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Antagonism of Actinobacteria against fungal plant pathogens a) Macrophomina phaseolina b) Sclerotium rolfsii c) Rhizoctonia solani d) Fusarium oxysporum
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Biological control of plant pathogens is assuming increasing importance in organic and low input sustainable agriculture. Forty one Actinobacterial strains isolated from the arid, semi arid and humid regions of Rajasthan, Karnataka, Andhra Pradesh in India were tested for their antagonism to four plant pathogenic fungi viz., Macrophomina phaseolina...
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Sheath blight caused by Rhizoctonia solani results in severe yield reduction in rice. Plant genotypes highly resistant to rice sheath blight are not available, which avails opportunity for the exploration of microbial resources for disease management. Actinobacteria were purified from rhizosphere samples to identify potential biocontrol agents. Six...
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... La rizosfera del cerco vivo de Swinglea glutinosa (Blanco) Merr. es un ambiente con alteraciones antropogénicas debido al suministro de fertilizantes que representan fuentes de nitrógeno adicionales para la microbiota asociada con las raíces de estos arbustos; este suelo en el momento del muestreo, presentó menores niveles de humedad que las demás muestras, y esto puede dar ventajas competitivas a algunas bacterias filamentosas sobre otro tipo de bacterias (Radha et al., 2017). ...
Contextualización: Las hidrolasas son algunas de las enzimas que más se usan en diferentes procesos industriales y se pueden obtener a partir de microorganismos como bacterias y hongos. Las bacterias filamentosas son un grupo de microorganismos presentes en diversos ambientes y muchas de estas especies producen hidrolasas extracelulares que catalizan la descomposición de compuestos como proteínas y polisacáridos. El género más representativo es Streptomyces, un grupo bacteriano que se encuentra en la mayoría de los suelos y que sintetiza enzimas de interés y los principales antibióticos de origen microbiano. Vacío de conocimiento: La alta diversidad de suelos en el país representa una oportunidad para la bioprospección de microrganismos nativos con potencial enzimático; estos se pueden encontrar en diferentes agroecosistemas poco estudiados y sus capacidades bioquímicas podrían estar asociadas con las condiciones ambientales y nutricionales de los sitios en los que se encuentran. Objetivo: Verificar la presencia de bacterias filamentosas productoras de enzimas hidrolíticas con potencial aplicación industrial, en diferentes tipos de suelo y en un sistema de compostaje. Metodología: Se tomaron muestras de un sistema de compostaje, del suelo de un sendero en un bosque nativo y de las rizosferas de un cerco vivo y de cultivos de hortensias, aguacate, mora y coles. Se aislaron bacterias filamentosas a partir de colonias que presentaran la morfología correspondiente. Las actividades enzimáticas se determinaron usando el método de difusión en disco para cuantificar los halos de hidrólisis en medios con almidón, carboximetilcelulosa, gelatina y aceite de oliva. Resultados y conclusiones: Se obtuvieron 43 aislados de bacterias filamentosas de las cuales 36, 42, 39 y 30 presentaron actividad amilasa, celulasa, gelatinasa y lipasa, respectivamente. En todas las muestras se encontró al menos un aislado con alguna actividad hidrolítica. El sistema de compostaje y la rizosfera del cerco vivo fueron los sitios a partir de los cuales se obtuvieron más aislados bacterianos con mayor actividad, posiblemente relacionada con características como la humedad y la materia orgánica de los suelos de los cuales fueron recuperados.
... Another high-level balance, b459, shows displacement of Micrococcales by a large clade of Actinobacteria. Many representatives of Actinobacteria are drought-tolerant and inhabit arid areas [61]. Among them, there are the PGPR bacteria that mitigate water stress for plants [62,63], while Micrococcales are known as bacteria that inhabit soil as well as water [64]. ...
