels of fixed nitrogen (yeast extract). Diazotrophy of IRBG500 was confirmed by
measurement of15N2 incorporation and by sequence analysis of the PCR-amplified fragment of nifH. To examine its interaction with rice, strain IRBG500 was marked with gusAfused to a constitutive promoter, and the marked strain was inoculated onto rice seedlings under axenic conditions. At 3 days
after inoculation, the roots showed blue staining, which was most intense at the points of lateral root emergence and at the
root tip. At 6 days, the blue precipitate also appeared in the leaves and stems. More detailed studies using light and transmission
electron microscopy combined with immunogold labeling confirmed that IRBG500 was endophytically established within roots,
stems, and leaves. Large numbers of bacteria were observed within intercellular spaces, senescing root cortical cells, aerenchyma,
and xylem vessels. They were not observed within intact host cells. Inoculation of IRBG500 resulted in a significant increase
in root length and root dry weight but not in total N content of rice variety IR72. The inoculated plants showed ARA, but
only when external carbon (e.g., malate, succinate, or sucrose) was added to the rooting medium.
Serratia marcescens isolated from raw milk was found to produce extracellular lipase. The growth of this organism could contribute to flavor defects in milk and dairy products. Serratia marcescens was streaked onto spirit blue agar medium, and lipolytic activity was detected after 6 h at 30 degrees C and after 12 h at 6 degrees C. The extracellular crude lipase was collected after inoculation of the organism into nutrient broth and then into skim milk. The crude lipase was purified to homogeneity by ion-exchange chromatography and gel filtration. The purified lipase had a final recovered activity of 45.42%. Its molecular mass was estimated by SDS-PAGE assay to be 52 kDa. The purified lipase was characterized; the optimum pH was likely between 8 and 9 and showed about 70% of its activity at pH 6.6. The enzyme was very stable at pH 8 and lost about 30% of its activity after holding for 24 h at 4 degrees C in buffer of pH 6.6. The optimum temperature was observed at 37 degrees C and exhibited high activity at 5 degrees C. The thermal inactivation of S. marcescens lipase was more obvious at 80 degrees C; it retained about 15% of its original activity at 80 degrees C and was completely inactivated after heating at 90 degrees C for 5 min. Under optimum conditions, activity of the enzyme was maximum after 6 min. The Michaelis-Menten constant was 1.35 mM on tributyrin. The enzyme was inhibited by a concentration more than 6.25mM. Purified lipase was not as heat-stable as other lipases from psychrotrophs, but it retained high activity at 5 degrees C. At pH 6.6, the pH of milk, purified lipase showed some activity and stability. Also, the organism demonstrated lipolytic activity at 6 degrees C after 12 h. Therefore, S. marcescens and its lipase were considered to cause flavor impairment during cold storage of milk and dairy products.
With its theoretical basis firmly established in molecular evolutionary and population genetics, the comparative DNA and protein
sequence analysis plays a central role in reconstructing the evolutionary histories of species and multigene families, estimating
rates of molecular evolution, and inferring the nature and extent of selective forces shaping the evolution of genes and genomes.
The scope of these investigations has now expanded greatly owing to the development of high-throughput sequencing techniques
and novel statistical and computational methods. These methods require easy-to-use computer programs. One such effort has
been to produce Molecular Evolutionary Genetics Analysis (MEGA) software, with its focus on facilitating the exploration and
analysis of the DNA and protein sequence variation from an evolutionary perspective. Currently in its third major release,
MEGA3 contains facilities for automatic and manual sequence alignment, web-based mining of databases, inference of the phylogenetic
trees, estimation of evolutionary distances and testing evolutionary hypotheses. This paper provides an overview of the statistical
methods, computational tools, and visual exploration modules for data input and the results obtainable in MEGA.
