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Isolation, identification, and antifungal activity of a macrolide antibiotic, oligomycin A, produced by Streptomyces libani
Abstract
The antibiotic As1A, strongly inhibitory to Phytophthora capsici Leonian in vitro and in vivo, was isolated from the broth culture of Streptomyces libani Baldacci and Grein using various chromatographic procedures. The molecular formula of the antibiotic As1A was deduced to be C45H74O11 (M+H, m/z 791.5307) by high resolution fast atom bombardment - mass spectroscopy. The analysis of 1H-NMR (nuclear magnetic resonance) and 13C-NMR spectroscopy, DEPT experiment, and two-dimensional NMR spectral data revealed that the antibiotic is a macrolide antibiotic having a 26-membered α, β-unsaturated macrolactone ring with a conjugated diene fused to a bicyclic spiroketal. Based on the comparison of NMR data and other chemical properties, the antibiotic As1A turned out to have the same structure as oligomycin A. The antibiotic As1A showed a high level of inhibitory activity against Botrytis cinerea Pers.: Pers., Cladosporium cucumerinum Ellis and Arthur, Colletotrichum lagenarium (C.P. Robin) Berkhout, Magnaporthe grisea (Herb.) Barr, and P. capsici, ranging from 3 to 5 μg·mL-1 of MICs. However, no antimicrobial activity was found against yeasts and bacteria. In further evaluation under greenhouse conditions, developments of the Phytophthora disease, anthracnose, and leaf blast were markedly inhibited on pepper (Capsicum annuum L. cv. Hanbyul), cucumber (Cucumis sativus L. cv. Baekrokdadaki), and rice (Oryza sativa L. cv. Nakdong) plants by treatments with the antibiotic As1A, respectively. Control efficacies of the antibiotic As1A against these plant diseases were in general similar to those of metalaxyl, chlorothalonil, and tricyclazole. The antibiotic As1A did not show any phytotoxicity on pepper, cucumber, and rice plants even at 500 μg·mL-1.
... Blasticidin S and kasugamycin produced by S. griseochromogenes and S. kasugaensis, respectively, also suppressed rice blast fungus by 95% [157]. Oligomycin A, polyoxin A, polyoxin B, and cyclo (Lleucyl-L prolyl) synthesized by Streptomyces spp., showed strong antifungal activities against the rice blast fungus MoO at 3.0, 6.25, 6.25 and 2.5 mg/ml, respectively [78,160,163]. In an in vitro experiment, we have found that oligomycin B and F, synthesized by Streptomyces spp. ...
... produces oligomycins, which interrupt ATP synthase by blocking the proton channel required for oxidative phosphorylation of ADP to ATP [214]. It has shown efficacy against M. oryzae MoO and M. oryzae MoT by suppressing mycelial growth [160,162]. Oligomycin A extracted from marine Streptomyces has been reported as a motility inhibitor and lysis inducer of peronosporomycete zoospores [215,216]. ...
Blast diseases, caused by the fungal pathogen Magnaporthe oryzae, are among the most destructive diseases that occur on at least 50 species of grasses, including cultivated cereals wheat, and rice. Although fungicidal control of blast diseases has widely been researched, development of resistance of the pathogen against commercially available products makes this approach unreliable. Novel approaches such as the application of biopesticides against the blast fungus are needed for sustainable management of this economically important disease. Antagonistic microorganisms , such as fungi and probiotic bacteria from diverse taxonomic genera were found to suppress blast fungi both in vitro and in vivo. Various classes of secondary metabolites, such as alkaloids, phenolics, and terpenoids of plant and microbial origin significantly inhibit fungal growth and may also be effective in managing blast diseases. Common modes of action of microbial biocontrol agents include: antibiosis, production of lytic enzymes, induction of systemic resistance in host plant, and competition for nutrients or space. However, the precise mechanism of biocontrol of the blast fungus by antagonistic microorganisms and/or their bioactive secondary metabolites is not well understood. Commercial formulations of biocontrol agents and bio-active natural products could be cost-effective and sustainable but their availability at this time is extremely limited. This review updates our knowledge on the infection pathway of the wheat blast fungus, catalogs naturally occurring biocontrol agents that may be effective against blast diseases, and discusses their role in sustainable management of the disease. ARTICLE HISTORY
... The soil-inhabiting bacteria, particularly Streptomyces genus, are able to produce diverse bioactive compounds and are used for producing metabolites, such as peptides, macrolides, aminoglycosides, polyenes, polyethers, tetracyclines, and βˍlactams with antimicrobial activity [16,26,27]. In several studies, the production of antifungal metabolites, such as bafilomycin A1, oligomycin, geldanamycin, nikkomycin, and reveromycin A and B, has been reported by various strains to belong to the genus of Streptomyces [27][28][29]. Most of these compounds have polyketide and peptide structures and have inhibitory activity against filamentous fungi. ...
... The antagonistic bacteria were identified as Streptomyces libani, Streptomyces angustmyceticus, Bacillus subtilis, and Sphingopyxis sp. As these bacteria have been reported to produce antifungal metabolites, various culture conditions were tested to optimize the production of antifungal metabolites by actinomycetes [28,30,31,32]. ...
Background and purpose:
Soil bacteria have extreme population diversity among natural sources and are able to produce a wide array of antifungal metabolites. This study aimed to isolate and identify the bioactive metabolite-producing bacteria from forest soils and evaluate their antimicrobial potent against some pathogenic organisms.
Materials and methods:
In this study, soil samples were screened for antifungal activity against Aspergillus fumigatus on glucose-yeast extract (GY) agar using a visual agar plate assay method. All growing bacteria were examined for antifungal activity, and antagonistic bacteria were identified based on 16S ribosomal RNA sequence analysis. For optimization of the production of antifungal bioactive metabolites, inhibitory bacteria were cultured on different culture conditions, including media, pH, temperature, and incubation time.
Results:
In total, 110 bacterial strains were isolated from the forest soils and four species with high antifungal activity were identified as Streptomyces libani, Streptomyces angustmyceticus, Bacillus subtilis, and Sphingopyxis spp. on the basis of 16s ribosomal RNA sequencing. Dichloromethane extract of the starch casein broth culture filtrate of the S. libani (incubated at 30° C for five days) showed strong antifungal activity against A. fumigatus, Aspergillus niger, and Aspergillus flavus.
Conclusion:
Based on the results, forest soils contain organisms with antifungal activity and could be considered as a good source for novel antifungal metabolites as effective and safe therapeutics.
... The antibiotic Oligomycin A was first isolated from S. diastatochromogenes and was found to be active against several other phytopathogenic fungi in addition to M. oryzae such Frontiers in Microbiology | www.frontiersin.orgas Botrytis cinerea, Cladosporium cucumerinum, Colletotrichum lagenarium, Phytophthora capsici, Alternaria alternata, and Aspergillus niger (Smith et al., 1954; Kim et al., 1999; Yang et al., 2010). Oligomycin A's ability to control the development of rice blast was evaluated in the greenhouse and the results showed that rice plants treated with Oligomycin A (50 µg/mL) had reduced lesions. ...
... Oligomycin A's ability to control the development of rice blast was evaluated in the greenhouse and the results showed that rice plants treated with Oligomycin A (50 µg/mL) had reduced lesions. When the concentration of Oligomycin A was increased up to 500 µg/mL, the rice plants did not show any rice blast disease symptoms (Kim et al., 1999). Rapamycin—also known as Sirolimus—was initially isolated from S. hygroscopicus (Sehgal et al., 1975; Sehgal, 1998). ...
Rice is a staple food source for more than three billion people worldwide. However, rice is vulnerable to diseases, the most destructive among them being rice blast, which is caused by the fungus Magnaporthe oryzae (anamorph Pyricularia oryzae). This fungus attacks rice plants at all stages of development, causing annual losses of approximately 10–30% in various rice producing regions. Synthetic fungicides are often able to effectively control plant diseases, but some fungicides result in serious environmental and health problems. Therefore, there is growing interest in discovering and developing new, improved fungicides based on natural products as well as introducing alternative measures such as biocontrol agents to manage plant diseases. Streptomyces bacteria appear to be promising biocontrol agents against a wide range of phytopathogenic fungi, which is not surprising given their ability to produce various bioactive compounds. This review provides insight into the biocontrol potential of Streptomyces against the rice blast fungus, M. oryzae. The ability of various Streptomyces spp. to act as biocontrol agents of rice blast disease has been studied by researchers under both laboratory and greenhouse/growth chamber conditions. Laboratory studies have shown that Streptomyces exhibit inhibitory activity against M. oryzae. In greenhouse studies, infected rice seedlings treated with Streptomyces resulted in up to 88.3% disease reduction of rice blast. Studies clearly show that Streptomyces spp. have the potential to be used as highly effective biocontrol agents against rice blast disease; however, the efficacy of any biocontrol agent may be affected by several factors including environmental conditions and methods of application. In order to fully exploit their potential, further studies on the isolation, formulation and application methods of Streptomyces along with field experiments are required to establish them as effective biocontrol agents.