Drought and heavy metals seriously affect plant growth and the biodiversity of the associated rhizosphere microbiomes, which, in turn, could be involved in the adaptation of plants to these environmental stresses. Rhizosphere soil was collected from a three-factor pot experiment, where pea line SGE and its Cd-tolerant mutant SGECdt were cultivated under both optimal and limited water conditions and treated with a toxic Cd concentration. The taxonomic structure of the prokaryotic rhizosphere microbiome was analyzed with the high-throughput sequencing of 16S rRNA amplicon libraries. A permutation test demonstrated statistically significant effects of Cd and water stress but not of pea genotype on the rhizosphere microbiome structure. Phylogenetic isometric log-ratio data transformation identified the taxonomic balances that were affected by abiotic factors and pea genotypes. A small number of significant (log ratio [−3.0:+3.0]) and phylogenetically deep balances characterized water stress, while a larger number of weak (log ratio [−0.8:+0.8]) phylogenetically lower balances described the influence of the plant genotype. Stress caused by cadmium took on an intermediate position. The main conclusion of the study is that the most powerful factor affecting the rhizosphere microbiome was water stress, and the weakest factor was plant genotype since it demonstrated a very weak transformation of the taxonomic structure of rhizosphere microbiomes in terms of alpha diversity indices, beta diversity, and the log ratio values of taxonomic balances.
... Above that Actinobacteria participated in many biotic interactions so might be suppressed by fungal pathogen or facilitated by the assembly of microbes or plants, for which Actinobacteria mediated available sources of energy by degradation of resistant compounds (Radha et al., 2017). Cooperation or competition of Actinobacteria with other microbial community members might be mediated by secondary metabolites production, however in nature has been scarcely investigated (Miao and Davies, 2010). ...
Actinobacteria are important bacterial group participating in various ecosystem processes particularly in the decomposition of complex organic compounds. Their abilities enable them to surviving in harsh conditions of oligotrophic habitats like lakes, deserts, cave walls or recalcitrant and resistant litter in soil, where Actinobacteria often dominate. Although certain biotic and abiotic factors were recognized to modulate Actinobacteria incidence in such habitats, the influence of anthropogenic pressure on their communities is scarcely known. The main objective of this thesis is therefore to determine differences of Actinobacteria communities under the direct (the human visitors changing microenvironment of caves, part 1) and indirect (climate change factors like altered precipitation or plant litter quality, part 2) anthropogenic influence in two habitats, plant litter in soil and cave walls, where Actinobacteria play important roles and dominate. In a first part of the thesis we monitored Actinobacteria communities in French limestone caves walls differently affected by humans (pristine versus anthropized caves). For identification of important species like potential pathogens or pigments producing Actinobacteria using amplicon sequencing of environmental DNA (Illumina MiSeq), we firstly used a molecular marker gene hsp65 coding for heat shock protein specific for Actinobacteria. Special attention was payed to anthropogenically most affected Lascaux Cave with Paleolithic paintings. There, a comparison of different rooms differently affected by a human-derived intervention as well as between visual dark marks and unmarked areas on the wall paintings were compared (paper I). In the second part, we monitored litter Actinobacteria communities during a decomposition process under manipulated precipitation (paper IV), on different litter type, quality and origin (papers II, III, IV) in different forests including Mediterranean oak and pine forests (paper IV), mountainous spruce and beech forests (paper III), a beech temperate forest (paper II)) and also one grassland (paper II). Our results show that Actinobacteria communities were strongly dependent to anthropized/pristine status of caves (Part 1) as well as climatic and litter quality changes during the decomposition (Part 2). In caves (Part 1), Actinobacteria community structure indicated the anthropogenic disturbance, because typical pristine and anthropogenic taxa identified according to the hsp65 marker were recovered in relation to an anthropization status (paper I). During decomposition (part 2), we found that Actinobacteria were i) affected by litter type regardless its origin but their dominance on recalcitrant litter type did not result in faster decomposition (papers II, III, IV), ii) not directly affected by climatic conditions (paper III, IV) but were site-specific (papers II, III, IV) with a potential to dominate introduced coniferous forests (papers III, IV), and iii) in decomposition process had opposite strategies to fungi, since were influenced by different conditions than fungi (papers II, III, IV). Overall, Actinobacteria respond to anthropogenic pressure on a community and species level and are also able to adapt to harsh conditions and thus, these changes leading to Actinobacteria persistence in ecosystems.