In greenhouse experiments, plant growth-promoting rhizobacteria (PGPR) Serratia marcescens NBRI1213 was evaluated for plant growth promotion and biologic control of foot and root rot of betelvine caused by Phytophthora nicotianae. Bacterization of betelvine (Piper betle L.) cuttings with S. marcescens NBRI1213 induced phenylalanine ammonia-lyase, peroxidase, and polyphenoloxidase activities in leaf and root. Qualitative and quantitative estimation of phenolic compounds was done through high-performance liquid chromatography (HPLC) in leaf and root of betelvine after treatment with S. marcescens NBRI1213 and infection by P. nicotianae. Major phenolics detected were gallic, protocatechuic, chlorogenic, caffeic, ferulic, and ellagic acids by comparison of their retention time with standards through HPLC. In all of the treated plants, synthesis of phenolic compounds was enhanced compared with control. Maximum accumulation of phenolics was increased in S. marcescens NBRI1213-treated plants infected with P. nicotianae. In a greenhouse test, bacterization using S. marcescens NBRI1213 decreased the number of diseased plants compared with nonbacterized controls. There were significant growth increases in shoot length, shoot dry weight, root length, and root dry weight, averaging 81%, 68%, 152%, and 290%, respectively, greater than untreated controls. This is the first report of PGPR-mediated induction of phenolics for biologic control and their probable role in protecting betelvine against P. nicotianae, an important soil-borne phytopathogenic fungus.
Twenty-three bacterial isolates were screened for their mineral phosphate-solubilizing (MPS) ability on Pikovskaya and National Botanical Research Institute's phosphate (NBRIP) agar. The majority of the isolates exhibited a strong ability to solubilize hydroxyapatite in both solid and liquid media. The solubilization in liquid medium corresponded with a decrease in the pH of the medium. Serratia marcescens GPS-5, known for its biocontrol of late leaf spot in groundnut, emerged as the best solubilizer. S. marcescens GPS-5 was subjected to ethyl methanesulfonate (EMS) mutagenesis, and a total of 1700 mutants, resulting after 45 minutes of exposure, were screened on buffered NBRIP medium for alterations in MPS ability compared with that of the wild type. Seven mutants with increased (increased-MPS mutants) and 6 mutants with decreased (decreased-MPS mutants) MPS ability were isolated. All seven increased-MPS mutants were efficient at solubilizing phosphate in both solid and liquid NBRIP medium. Among the increased-MPS mutants, EMS XVIII Sm-35 showed the maximum (40%) increase in the amount of phosphate released in liquid medium compared with wild-type S. marcescens GPS-5, therefore, it would be a useful microbial inoculant in groundnut cultivation. EMS III Sm W, a nonpigmented mutant, showed the lowest solubilization of phosphate among the 6 decreased-MPS mutants.
A new method called the neighbor-joining method is proposed for reconstructing phylogenetic trees from evolutionary distance data. The principle of this method is to find pairs of operational taxonomic units (OTUs [= neighbors]) that minimize the total branch length at each stage of clustering of OTUs starting with a starlike tree. The branch lengths as well as the topology of a parsimonious tree can quickly be obtained by using this method. Using computer simulation, we studied the efficiency of this method in obtaining the correct unrooted tree in comparison with that of five other tree-making methods: the unweighted pair group method of analysis, Farris's method, Sattath and Tversky's method, Li's method, and Tateno et al.'s modified Farris method. The new, neighbor-joining method and Sattath and Tversky's method are shown to be generally better than the other methods.
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.
~~ ~ ~ Many insects have a cell-free immune system in which small basic proteins called cecropins are the main defence against Gram-negative bacteria. We have earlier shown that an insect pathogenic strain of Serratia marcescens was resistant to insect immunity and that certain mutants resistant to phage 4J become sensitive to cecropins. We have found that protease- deficient mutants with and without resistance to QJ appear to be deficient in the mechanism of protease induction. Three different protease fractions exist and for two of the enzymes we describe a partial purification and characterization. The proteases show pronounced autodegradation which increases with the purity. Both enzymes are only partly affected by EDTA and they are highly toxic to Drosophila melanogaster. All three enzymes destroy cecropins in immune haemolymph from Cecropia pupae. However, in uiuo experiments with different mutants indicate that in Serratia, passive resistance to insect immunity is more important for virulence in Drosophila than the production of proteases which can destroy cecropins.