... This group of antibiotics is active e.g. against Aspergillus niger, Candida albicans and Cryptococcus humicolus (Lysenkova et al. 2010). Oligomycins A and C have been reported as inhibitory metabolites against some major phytopathogens including Phytophthora capsici (peronosporomycete), however, and are inactive against yeasts and bacteria (Kim, Moon and Hwang 1999;Yang et al. 2010). It is of considerable scientific interest that oligomycins inhibit ATP synthesis by affecting oxidative phosphorylation in mitochondria (Smith, Peterson and McCoy 1954). ...
... Its activity against Proteus vulgaris, Bacillus subtilis, Salmonella typhosa, Shigella sonnei, Escherichia coli and Staphylococcus aureus with MIC values ranging from 100 to 400 μg mL −1 has been reported (Sato et al. 1982). Likewise, pamamycin and oligomycins are not specific inhibitors of peronosporomycete phytopathogens but have also a broad range of antimicrobial activities (Kondo et al. 1988;Kim, Moon and Hwang 1999). Literature data for their antimicrobial spectra are given in the Table S3 (Supporting Information). ...
Four antibiotics (pamamycin, oligomycin A, oligomycin B, and echinosporin) were isolated and characterized from the fermentation broth of the marine Streptomyces strains B8496 and B8739. Bioassays revealed that each of these compounds impaired motility and caused subsequent lysis of P. viticola zoospores in a dose- and time-dependent manner. Pamamycin displayed the strongest motility inhibitory and lytic activities (IC50 0.1 μg mL−1) followed by oligomycin B (IC50 0.15 and 0.2 μg mL−1), and oligomycin F (IC50 0.3 and 0.5 μg mL−1). Oligomycin A and echinosporin also showed motility inhibitory activities against the zoospores with IC50 values of 3.0 and 10.0 μg mL−1, respectively. This is the first report of motility inhibitory and lytic activities of these antibiotics against zoospores of a phytopathogenic peronosporomycete. Structures of all the isolated compounds were determined based on detailed spectroscopic analysis.
... This is especially obvious for the example of Polyversum. A stimulating effect [22,27,68] and inhibition of growth [27,29,69,70] and plant cell death [71] have been documented in diverse BCAs. As mentioned by Blom et al. [68], the resultant quality of interaction between microorganism and plant may be dependent on the concentration of microbial dosage; their release of some volatile components and their concentration alone also strongly depend on the nutritional richness of the cultivating media [25,31,68,71,72]. ...
A comparison of the ability of commercially produced biological control agents—Contans, Gliorex, Hirundo, Polyversum, Prometheus, Clonoplus, Integral Pro and Xilon GR, completed with an isolate of Clonostachys rosea and of Pseudomonas sp.—to protect strawberry plants against Phytophthora cactorum was performed. The experiment was performed on strawberry cultivars Sonata, Karmen, and Wendy—cultivated in a cultivating room and greenhouse. The health of plants was affected negatively by the pathogen in all variants of biological agents used, but differences were seen in the rates of this decrease. The results revealed the ability of some tested agents to improve the growth of plants in the absence of the pathogen; the preparation Polyversum (Pythium oligandrum) was the most beneficial, in both the presence and absence of the pathogen. Contrarily, some agents alone decreased the health of plants; Integral Pro (Bacillus subtillis) and a strain of Pseudomonas sp. caused a deterioration in the health of the plants, even in the absence of a pathogen. The results of our analysis demonstrate the varied usefulness of all agents under unified environmental conditions; their effect seems to be dependent on the conditions and on the combination of the genotypes of all three participants in the interaction: plant–pathogen–antagonist.
... Several studies have been performed for testing of the various compounds produced by Streptomyces on M. oryzae. The antibiotic Oligomycin A was first isolated from Streptomyces diastatochromogenes and was controlling several other plant pathogenic fungi such as Botrytis cinerea, Cladosporium cucumerinum, Colletotrichum lagenarium, Phytophthora capsici, Alternaria alternata, and Aspergillus niger in addition to M. oryzae [1][2][3]. Other compounds such as Pyrroles (Pyrrolo [1,2-a] pyrazine-1,4-dione, hexahydro-) are commonly found in various actinobacterial species [4,5]. ...
Objective: The aims of the present study were to screen the actinobacteria with high potential ability to produce secondary metabolites that have inhibitory activity against plant pathogenic fungi, Magnaporthe oryzae. Production of secondary metabolites was analysis by thin-layer chromatography and bioautography assay. Methods: Screening and selection of potential Streptomyces sp. morphological, cultural, physiological, and biochemical characterization of the screened isolate was carried out. Antifungal compound was confirmed by bioautography assay. Results: Bioautography method use in this study was found to be antifungal fraction from the crude extract. Antifungal secondary metabolites can be readily located on the plates by observing clear zones where active compounds inhibit fungal growth. Conclusion: The bioautography assay shows that this isolates can produce antifungal compound. Therefore, this isolate proves to be a promising microbe which can be further studied for its applications a biocontrol agent against rice blast fungi.
... The involvement of Streptomyces in the parasitic life and elimination of pathogenic fungal spores has been confirmed in the literature. It is known that Streptomyces species can inhibit the growth of fungal hyphae by producing various enzymes and metabolites, such as bafilomycin, concanamycin A, reveromycin A and B, blasticidin A, aflastatin A and B, oligomycin, geldanamycin, butyrolactone, cellulase and glucanase (Kim et al. 1999;Jun-Tao et al. 2013;Pan et al. 2015;Lyu et al. 2017;Khebizi et al. 2018). Streptomyces caverenesis produces a combination of toxic macrolide antibiotics, called bafilomycin (B1 and C1). ...
Aims:
This study aimed to investigate the mechanism of antifungal action of Streptomyces libani dichloromethane extract fraction A (DCEFA) against Aspergillus fumigatus and the host cytotoxicity.
Methods and results:
DCEFA was purified from S. libani by autobiography and showed strong antifungal activity against A. fumigatus. A combination of electron microscopy, cell permeability assays, total oxidant status (TOS) assay, cell cytotoxicity assay, and hemolysis activity were carried out to determine the target site of DCEFA. Exposure of A. fumigatus to DCEFA caused the damage to membranous cellular structures and increased release of cellular materials, potassium ions and TOS production. DCEFA was bound to ergosterol but did not affect fungal cell wall and ergosterol content. DCEFA did not show any obvious hemolytic activity for RBCs and toxicity against HEK-293 cell line.
Conclusions:
DCEFA may inhibit A. fumigatus growth by targeting fungal cell membrane which results in the leakage of potassium ions and other cellular components, TOS production and final cell death.
Significance:
and Impact of the Study DCEFA of S. libani could be considered as a potential source of novel antifungals which may be useful for drug development against Aspergillus fumigatus as a life-threatening human pathogen.
... Many reports reveal that bacteria produce of antifungal metabolites in vitro which also showed activity in vivo (Akhtar and Siddiqui 2010). Numerous studies are present that reveal the presence of metabolites like amphisin, 2,4-diacetylphloroglucinol (DAPG), cyclic lipopeptide butyrolactones, HCN, oligomycin A kanosamine, oomycin A, pyoluterin (Plt), phenazine-1-carboxylic acid (PCA), tropolone, zwittermicin A, pyrrolnitrin (Pln), tensin, viscosinamide, and xanthobaccin, as produced by PGPR (Milner et al. 1996;Whipps 1997;Kang et al. 1998;Kim et al. 1999;Nakayama et al. 1999;Raaijmakers et al. 1999;de Souza et al. 2003;Compant et al. 2005). ...