Soil-borne pathogens have economic significance regarding the damage they cause to crop production worldwide. Arid lands are even more susceptible to soil-borne pathogens damage due to climate extremes such as high temperature and evapotranspiration to precipitation ratio that limits the diversity of crops. More so, some soil-borne pathogens are highly adapted to arid lands' high soil temperature and water limitations. Chemical controls like fungicides and bactericides are widely used in managing soil-borne diseases, but they come at a significant environmental, health, and agricultural cost. On the other hand, biological control of soil-borne pathogens is relatively environment-friendly, safe, has no reported effect on human and animal health, and can improve soil health for optimum ecosystem functioning. Thus, this review presents an overview of soil-borne pathogens infestation in arid lands and the potential of using biological control agents (BCAs) in managing plant disease outbreaks. Some common pathogens in arid lands include Fusarium spp. (pathogenic), Pythium spp., Rhizoctonia solani, and Meloidogyne incognita. Investigations have, however, revealed effective BCAs against soil-borne pathogens, and some examples include Bacillus cereus, Streptomyces atrovirens, Phlebiopsis gigantea, Pseudomonas putida, Trichoderma harzianum, Pythium oligandrum, and Enterobacter amnigenus. The most common mechanisms used by BCAs for controlling soil-borne pathogens include antibiosis, induced systemic resistance, parasitism (mycoparasitism), antagonism, competition for nutrients and space, and indirect plant growth promotion. Recent advances in molecular biology, such as metabarcoding and biomarker transformation, offer promising ways to increase the success rates with the use of BCAs under field conditions. This study suggests that the effectiveness of BCAs can be further enhanced with the addition of soil organic amendments coupled with the cultivation of arid lands adapted crops such as agave and Opuntia spp.
To explore the in vivo and in vitro plant growth promoting activities, biocatalytic potential, and antimicrobial activity of salt tolerance rhizoactinobacteria, rhizospheric soil of a halotolerant plant Saueda maritima L. was collected from Rann of Tiker, near Little Rann of Kutch, Gujarat (India). The morphology analysis of the isolated strain TSm39 revealed that the strain belonged to the phylum actinobacteria, as it was stained Gram-positive, displayed filamentous growth, showed spore formation and red pigment production on starch casein agar (SCA). It was identified as Georgenia soli based on 16S rRNA gene sequencing. The Georgenia soli strain TSm39 secreted extracellular amylase, pectinase, and protease. It showed in vitro plant growth-promoting (PGP) activities such as indole acetic acid (IAA) production, siderophore production, ammonia production, and phosphate solubilization. In vivo plant growth-promoting traits of strain TSm39 revealed 30% seed germination on water agar and vigor index 374.4. Additionally, a significant increase (p ≤ 0.05) was found in growth parameters such as root length (16.1 ± 0.22), shoot length (15.2 ± 0.17), the fresh weight (g), and dry weight (g) of the roots (0.43 ± 0.42 and 0.32 ± 0.12), shoots (0.62 ± 0.41 and 0.13 ± 0.03), and leaves (0.42 ± 0.161 and 0.14 ± 0.42) in treated seeds of Vigna radiata L. plant with the strain TSm39 compared to control. The antibiotic susceptibility profile revealed resistance of the strain TSm39 to erythromycin, ampicillin, tetracycline, and oxacillin, while it displayed maximum sensitivity to vancomycin (40 ± 0.72), chloramphenicol (40 ± 0.61), clarithromycin (40 ± 1.30), azithromycin (39 ± 0.42), and least sensitivity to teicoplanin (15 ± 0.15). Moreover, the antimicrobial activity of the strain TSm39 was observed against Gram’s positive and Gram’s negative microorganisms such as Shigella, Proteus vulgaris, and Bacillus subtilis. These findings indicated that the Georgenia soli strain TSm39 has multiple plant-growth-promoting properties and biocatalytic potential that signifies its agricultural applications in the enhancement of crop yield and quality and would protect the plant against plant pathogens.