It has been found that a reagent containing sulphuric acid, ammonium molybdate and ascorbic acid may be used as a single-solution reagent for the determination of phosphate in sea water. Development of the molybdenum-blue colour is complete in 24 h at room temperature and in 30 min at 60° C; the colour is stable for at least 3 days. Beer's law is obeyed closely up to at least 500 μg PO43−-P/1. The salt error is approximately 4% with sea water of chlorinity 19·3%. The interference due to either arsenate or silicate at their concentrations in sea water is negligible.
Plant growth-promoting rhizobacteria (PGPR) are a group of free-living bacteria that colonize the rhizosphere and benefit
the root growth. Bacteria of diverse genera were identified as PGPR of which Bacillus and Pseudomonas spp. are predominant. PGPR exert a direct effect on plant growth by production of phytohormones, solubilization of inorganic
phosphates, increased iron nutrition through iron-chelating siderophores and volatile compounds that affect the plant signaling
pathways. Additionally, by antibiosis, competition for space and nutrients, and induction of systemic resistance in plants
against a broad-spectrum of root and foliar pathogens, PGPR reduce the populations of root pathogens and other deleterious
microorganisms in the rhizosphere, thus benefiting the plant growth. Root colonization, influenced by a number of biotic and
abiotic components, is a limiting factor for the success of PGPR. Diverse reporter genes and nucleic acid-based methods were
developed to track the introduced PGPR in the rhizosphere, and also to determine their metabolic status, and their effect
on the native rhizosphere microbial communities. Quality of the PGPR formulations, in terms of viability and efficacy, determines
their large-scale adoption at the end-user level. We discuss the importance of PGPR in sustainable agriculture with special
reference to the mechanisms involved in their action and factors affecting their efficacy, along with the possibilities for
their improvement.
The role of organic acids in the mobilization of plant nutrients from the rhizosphere was assessed in seven contrasting soil types. The results indicated that malate was poor at mobilizing micronutrients from all the test soils, whilst citrate was capable of mobilizing significant quantities. Citrate was also capable of mobilizing P from one soil which possessed a large Ca-P fraction. This mobilization of P was due to both the complexing action of the citrate anion and due to the dissolution properties of the protons released from citric acid upon equilibrium with the soil solution. The reaction of citrate with cations was found to be near instantaneous with significant absorption to the solid phase in some soils at low concentrations. Soil decomposition studies indicated that citrate was rapidly broken down in organic soils but was more resistant to degradation in subsoil horizons. It was concluded that organic acids can be expected to be of little consequence in nutrient mobilization from high pH soils, whilst in acid soils they may be involved both in a more general mechanism for micronutrient uptake or as a potential Al detoxification mechanism.
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.RésuméUne méthode spectrophotométrique est décrite pour le dosage du phosphate dans l'eau de mer, an moyen de molybdate d'ammonium, en présence d'acide ascorbique et d'antimoinc. Il se forme rapidement un composé violet bleu, renfermant antimoine et phosphore dans un rapport atomique de 1:1.ZusammenfassungBeschreibung einer Methode zur Bestimmung von Phosphat in Mecrwasser mit Hilfe von Ammoniummolybdat in Gegenwart von Ascorbinsäure und Antimon. Der gebildete blau-violette Komplex wird spektrophotometrisch gemessen.
Inhibition of root cell energy metabolism is suggested to be responsible for potato yield reductions in short potato-rotation soils. Hydrogen cyanide is the microbial metabolile possibly involved in inhibition of energy metabolism. This is supported by the following observations: (1) approximately 50% of potato rhizosphere pseudomonads was shown to produce cyanide in vitro; (2) 5 μM HCN inhibited cytochrome oxidase respiration by at least 40% in intact potato roots in vitro; (3) cyanide production in vitro by Pseudomonas sp. isolate WCS361 depended on the Fe3+ concentration of the medium. Growth promoting fluorescent Pseudomonas spp isolates WCS374 and WCS358 did not produce cyanide in vitro. A hypothesis, that potato plant growth is depressed in short potato rotation soils by the microbial production of cyanide in the rhizosphere is discussed. In such soils, bacteria producing specific siderophores increase growth by competing with cyanide-producing organisms for Fe3+.