Plant growth-promoting rhizobacteria (PGPR) play an important role in sustainable agriculture through the improvement of plant growth via different processes like biological nitrogen fixation, phosphate solubilization, siderophore production , and phytohormone synthesis. The use of PGPR is potentially increased in sustainable farming due to its ecofriendly and efficient nature. It is being used as an alternative source to minimize the increasing use of synthetic fertilizers and pesticides. Biofertilizers are the substances containing living microbes, helping to improve plant growth and development. These living microorganisms enhance the nutrient status of soil through the expansion of root surface area, nitrogen fixation, phosphate solubilization, and combination of all these mechanisms. The market of the biofertilizers is expected to reach 3.8$ billion by 2025 from 2$ billion in 2019. Some Pseudomonas species also improve the plant growth through the production of water-soluble vitamins like niacin. PGPR have the potential to work as phyto-stimulators through the production of various phytohormones like indole acetic acid (IAA), cytokinin, gibberellins, and ethylene. But some bacteria and fungi have ability to improve plant growth by restricting the growth of plant pathogens are known as biopesticides. Cyanide biosynthesis, siderophore production, and induction of systemic resistance genes in plants are the different mechanisms for the PGPR to work against the plant pathogens. PGPR can also work as biocontrol agents providing protection to the plants, enhancing the plant growth through the synthesis of antibiotics. The use of the biopesticides is increasing slowly at a rate of 8% annually based on the different types of microbial pesticides.
... Antibiotic production through bacterial system also signifies the metabolic activity of the organism, as the metabolic activity depends on the various environmental factors like pH, temperature, and other various physiological and physiochemical conditions [174][175][176]; however, the activity of antibiotics is also resistant to the various ranges of temperatures and pH [177]. DAPG, phenazine-1carboxylic acid, pyoluterin, viscosinamide, xanthobaccin, oomycin A kanosamine, zwittermycin A, tensin, tropolone, oomycin A, and cyclic lipopeptides are a few antibiotic compounds, which are known to check the phytopathogenecity [173][174][175][178][179][180][181][182][183][184]. Table 2 shows the production of antibiotics by various strains of PGPR. ...
Plant growth‐promoting rhizobacteria (PGPR) are diverse groups of plant‐associated microorganisms, which can reduce the severity or incidence of disease during antagonism among bacteria and soil‐borne pathogens, as well as by influencing a systemic resistance to elicit defense response in host plants. An amalgamation of various strains of PGPR has improved the efficacy by enhancing the systemic resistance opposed to various pathogens affecting the crop. Many PGPR used with seed treatment causes structural improvement of the cell wall and physiological/biochemical changes leading to the synthesis of proteins, peptides, and chemicals occupied in plant defense mechanisms. The major determinants of PGPR‐mediated induced systemic resistance (ISR) are lipopolysaccharides, lipopeptides, siderophores, pyocyanin, antibiotics 2,4‐diacetylphoroglucinol, the volatile 2,3‐butanediol, N‐alkylated benzylamine, and iron‐regulated compounds. Many PGPR inoculants have been commercialized and these inoculants consequently aid in the improvement of crop growth yield and provide effective reinforcement to the crop from disease, whereas other inoculants are used as biofertilizers for native as well as crops growing at diverse extreme habitat and exhibit multifunctional plant growth‐promoting attributes. A number of applications of PGPR formulation are needed to maintain the resistance levels in crop plants. Several microarray‐based studies have been done to identify the genes, which are associated with PGPR‐induced systemic resistance. Identification of these genes associated with ISR‐mediating disease suppression and biochemical changes in the crop plant is one of the essential steps in understanding the disease resistance mechanisms in crops. Therefore, in this review, we discuss the PGPR‐mediated innovative methods, focusing on the mode of action of compounds authorized that may be significant in the development contributing to enhance plant growth, disease resistance, and serve as an efficient bioinoculants for sustainable agriculture. The review also highlights current research progress in this field with a special emphasis on challenges, limitations, and their environmental and economic advantages.
... Antibiosis is the production and release of compounds that kill or inhibit the growth of the target pathogen; it is the best-known mechanism by which microbes can control plant diseases (Raaijmakers and Mazzola 2012). The antibiotics generally produced by diverse antagonistic bacteria consist of ammonia, butyrolactones, 2,4-diacetyl phloroglucinol (DAPG)2,4-Diacetyl phloroglucinol (DAPG), kanosamine, oligomycin A, oomycin A, phenazine-1-carboxylic acid, pyoluteorin, pyrrolnitrin, viscosinamide, xanthobaccin, and zwittermycin A (Kim et al. 1999;Raaijmakers et al. 2002;Raaijmakers and Mazzola 2012). Many of these antibiotics have a broad-spectrum activity; DAPG was reported to be the most effective and is the most extensively studied antibiotic (Raaijmakers and Mazzola 2012). ...
... It can bind to a common drug-binding site in the ATP synthase shared with other drugs 60 . Oligomycin A was obtained from culture broth of Streptomyces libani As1 isolated from sea-mud soils in Korea 59 . It showed strong antifungal activity across a range of 1xMIC (3-5µg/ml) against the hyphal growth of many phytopathogenic fungi including Magnaporthe grisea. ...
Marine-derived actinobacteria are considered as potential sources of bioactive metabolites including
antifungal substances. Fifteen out of 155 marine-derived actinobacteria exhibited strong antifungal
activity against the rice blast fungus Pyricularia oryzae. Their extracts were further determined
for minimum inhibitory concentrations (MIC) and minimum fungicidal concentrations (MFC). Ethyl
acetate extract from the strain AMA49 and its subfraction AMA49F1 strongly inhibited hyphal growth
of various P. oryzae strains with MICs (8 to 16µg/ml) and MFCs (16 to 128µg/ml) comparable to
propiconazole. Both extracts destroyed fungal membrane and organelles, completely inhibited conidial
germination, appressorium formation, and were non-toxic to Galleria mellonella. High performance
liquid chromatography/mass spectrometry identified oligomycin A and its derivatives as the active
components of AMA49F1 besides several diketopiperazines. AMA49 was identified as a Streptomyces
sp. based on morphological characteristics and 16S rDNA sequence analysis. The results suggest that
the Streptomyces sp. strain AMA49 is a potential biocontrol agent against rice blast pathogen P. oryzae.
This is the first report on the inhibitory effect of the marine-derived Streptomyces extract containing
oligomycin A and its derivatives on mycelial growth, conidial germination and appressorium formation
of P. oryzae.
... Botryt. cinerea Kim et al. (1999) Phenazine-1-caboxylate Psd. fluorescens ...
... Several metabolites with antibiotic nature produced by pseudomonads have been studied and characterized so far, e.g.,: the cyclic lipopeptide amphysin, 2,4-diacetylphloroglucinol (DAPG), oomycin A, the aromatic polyketide pyoluteorin, pyrrolnitrin, the antibacterial compound tropolone [109,110]. Other bacterial genera, such as Bacillus, Streptomyces, Stenotrophomonas spp., produce the macrolide oligomycin A, kanosamine, the linear aminopolyol zwittermicin A, and xanthobactin [111,112]. They also synthesize several enzymes that are able to disrupt fungal cell walls [39]. ...
There has been many recent studies on the use of microbial antagonists to control diseases incited by soilborne and airborne plant pathogenic bacteria and fungi, in an attempt to replace existing methods of chemical control and avoid extensive use of fungicides, which often lead to resistance in plant pathogens. In agriculture, plant growth-promoting and biocontrol microorganisms have emerged as safe alternatives to chemical pesticides.Streptomycesspp. and their metabolites may have great potential as excellent agents for controlling various fungal and bacterial phytopathogens. Streptomycetes belong to the rhizosoil microbial communities and are efficient colonizers of plant tissues, from roots to the aerial parts. They are active producers of antibiotics and volatile organic compounds, both in soil andin planta, and this feature is helpful for identifying active antagonists of plant pathogens and can be used in several cropping systems as biocontrol agents. Additionally, their ability to promote plant growth has been demonstrated in a number of crops, thus inspiring the wide application of streptomycetes as biofertilizers to increase plant productivity. The present review highlightsStreptomycesspp.-mediated functional traits, such as enhancement of plant growth and biocontrol of phytopathogens.
... Antibiosis is the production and release of compounds that kill or inhibit the growth of the target pathogen; it is the best-known mechanism by which microbes can control plant diseases (Raaijmakers and Mazzola 2012). The antibiotics generally produced by diverse antagonistic bacteria consist of ammonia, butyrolactones, 2,4-diacetyl phloroglucinol (DAPG)2,4-Diacetyl phloroglucinol (DAPG), kanosamine, oligomycin A, oomycin A, phenazine-1-carboxylic acid, pyoluteorin, pyrrolnitrin, viscosinamide, xanthobaccin, and zwittermycin A (Kim et al. 1999;Raaijmakers et al. 2002;Raaijmakers and Mazzola 2012). Many of these antibiotics have a broad-spectrum activity; DAPG was reported to be the most effective and is the most extensively studied antibiotic (Raaijmakers and Mazzola 2012). ...
... Botrytis cinerea Kim et al. (1999) ...
... Several metabolites with antibiotic nature produced by pseudomonads have been studied and characterized so far, e.g., the cyclic lipopeptide amphysin, 2,4-diacetylphloroglucinol (DAPG), oomycin A, the aromatic polyketide pyoluteorin, pyrrolnitrin, the antibacterial compound tropolone [113,114]. Other bacterial genera, such as Bacillus, Streptomyces, Stenotrophomonas spp., produce the macrolide oligomycin A, kanosamine, the linear aminopolyol zwittermicin A, and xanthobactin [115,116]. They also synthesize several enzymes that are able to disrupt fungal cell walls [39]. ...
Background: There is a growing interest in utilizing endophytes as biofertilizers or biological controls. Beneficial effects may be obtained by synthesizing phytohormones, enzymes and antagonistic substances, fixing nitrogen and carbon dioxide, inducing defence mechanisms and competing colonizing sites and nutrients. Endophytes enhance plant growth and health through plant growth promoting rhizobacteria. Endophytes enter plant tissues through root zone or aerial portions, via germinating radicles, secondary
roots, stomata, or foliar route. Endophyte-plant-polymer degrading enzymes such as cellulases and pectinases play a role for their internal colonization and can be detected by immunological or in situ
hybridization or tagging with reporter genes. Endophytes interact biochemically and genetically with their host plant and synthesize osmolytes, osmoprotectants, antioxidants, allowing the plants to mitigate the impacts of abiotic stress. Plant genes are modulated by endophyte, and the genes so expressed provide clues as to the effects of endophytes in plants.
... A large variety of antibiotics have been identified and formulated such as amphisin, 2,4-diacetylphloroglucinol (DAPG), oomycin A, phenazine, pyrrolnitrin, pyoluteorin, tensin, tropolone, hydrogen cyanide, and cyclic lipopeptides produced by Pseudomonas spp., and kanosamine oligomycin A, zwittermicin A, and xanthobaccin produced by Bacillus, Streptomyces, and Stenotrophomonas spp. [13]. Some antibiotics produced by PGPR are finding new pharmaceutical uses and these rhizobacteria opened an untapped and continuous resource for compounds to deal with the alarming arouse of multidrug-resistant pathogenic bacteria in human. ...
... A numbers of antibiotic compounds used as biocontrol mechanism of PGPR have been identified such as 2,4-diacetylphloroglucinol (DAPG), amphisin, hydrogen cyanide, oomycin A, phenazine, pyoluteorin, pyrrolnitrin, tensin, tropolone, and cyclic lipopeptides produced by pseudomonads [98][99][100] and zwittermicin A, oligomycin A, kanosamine, and xanthobaccin produced by Bacillus, Streptomyces, and Stenotrophomonas spp. [101][102][103][104]. ...
Plant growth promoting rhizobacteria (PGPR) are a group of soil microorganisms which can enhance plant growth parameters and can be used as biofertilizers. The aim of this chapter is to emphasize on the importance and use of microbial inoculants possessing P-solubilizing activities as an environment-friendly alternative to chemical phosphorus (P) fertilizers in agricultural soils. The reckless and unbalanced use of chemical fertilizers and pesticides in agricultural soil has resulted not only in the deterioration of soil health but also created some major environmental and health related issues such as soil and water pollution. Phosphorus is an essential macronutrient required for every aspect of cell biology from energy metabolism to the structure of the genetic material, and its deficiency is a severe constraint to crop production. Soil microorganisms that solubilize the least mobile P play very important role in soil biology, plant health and subsequent enhancement of crop yield. To avoid the phosphorus deficiency, phosphate solubilizing bacteria (PSB) play an important role in supplying phosphate to plants in a more environment-friendly and sustainable manner. Therefore, PSB can be used in an ideal cropping system with a lesser impact on the environment through decreased application of chemical fertilizers.
... [32] A variety of antibiotics have been identified, including compounds such as amphisin, 2,4diacetylphloroglucinol (DAPG), hydrogen cyanide, oomycin A, phenazine, pyoluteorin, pyrrolnitrin, tensin, tropolone, and cyclic lipopeptides produced by pseudomonads [37,38,39] and oligomycin A, kanosamine, zwittermicin A, and xanthobaccin. [40,41] Interestingly, some antibiotics produced by PGPB are finding new uses as experimental pharmaceuticals, [42,43] and this group of bacteria may offer an untapped resource for compounds to deal with the alarming ascent of multidrug-resistant human pathogenic bacteria. ...
Use of plant growth promoting rhizobacteria (PGPR) for the benefits of agriculture is gaining worldwide importance and acceptance and appears to be the trend for the future. Colonization of root system by PGPR implicates the production of phytohormones and other signals that lead, mostly, to enhanced lateral root branching and development of root hairs. PGPR also modify root functioning, improve plant nutrition and influence the physiology of the whole plant. Several substances produced by antagonistic rhizobacteria have been related to pathogen control and indirect promotion of growth in many plants, such as Siderophores and antibiotics. Induced systemic resistance (ISR) in plants resembles pathogen-induced systemic acquired resistance (SAR) under conditions where the inducing bacteria and the challenging pathogen remain spatially separated. Recent studies provided first clues as to how PGPR signals could trigger these plant responses. In this paper, we address novel knowledge on PGPR modes of action and signals, and highlight recent progress on potentials of PGPR in reference to biological control and signal transduction mechanism.
... In addition to metal chelaters and enzymes numerous antifungal metabolites are produced by bacteria that act against nematodes both in vitro and in vivo. These include bacillomycin [Peypoux et al., 1980, Chevanet et al., 1985, iturin [Delcambe et al., 1975; Peypoux et al., 1978; Phister et al. 2004; Mahadtanapuk et al., 2007], surfactin, mycosubtilin [Peypoux et al., 1986], bacilysin [Roger et al., 1965; Loeffler et al., 1986; Phister et al. 2004] fengymycin [Roger et al., 1965; Loeffler et al., 1986], mycobacillin [Majumdar and Bose, 1970; Mannanov and Sattarova, 2001], ammonia, butyrolactones, 2,4-diacetylphloroglucinol, HCN, kanosamine, oligomycin A, oomycin A, phenazine-1-carboxylic acid, pyoluterin, pyrrolnitrin, viscosinamide, xanthobaccin and zwittermycin A etc. [Milner et al., 1996; Keel and Defago, 1997; Whipps, 1997a; Nielson et al., 1998; Kang et al., 1998; Kim et al., 1999; Thrane et al., 1999; Nakayama et al., 1999]. ...
... Described metabolites with antibiotic activity from biocontrol strains include compounds such as amphisin, cyclic lipopeptides, 2,4-diacetylphloroglucinol, hydrogen cyanide, oomycin A, phenazine, pyoluteorin, pyrrolnitrin, tensin, and tropolone produced by pseudomonads (Défago, 1993;de Souza et al., 2003;Nielsen and Sørensen, 2003;Raaijmakers et al., 2002) and lipopeptides, kanosamine, oligomycin A, xanthobactin, and zwittermicin A produced by Bacillus, Streptomyces, and Stenotrophomonas spp. Kim et al., 1999;Milner et al., 1996;Nakayama et al., 1999;Ongena and Jacques, 2008). Agrocin 84 can be also secreted by Agrobacterium radiobacter strains (Kerr, 1980), 2,3-de-epoxy-2,3-didehydro-rhizoxin by Pseudomonas borealis MA342 (Hokeberg et al., 1998). ...