The increasing environmental concern about chemical surfactants triggers attention to microbial-derived surface-active compounds essentially due to their low toxicity and biodegradable nature. At present, biosurfactants are predominantly used in remediation of pollutants; however, they show potential applications in many sectors of food industry. Associated with emulsion forming and stabilization, antiadhesive and antimicrobial activities are some properties of biosurfactants, which could be explored in food processing and formulation. Potential applications of microbial surfactants in food area and the use of agroindustrial wastes as alternative substrates for their production are discussed.
A new method called the neighbor-joining method is proposed for reconstructing phylogenetic trees from evolutionary distance data. The principle of this method is to find pairs of operational taxonomic units (OTUs [= neighbors]) that minimize the total branch length at each stage of clustering of OTUs starting with a starlike tree. The branch lengths as well as the topology of a parsimonious tree can quickly be obtained by using this method. Using computer simulation, we studied the efficiency of this method in obtaining the correct unrooted tree in comparison with that of five other tree-making methods: the unweighted pair group method of analysis, Farris's method, Sattath and Tversky's method, Li's method, and Tateno et al.'s modified Farris method. The new, neighbor-joining method and Sattath and Tversky's method are shown to be generally better than the other methods.
Plasmid pRD1, an R plasmid of the P incompatibility group which carries his and nif genes from Klebsiella pneumoniae in addition to drug resistance markers derived from RP4, was transferred to His- mutants of Serratia marcescens, Erwinia herbicola and Proteus mirabilis. His+ transconjugants were obtained at low but different frequencies according to recipient genus. Transconjugants all acquired the drug resistance, and were Nif+ in S. marcescens and E. herbicola, having acetylene-reducing activities of the same order of magnitude as the parent K. pneumoniae and fixing 15N2. No evidence for nif expression in P. mirabilis transconjugants was obtained though the nif genes were present.
Some simple formulae were obtained which enable us to estimate evolutionary distances in terms of the number of nucleotide substitutions (and, also, the evolutionary rates when the divergence times are known). In comparing a pair of nucleotide sequences, we distinguish two types of differences; if homologous sites are occupied by different nucleotide bases but both are purines or both pyrimidines, the difference is called type I (or "transition" type), while, if one of the two is a purine and the other is a pyrimidine, the difference is called type II (or "transversion" type). Letting P and Q be respectively the fractions of nucleotide sites showing type I and type II differences between two sequences compared, then the evolutionary distance per site is K = -(1/2) ln [(1-2P-Q) square root of 1-2Q]. The evolutionary rate per year is then given by k = K/(2T), where T is the time since the divergence of the two sequences. If only the third codon positions are compared, the synonymous component of the evolutionary base substitutions per site is estimated by K'S = -(1/2) ln (1-2P-Q). Also, formulae for standard errors were obtained. Some examples were worked out using reported globin sequences to show that synonymous substitutions occur at much higher rates than amino acid-altering substitutions in evolution.
An efficient protocol was developed for qualitative screening of phosphate-solubilizing bacteria, based upon visual observation. Our results indicate that, by using our formulation containing bromophenol blue, it is possible to quickly screen on a qualitative basis the phosphate-solubilizing bacteria. Qualitative analysis of the phosphate solubilized by various groups correlated well with grouping based upon quantitative analysis of bacteria isolated from soil, effect of carbon, nitrogen, salts, and phosphate solubilization-defective transposon mutants. However, unlike quantitative analysis methods that involve time-consuming biochemical procedures, the time for screening phosphate-solubilizing bacteria is significantly reduced by using our simple protocol. Therefore, it is envisaged that usage of this formulation based upon qualitative analysis will be salutary for the quick screening of phosphate-solubilizing bacteria. Our results indicate that the formulation can also be used as a quality control test for expeditiously screening the commercial bioinoculant preparations, based on phosphate solubilizers.
The vast surface of the plant axis, stretching from root tips occasionally buried deeply in anoxic sediment, to apical meristems held far aloft, provides an extraordinarily diverse habitat for microorganisms. Each zone has to a greater or lesser extent its own cohort of microorganisms, in aggregate comprising representatives from all three primary domains of life-Bacteria, Archaea, and Eucarya. While the plant sets the stage for its microbial inhabitants, they, in turn, have established varied relationships with their large partner. These associations range from relatively inconsequential (transient epiphytic saprophytes) to substantial (epiphytic commensals, mutualistic symbionts, endophytes, or pathogens). Through recent technological breakthroughs, a much better perspective is beginning to emerge on the nature of these relationships, but still relatively little is known about the role of epiphytic microbial associations in the life of the plant.
Plant growth promoting rhizobacteria (PGPR) are commonly used as inoculants for improving the growth and yield of agricultural crops, however screening for the selection of effective PGPR strains is very critical. This study focuses on the screening of effective PGPR strains on the basis of their potential for in vitro auxin production and plant growth promoting activity under gnotobiotic conditions.
A large number of bacteria were isolated from the rhizosphere soil of wheat plants grown at different sites. Thirty isolates showing prolific growth on agar medium were selected and evaluated for their potential to produce auxins in vitro. Colorimetric analysis showed variable amount of auxins (ranging from 1.1 to 12.1 mg l-1) produced by the rhizobacteria in vitro and amendment of the culture media with l-tryptophan (l-TRP), further stimulated auxin biosynthesis (ranging from 1.8 to 24.8 mg l-1). HPLC analysis confirmed the presence of indole acetic acid (IAA) and indole acetamide (IAM) as the major auxins in the culture filtrates of these rhizobacteria. A series of laboratory experiments conducted on two cv. of wheat under gnotobiotic (axenic) conditions demonstrated increases in root elongation (up to 17.3%), root dry weight (up to 13.5%), shoot elongation (up to 37.7%) and shoot dry weight (up to 36.3%) of inoculated wheat seedlings. Linear positive correlation (r = 0.99) between in vitro auxin production and increase in growth parameters of inoculated seeds was found. Based upon auxin biosynthesis and growth-promoting activity, four isolates were selected and designated as plant growth-promoting rhizobacteria (PGPR). Auxin biosynthesis in sterilized vs nonsterilized soil inoculated with selected PGPR was also monitored that revealed superiority of the selected PGPR over indigenous microflora. Peat-based seed inoculation with selected PGPR isolates exhibited stimulatory effects on grain yields of tested wheat cv. in pot (up to 14.7% increase over control) and field experiments (up to 27.5% increase over control); however, the response varied with cv. and PGPR strains.
It was concluded that the strain, which produced the highest amount of auxins in nonsterilized soil, also caused maximum increase in growth and yield of both the wheat cv.
This study suggested that potential for auxin biosynthesis by rhizobacteria could be used as a tool for the screening of effective PGPR strains.
Pest Management: Biologically Based Technologies
- J.W. Kloepper
- S. Tuzun
- L. Liu
- G. Wei
Cold-tolerant Serratia marcescens ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology
- G Selvakumar
G. Selvakumar et al.
Cold-tolerant Serratia marcescens
ª 2007 The Authors
Journal compilation ª 2007 The Society for Applied Microbiology, Letters in Applied Microbiology 46 (2008) 171–175
Microbiological methods
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Collins, C.H. and Lyne, P.M.(1980) Microbiological methods.
London: Butterworth and Co.
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Jackson, M. L.(1973) Soil chemical analysis pp. 25-214. New
Delhi: Prentice Hall of India Pvt Ltd.