Survival of every organism on earth depends on its interactions with other organisms. For example, animals form associations with the intestinal microflora, while plants develop symbiotic associations with neighboring plants, microflora, and microfauna. Most of the associations between plants and microorganisms are mediated by organic compounds released by the plant. The plant root system acts as a factory and exudes enormous amount of chemicals to effectively communicate with the surrounding soil organisms. Bacteria on roots and in the rhizosphere can also utilize these organic compounds as a source of nutrients and enhance their population size and metabolic activities. In return, plant-associated bacteria improve plant growth and development by different mechanisms including nitrogen fixation, provision of nutrients, and mediating resistance against pathogens. Although plant–bacterial partnerships have been found effective to enhance biomass production, their importance and relevance in agricultural systems are still underestimated. A better understanding of beneficial interactions between plant, soil, and bacteria could be exploited to improve growth and health of food and feed crops. Plant growth-promoting mechanisms of bacteria might enhance biomass production in a more sustainable manner, even on marginal land. Furthermore, plant growth-promoting and/or pollutant-degrading activities of bacteria could be exploited to improve the efficiency of phytoremediation of organic and inorganic pollutants from the soil and water or to protect the food chain by decreasing the concentrations of pollutants in food crops.
... The application of a certain strain may also have a direct effect on the existence of other strains of bacteria or vice versa (COOK 1993). Some bacteria have the capability of producing antibiotics in vitro and in vivo (WELLER and THOMASHOW 1993) that may not only be toxic to microorganism in the soil but also have a negative effect on the plant growth (KIM et al. 1999). ...
After in vitro screening of more than 100 bacterial isolates from the rhizosphere on their antagonistic effect against Phytophthora fragariae var. fragariae and P. cactorum, the two causal agents of red stele and crown rot disease of strawberry, three bacteria out of different genera Raoultella terrigena (G-584), Bacillus amyloliquefaciens (G-V1) and Pseudomonas fluorescens (2R1-7) were found with the highest inhibitory effect on the mycelial growth of both Phytophthora spp. For the management of both fungal diseases the antagonistic bacteria were further evaluated under greenhouse and field conditions. In greenhouse all three bacteria were significantly effective in reducing red core and crown rot, exhibited a similar level of control as the chemical fungicide Aliette of up to 59%. In field trials conducted at different locations in Germany under artificially and naturally infested soil conditions in two season 2003 to 2005, different level of biocontrol was performed by the tested bacteria. In trial of the first season under artificial conditions, the three rizhobacteria showed a significant control up to 45% against both diseases and in the next season, only B. amyloliquefaciens was effective against red stele. Under natural conditions, significant effect of 37.5% was observed from a mixture of R. terrigena and B. amyloliquefaciens in first season and in second season R. terrigena showed significant effect of 45.1% in the northern part of Germany. In the south, R. terrigena and B. amyloliquefaciens were significantly efficient up to 51.5% and the overall effect were similar to Aliette.
... are known to show strong antibiosis to pathogens . They produce antibiotics such as butyrolactones, HCN, kanosamine, viscosinamide and zwittermycin A and many other antibiotics some of which are yet to be characterized (Kim et al. 1999; Whipps 2001). Another mechanism of biological control is the competition for nutrients. ...
Isolates of Pseudomonas species obtained from rhizosphere, rhizoplane and endophytic habitats of various plants were tested for their antagonistic activity against plant pathogenic Fusarium oxysporum isolated from the roots of a diseased pea plant. Pseudomonas isolate P5 showed best activity against F. oxysporum followed by P4, P22 and P17. Some isolates of Pseudomonas, P24, P25 and P26, grew unrestrictedly and completely covered the Fusarium colony. The antagonistic effect of Pseudomonas on F. oxysporum observed in this research can be attributed to the ability of antibiotic synthesis by Pseudomonas and also the ability to counter the toxic metabolites of Fusarium oxysporum.
... There are numerous reports of the production of antifungal metabolites by bacteria in vitro that may also have activity in vivo. Metabolites include ammonia, butyrolactones, 2,4diacetylphloroglucinol (Ph1), HCN, kanosamine, oligomycin A, oomycin A, phenazine-1-carboxylic acid (PCA), pyoluterin (Plt), pyrrolnitrin (Pln), viscosinamide, xanthobaccin, and zwittermycin A (Milner et al., 1996;Keel and Défago, 1997;Whipps, 1997;Nielsen et al., 1998;Kim et al., 1999;Nakayama et al., 1999;Thrane et al., 1999). Indeed, isolation and characterization of genes or gene clusters responsible for antibiotic production have now been achieved (Kraus and Loper, 1995;Bangera and Thomashow, 1996;Hammer et al., 1997;Nowak-Thompson et al., 1999). ...
... Described metabolites with antibiotic activity from biocontrol strains include compounds such as amphisin, cyclic lipopeptides, 2,4-diacetylphloroglucinol, hydrogen cyanide, oomycin A, phenazine, pyoluteorin, pyrrolnitrin, tensin, and tropolone produced by pseudomonads (Défago, 1993;de Souza et al., 2003;Nielsen and Sørensen, 2003;Raaijmakers et al., 2002) and lipopeptides, kanosamine, oligomycin A, xanthobactin, and zwittermicin A produced by Bacillus, Streptomyces, and Stenotrophomonas spp. Kim et al., 1999;Milner et al., 1996;Nakayama et al., 1999;Ongena and Jacques, 2008). Agrocin 84 can be also secreted by Agrobacterium radiobacter strains (Kerr, 1980), 2,3-de-epoxy-2,3-didehydro-rhizoxin by Pseudomonas borealis MA342 (Hokeberg et al., 1998). ...
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Magnaporthe oryzae is one of the most destructive fungal pathogen causing blast diseases in at least 50 grass species including wheat and rice. Although there has been comprehensive study on the fungicidal control of blast diseases, the development of pathogen resistance to commercially available products makes this approach inefficient. Novel strategies such as applying bioactive natural products against the blast fungus are required to control this economically important disease sustainably. Various classes of secondary metabolites including lipopeptides, macrolides, alkaloids, terpenoids, and phenolics from microorganisms and plants strongly suppress fungal growth and can also be effective in controlling blast diseases both in vitro and in vivo. However, precise control mechanisms of a specific blast fungus pathotype by antifungal secondary metabolites are still unclear. Commercial formulations of natural bioactive products should be cheap and safe, but the availability of these antifungal compounds for practical application is limited. This book chapter discusses the infection pathway of blast fungus and reviews naturally occurring antifungal secondary metabolites potential for controlling blast disease in cereal crops. The modes of actions of some potential antifungal secondary metabolites against blast fungus are also discussed.KeywordsAntifungal secondary metabolitesBlast diseaseBio-control
Magnaporthe oryzae
Tea (Camellia sinensis (L) O. Kuntze) is a long‐duration monoculture crop prone to several biotic (fungal diseases and insect pest) and abiotic (nutrient deficiency, drought, and salinity) stress that eventually result in extensive annual crop loss. The specific climatic conditions and the perennial nature of the tea crop favor growth limiting abiotic factors, numerous plant pathogenic fungi (PPF), and insect pests. The review focuses on the susceptibility of tea crops to PPF/pests, drought, salinity, and nutrient constraints and the potential role of beneficial actinobacteria in promoting tea crop health. The review also focuses on some of the major PPF associated with tea, such as Exobasidium vexans, Pestalotiopsis theae, Colletotrichum acutatum, and pests (Helopeltis theivora). The phylum actinobacteria own a remarkable place in agriculture due to the biosynthesis of bioactive metabolites that assist plant growth by direct nutrient assimilation, phytohormone production, and by indirect aid in plant defense against PPF and pests. The chemical diversity and bioactive significance of actinobacterial metabolites (antibiotics, siderophore, volatile organic compounds, phytohormones) are valuable in the agro‐economy. This review explores the recent history of investigations in the role of actinobacteria and its secondary metabolites as a biocontrol agent and proposes a commercial application in tea cultivation.
The increasing phytopathogens have become a chronic threat to food production intimidating food security. The practice of chemical pesticides on a large-scale worldwide has although ensured massive killing of pests but has also shown alarming impact on the nontarget organisms disturbing the microbial interactions as well as affecting the soil health enormously. Bacterial endophytes inhabiting the plant tissues have emerged as a more environmentally friendly alternative. The beneficial effects of these endophytes are similar to those of the rhizosphere bacteria. It can suppress the diseases in pathosystems and can also increase phytoimmunity to resist the disease. It is also established as a prospective growth-promoting agent resulting in soil and plant health restoration. A variety of mechanisms including competition for an ecological niche, antibiosis, parasitism, induction of systemic resistance, and inhibitory allelochemicals production in the host system, are the ways of bacterial endophytes to control the infection caused by broad-spectrum phytopathogens. However, still numerous challenges remain before exploiting, as the inherent characteristics of the endophyte and the environmental conditions they are adapted to. Understanding the mechanisms of their action and its regulation through the emerging genomic technologies and interdisciplinary research approaches can be helpful in targeting potent biocontrol bacterial endophytes. This chapter focuses on the recent works on the mechanisms and the principle of actions of bacterial endophytes against the phytopathogens and emphasizes the use and commercialization of biocontrol agents for treating plant diseases.
Pseudomonas fluorescens is the habitat of soil, water and plant surface. It is a gram-negative, rod-shaped bacterium. It produces a soluble greenish fluorescent pigment called fluorescein, which secretes under low iron conditions. An eco-friendly approach to the control of plant diseases is an emerging need for agriculture in the twenty‐first century. The beneficial rhizobacteria are coming up as an alternative to chemicals at certain extent. Avenues of biological control are plant growth-promoting rhizobacteria (PGPR), which have found potential in preventing phytopathogens causing diseases in plants. The best-characterized biocontrol PGPR belongs to the bacteria genus Pseudomonas. Fluorescent pseudomonads are most suitable in the application of biological control because of their abundant population in soils and plant root system and their capability to utilize many plant exudates as a nutrient. They can adhere to soil particles and also in rhizoplane, motility, synthesis of antibiotics, and production of hydrolytic enzymes. In addition, it also possesses plant growth-promoting traits such as nitrogen fixation, phosphate solubilization, iron chelation, and phytohormone production. The varied utility of P. fluorescens places them at the top most choice to be exploited as a growth promoter and disease suppressor in the field of agriculture. They are producing the substances viz. antibiotics, siderophores, and a spread of enzymes or by induction of systemic resistance in host plants. These microorganisms also can function as competitors of pathogens for nutrition. Antibiotics is one of the important mechanisms used by the biocontrol agent are identified as pyrrolnitrin, pyoluteorin, phenazine, amphisin, 2,4, diacetylphloroglucinol (DAPG), oomycin A, tensin, tropolone, compound and cyclic lipopeptides. The addition of antagonistic antimicrobial producing bacterial strains, either individually or as a mixture in combination with fungicide, significantly decreased the plant disease stress. The present chapter refers to the occurrence, distribution, mechanism of biocontrol against many diseases of agriculture and horticultural crops.
Botrytis cinerea is one of the most destructive fungal pathogens which can cause gray mold diseases of numerous plant species, while the frequent applications of fungicides also result in the fungicide-resistances of B. cinerea. In this study, a new Streptomyces strain FX13 was obtained to show biocontrol potentials against fungicide-resistant B. cinerea B3–4. Its in vitro and in vivo antifungal mechanisms were further investigated. The results showed that the culture extract of strain FX13 could significantly inhibit the mycelia growth of B. cinerea B3–4 with the EC50 value of 5.40 mg L⁻¹, which was greatly lower than those of pyrisoxazole, boscalid and azoxystrobin. Further bioassay-guided isolation of the extract had yielded the antifungal component SA1, which was elucidated as a 26-membered polyene macrolide of oligomycin A. SA1 could inhibit the mycelia growth, spore germination, germ tube elongation and sporogenesis of B. cinerea B3–4 in vitro, and also showed significant curative and protective effects against gray mold on grapes in vivo. Moreover, SA1 could result in the loss of membrane integrity and the leakage of cytoplasmic contents, which might be related to the accumulation of reactive oxygen species (ROS) and membrane lipid peroxidation. Besides, intracellular adenosine triphosphatase (ATPase) activity and adenosine triphosphate (ATP) content of B. cinerea B3–4 decreased after SA1-treatment. Overall, the oligomycin A-producing strain FX13 could inhibit fungicide-resistant B. cinerea B3–4 in vitro and in vivo, also highlighting its biocontrol potential against gray mold.
The term “endophyte” was first introduced by De Bay in 1886 to explore the symbiotic microbiota to contain the plant diseases like probiotic microbiota in human being. The modern intensive farming system enhanced the use of chemical synthetic pesticides to increase the crop production in agri-horti ecosystems for many decades. Due to the hazardous effect of pesticides on soil health, human health, and the environment, this is likely to be limited in future. As an alternative strategy, the secondary metabolites produced by agriculturally important microorganisms are explored, which are residing in the host plants as epiphytes and endophytes and play an important role in improving the quality of the crops. Microorganisms synthesize enzymes, compounds either alone or in association with the host plants, which are eco-friendly, toxic to plant pathogens, and do not harm human beings and other living organisms. Inoculation with endophytes modulates the synthesis of bioactive compounds with high pharmaceutical properties in addition to plant growth promotion. In this review, we have focused on the need for exploration of alternative microbial habitats for isolating novel microbes with chemical and functional diversity.
Oligomycins are macrolide antibiotics, produced by Streptomyces spp. that show antagonistic effects against several microorganisms such as bacteria, fungi, nematodes and the oomycete Plasmopara viticola. Conidiogenesis, germination of conidia and formation of appressoria are determining factors pertaining to pathogenicity and successful diseases cycles of filamentous fungal phytopathogens. The goal of this research was to evaluate the in vitro suppressive effects of two oligomycins, oligomycin B and F along with a commercial fungicide Nativo® 75WG on hyphal growth, conidiogenesis, conidial germination, and appressorial formation of the wheat blast fungus, Magnaporthe oryzae Triticum (MoT) pathotype. We also determined the efficacy of these two oligomycins and the fungicide product in vivo in suppressing wheat blast with a detached leaf assay. Both oligomycins suppressed the growth of MoT mycelium in a dose dependent manner. Between the two natural products, oligomycin F provided higher inhibition of MoT hyphal growth compared to oligo-mycin B with a minimum inhibitory concentration of 0.005 and 0.05 μg/disk, respectively. The application of the compounds completely halted conidial formation of the MoT mycelium in agar medium. Further bioassays showed that these compounds significantly inhibited MoT conidia germination and induced lysis. The compounds also caused abnormal germ tube formation and suppressed appressorial formation of germinated spores. Interestingly, the application of these macrolides significantly inhibited wheat blast on detached leaves of wheat. This is the first report on the inhibition of mycelial growth, conidiogenesis, germination of conidia, deleterious morphological changes in germinated conidia, and suppression of blast disease of wheat by oligomycins from Streptomyces spp. Further study is needed to unravel the precise mode of action of these natural compounds and consider them as bio-pesticides for controlling wheat blast.
Higher plants continually compete with microbes to conserve their predominance within the particular niche. Plants have evolved constant relationships with a suite of microbes, known as the phytomicrobiome. The associates of phytomicrobiome exhibit symbiotic relationship. Plant-microbe and microbe-microbe interactions within the phytomicrobiome are carried out through the release of signalling compounds. Bacterial community within the phytomicrobiome communicates among themselves through quorum-sensing mechanism. Diversity, stability and resilience of microbial community in phytomicrobiome are the major determinants of plant health and productivity. Therefore, phytomicrobiome is under intensive investigation to improve our understanding of its strong effects on plant development, health and resistance to parasites. Exploration of the plant-microbe interactions within the phytomicrobiome is a promising avenue to improve crop productivity and agricultural sustainability. Understanding the regulation and relatedness of plant and microbial community may aid in engineering plants with improved pathogen resistance and novel symbiotic interactions. Comprehensive study of phytomicrobiome, especially the molecular signalling pathway, may provide new insights into the mechanism of plant disease management, successively inspiring new plant breeding strategies.
Citrus canker is a devastating disease of citrus caused by Xanthomonas citri subsp. citri (Xcc). A total of 134 endophytic bacteria were isolated from various gymnospermic and angiospermic plants. They were screened for their antagonistic activities against three wild-type and six streptomycin-resistant Xcc strains. TbL-22 and TbL-26, both later identified as Bacillus thuringiensis, inhibited all the wild and resistant Xcc strains. TbL-22 exerted the highest antagonistic activity against XccW3 and XccM6 with inhibition zones of 20.64 ± 0.69 and 19.91 ± 0.87 mm, respectively. Similarly ethyl acetate extract of TbL-22 showed highest inhibition zones 15.31 ± 2.08 and 19.37 ± 3.17 mm against XccW3 and XccM6, respectively. TbL-22 reduced canker incidence on infected leaves by 64.05% relative to positive controls. Scanning electron microscopy revealed that the cell membranes of Xcc treated with ethyl acetate extract of TbL-22 were ruptured, lysed, and swollen. B. thuringiensis TbL-22 can effectively and sustainably controls streptomycin-resistant citrus canker.
Crop plants play an outstanding function in providing food and energy to humans. Rice (Oryza sativa L.) is one of the most important stable crops that have a role in providing the main food to more than half of the world’s people. One of the important factors in increasing yield in rice is the balanced nutrition or supply of the required nutrients in the proper form and ratios. Chemical fertilizers are essential components of modern agriculture by providing essential plant nutrients. However, the overuse of these fertilizers causes serious environmental pollution. But threats of plant pathogens on the attack and damages on the crop productivity cannot be ruled out. Therefore, chemical-based pesticides are thought to be an effective and trustworthy agricultural management measure for repressing pests. Nowadays, the use of beneficial microorganisms and biological control agents are proved as good as synthetic pure/chemicals for the increased plant growth and yield. The diminished utilization of chemical fertilizers for the management of plant pathogens is considered as a secure and maintainable strategy for safe and rewarding agricultural productivity. Based on research conducted until this moment, rice-associated bacteria are encouraging alternatives to chemical fertilizers in an eco-friendly manner. In general, the application of plant growth-promoting bacteria (PGPB) could offer a cheaper and cost-effective approach to overcome the environmental problems caused by chemical fertilizers and their use in the form of biofertilizers and biopesticides could decrease our reliance on synthetic agrochemicals. This chapter highlights the importance of PGPB for enhancing sustainable rice production.
The emergence of drug resistance in infectious microbial strains can be overcome by development of novel drug molecules against unexploited microbial target. The success of Bedaquiline in recent years, as FoF1 ATP synthase inhibitor against XDR and MDR mycobacterium strains, has resulted in further exploration to identify more potent and safe drug molecules against resistant strains. FoF1 ATP synthase is the main energy production enzyme in almost all eukaryotes and prokaryotes. Development of bacterial ATP synthase inhibitors is a safe approach, without causing harm to mammalian cells due to structural difference between bacterial and mammalian ATP synthase target sites. This review emphasizes on providing the structural insights for FoF1 ATP synthase of different prokaryotes and will help in the design of new potent antimicrobial agents with better efficacy. Further, applications of synthetic and natural active antimicrobial ATP synthase inhibitors, reported by different research groups are summarized. Their SAR and mode of actions are also analysed.
The present work was undertaken with an objective to study the effect of culture filtrates and secondary metabolites of three Streptomyces spp. from black pepper rhizosphere having promising biocontrol and growth promoting traits on different developmental stages of pathogens like Phytophthora capsici and Sclerotium rolfsii. The study also focuses on identification of compounds responsible for the antimicrobial and growth promotive activity. Crude culture filtrate of IISRBPAct1 and IISRBPAct25 were found inhibitory to mycelial growth of P. capsici. Diluted culture filtrate of IISRBPAct1 (2 %) and IISRBPAct25 (5 %) were found inhibitory to the sporangia formation. Crude culture filtrate of IISRBPAct1 can completely inhibit the zoospore germination while it was inhibited to 98.6 % and 87 % by 10 % diluted extracts of IISRBPAct1 and IISRBPAct25 respectively. IISRBPAct1 showed 51.27 % inhibition of mycelial growth of S. rolfsii, while IISRBPAct25 and IISRBPAct42 showed 57.63 % and 26.90 % inhibition respectively. IISRBPAct1 is highly inhibitory to sclerotial formation even at 1 % concentration. The secondary metabolites of the three isolates were extracted in three solvent systems and their activity profile was detected and characterized by HPTLC. High resolution UPLC- (ESI)-QToF-MS analysis of the extracts revealed the presence of a vast array of antifungal compounds that supports the antimicrobial activity of culture filtrate and metabolites of the isolates.
The quest for increasing agricultural production for the burgeoning human population had been effective with the use of nitrogen-based fertilizers. However, its prolong use and occurrence of acid rain resulted in dropping the soil pH below 5.0, whose environmental conditions considerably decreased the beneficial effects of soil neutrophilic bacteria while increasing the abundance of pathogenic fungi. Furthermore, the use of pesticide and synthetic fertilizers had adverse effect on human health and environment. An alternative method will therefore rely on minor groups of bacteria that can sustain its growth under extreme condition. And particularly for designing products to be applied in acidic soil, acidophilic and/or acidotolerant Actinobacteria having antifungal and/or plant growth-promoting activities had tremendous potential for developments as novel biocontrol and/or biofertilizer products. As Actinobacteria can survive under many adverse environment conditions by forming spores, they can be promising bio-agents for sustainable agricultural production. Actinobacteria may help in the degradation of organic matter into humus and release of nitrogen, carbon, and ammonia, in turn supplying the nutrients to agricultural crops in acidic soil. Release of ammonia due to decomposition of chitin by chitinase-producing Actinobacteria may raise the pH of soils, paving a way for other neutrophilic plant growth-promoting bacteria.
Plant Growth Promoting Rhizobacteria (PGPR) represent an alternative to improve plant growth and yield as well as to act as agents of biocontrol. This study characterized isolates of Streptomyces spp. (Stm) as PGPR, determined the antagonism of these isolates against Pectobacterium carotovorum subsp. brasiliensis (Pcb), evaluated the ability of Stm on promoting growth and modulating the defense-related metabolism of tomato plants, and the potential of Stm isolates on reducing soft rot disease in this species. The VOC profile of Stm was also verified. Promotion of plant growth was assessed indirectly through VOC emission and by direct interaction with Stm isolates in the roots. Evaluation of soft rot disease was performed in vitro on plants treated with Stm and challenged with Pcb. Enzymes related to plant defense were then analyzed in plants treated with three selected isolates of Stm, and PM1 was chosen for further Pcb-challenging experiment. Streptomyces spp. isolates displayed characteristics of PGPR. PM3 was the isolate with efficient antagonism against Pcb by dual-culture. Most of the isolates promoted growth of root and shoot of tomato plants by VOC, and PM5 was the isolate that most promoted growth by direct interaction with Stm. Soft rot disease and mortality of plants were significantly reduced when plants were treated with StmPM1. Modulation of secondary metabolism was observed with Stm treatment, and fast response of polyphenoloxidases was detected in plants pretreated with StmPM1 and challenged with Pcb. Peroxidase was significantly activated three days after infection with Pcb in plants pretreated with StmPM1. Results suggest that Streptomyces sp. PM1 and PM5 have the potential to act as PGPR.
The rhizosphere of plant species is an inimitable ecosystem that harbors an extensive range of microbes. Research in the wide areas of rhizosphere biotechnology highlighting new bioinoculants has received ample attention during recent past, and suitable expertises have been developed. However, the global recognition of such technologies by farmers is still overwhelmed with doubts owing to limited shelf-life and efficiency of the products which demonstrate discrepancies. This review illustrates plant growth-promoting rhizobacteria with detailed emphasis on nutrient acquisition and potential roles in conferring tolerance against abiotic stresses. The review demonstrates the recent research in the field of genomic and proteomic analysis, where systematic characterization of potentially effective rhizobacteria is being carried out by screening the extensive bacterial gene pool based on modern molecular tools. The review concludes by emphasizing the efforts made in the proteomics field which could compensate for understanding of prompt evolution in microbe-derived and plant-derived protein and metabolite substitute that activates vulnerability or resistance.
The use of microorganisms for biocontrol agents has become an effective alternative technology. Bacteria from marine environment are an underutilized source of novel antibiotics. The bacterial strain CMG1055 which showed strong antifungal activity against pathogenic fungi was isolated from surface water of Arabian Sea of Pakistan. Based on the physiological and biochemical characteristics and 16S ribosomal RNA sequence analysis, the bacterial strain CMG1055 was identified as Pseudomonas aeruginosa. This bacterium exhibited varying degrees of antifungal activities against a number of pathogenic fungi, such as A. niger, Helimanthosporium sp, T. mentagrophytes, C. albicans, S. cerevisiae, and Rhizpopus sp. The production of antifungal activity showed a great degree of media specificity and it was strictly restricted to King B agar supplemented with 20 % glycerol. No production of antifungal activity was detected in Tris glucose minimal medium. Antifungal compound(s) produced by CMG1055 was extracted using 80% acetone and ethyl acetate from the growth medium and purified by silica gel column chromatography. The minimal inhibitory concentration ranged from 50 to 75 μg/mL. Chemically the antifungal substance was a phenolic compound with aromatic unsaturation, as confirmed by UV and IR spectroscopy.
Root colonizing bacteria (rhizobacteria) that exert beneficial effects on plant development via direct or indirect mechanisms have been defined as plant growth promoting rhizobacteria (PGPR). The search for PGPR and investigation of their modes of action are increasing at a rapid pace as efforts are made to exploit them commercially as biofertilizers. This review focuses on different kinds of PGPR, their mode of action as biofertilizers and also development of microbial consortia is mentioned. These mode of action include fixing N2, increasing the availability of nutrients in the rhizosphere, positively influencing root growth and morphology. Although significant control of plant pathogens or direct enhancement of plant development has been demonstrated by PGPR in the laboratory and in the greenhouse, results in the field have been less consistent. Because of these and other challenges in screening, formulation, and application, PGPR have yet to fulfill their promise and potential as commercial inoculants. Recent progress in our understanding of their diversity, colonization ability, mechanism of action, formulation, and application should facilitate their development as reliable components in the management of sustainable agricultural systems. Obtaining maximum benefits on farms from plant growth promoting biofertilizers will require a systematic strategy designed to fully utilize all these beneficial factors, allowing crop yields to be maintained or even increased with reduced fertilizer applications.
We reviewed the respective biocontrol contributions of fluorescent pseudomonads and other plant-protecting microorganisms in disease-suppressive soils. The ability to inhibit soil-borne pathogens and to protect plants occurs both in Pseudomonas and non-Pseudomonas microorganisms, including diverse bacteria and fungi, and both play important roles in soil suppressiveness. In Pseudomonas, antibiosis and competition were shown to be important mechanisms of pathogen suppression, though direct effects on plant, e.g. induced systemic resistance, phytohormone interference and plant-growth promotion, were also reported. These types of mechanisms occur also in non-Pseudomonas biocontrol microbes, some of them also displaying hyperparasitism in certain types of suppressive soils. This review shows that in suppressive soils where Pseudomonas play an important role, the roles of non-Pseudomonas microorganisms were often neglected, and vice versa. Yet, Pseudomonas and other microorganisms may interact with each other in the rhizosphere and with the plant, and some recent studies indicate that disease suppressiveness is an emerging soil property that can typically result from these multiple interactions. In conclusion, we propose that a parallel assessment of Pseudomonas and non-Pseudomonas microorganisms in suppressive soils, e.g. using microarrays or metagenomics, may bring a better understanding of disease suppressiveness.
Plant growth promoting rhizobacteria (PGPR) colonizes the root system of plants and can modulate plant growth by enhancing the availability of nutrients and protect the plant from phytopathogens. For a long period, PGPR were mainly used as biofertilizers in agriculture fields. Biological control of plant diseases has emerged as a promising alternative to synthetic pesticides and fungicides. Recently, the application of PGPR has been extended to control several diseases in economically important plants. Numerous unequivocal evidences suggest that PGPR play a key role in the suppression of various plant pathogens by different mechanisms. This review presents the recent advances in our understanding of biological control by PGPR and their interactions with the plant system.
Soil microorganisms are known to play an active role in increased crop yields and soil fertility through a diverse array of mechanisms and such organisms are termed as PGPR (Plant Growth Promoting Rhizobacteria). This enhancement has been attributed to their involvement in the cycle of nutrients like carbon and nitrogen or in the decomposition of the organic matter, or production of allelopathic metabolites or enzymes influencing the pathogenic flora/fauna which indirectly promotes plant growth. Cyanobacteria are a ubiquitous group of organisms which have been relatively less investigated as PGPR, although their role in nitrogen dynamics of paddy based cropping systems is well investigated. Cyanobacteria are known to produce compounds with a wide range of activities, including phytohormones, biocidal metabolites or nutraceuticals. The interactions between agriculturally useful heterotrophic bacteria and autotrophs such as cyanobacteria can be effective and environment friendly options as biocontrol agents and biofertilizers. Plant-microbe partnerships are increasingly being focussed for not only nutrient management, but also for improving biomass production and remediation of polluted/inhospitable environments. This compilation provides an overview of the developments on this aspect and projections for the future.
Microbial metabolites attract increasing attention as potential pesticides. They are expected to overcome the resistance and pollution that have accompanied the use of synthetic pesticides. Several microbial metabolites, such as avermectin, have proved useful as agroactive agents. In this review, we attempt to identify newer agroactive microbial metabolites with feasible activity or interesting action sites from those reported in recent years. In addition, microbial and chemical modifications of existing microbial agrochemicals are discussed to illustrate the usefulness of these technologies in potentiating agroactivity and stability. We discuss the possibility of future discovery of excellent microbial agrochemicals, and the importance of efforts to promote positive public perception and public acceptance of pesticide chemicals.
The (,,)-configuration (1) of the strobilurins has been confirmed by stereocontrolled synthesis.
Efficient, stereocontrolled syntheses of the antifungal metabolites oudemansin A and B are described.
The strategy and synthetic efforts leading to efficient stereoselective syntheses of thiangazole, a tris-thiazolinyl-oxazole metabolite isolated from Polyangium spp., and of hydantocidin, a spironucleoside metabolite isolated from Streptomyces hygroscopicus, are discussed.
Holocarboxylase synthetase (HCS) plays an essential role in biotin utilization in eukaryotic cells and its deficiency causes biotin-responsive multiple carboxylase deficiency in humans. We have cloned the human HCS cDNA and show that antiserum against the recombinant protein immunoprecipitates human HCS. A one base deletion resulting in a premature termination and a missense mutation (Leu to Pro) were found in cells from siblings with HCS deficiency. Human HCS shows homology to BirA, which acts as both a biotin-[acetyl-CoA-carboxylase] ligase and a biotin represser in E. coli, suggesting a functional relationship between the two proteins. The human HCS gene maps to chromosome 21q22.1.
The structures of oligomycins A (2) and C (3) were established by chemical correlation of their respective degradation products with those derived from oligomycin B, whose structure is known. The mass spectral fragmentation behavior of the spiroketal under electron impact conditions is discussed.
A manumycin-type antibiotic, SW-B, has been isolated from the solid agar culture of Streptomyces flaveus strain A-11. The structure was determined by mass spectrometry and one- and two-dimensional NMR spectroscopy. SW-B was detected at Rf 0.5 on the TLC plate developed with chloroform−methanol (90:10 v/v). The UV spectrum of SW-B in methanol showed peaks at 208 and 260 nm. The antibiotic SW-B was confirmed to be a derivative of a manumycin-type antibiotic, 2,4,6-trimethyldeca-(2E,4E)-dienamide (C13H23NO, 209.1780). SW-B showed strong antifungal activity against Phytophthora capsici, Magnaporthe grisea, Cladosporium cucumerinum, and Alternaria mali. However, it lacked antimicrobial activity against yeast and bacteria. Keywords: 2,4,6-Trimethyldeca-(2E,4E)-dienamide; manumycin; Streptomyces flaveus; antifungal activity
Gopalamicin, an antifungal antibiotic, was isolated from the cells of two actinomycetes, MSU-625 and MSU-616. Gopalamicin is structurally similar to salbomycin and elaiophylin. Gopalamicin completely inhibited the growth of all pathogenic fungi tested in vitro at 12-16 ppm. Similarly, it was somewhat effective in controlling wheat powdery mildew, grape downy mildew, and rice blast pathogens in greenhouse experiments. Gopalamicin was ineffective against all Gram-positive and -negative bacteria tested.
Thioulutin (Ia) and aureothricin (Ib) are shown to be acetamido and propionamido derivatives, respectively, of 3-amino-5-methylpyrrolin-4-ono-(4,3-d)-1,2-dithiole (Ic).
The antibiotic complex, oligomycin, has been separated into three biologically active components A, B and C. One crystalline preparation contained 67% A, 13% B and 20% C, another 20% A, 80% B and no C. The components were homogeneous and analyzed for the formulas: A, C24H40O6; B, C22H36O6; C, C28H46O6. The oligomycins are neutral, unsaturated, optically active alcohols, soluble in many organic solvents but very insoluble in petroleum ether and water. Comparison of the physical, chemical and biological properties indicates that, while there are differences, the three antibiotics are closely related in structure.
A total synthesis of griseofulvin has been achieved. The key step involved is a Diels-Alder cycloaddition between 1,1-dimethoxy-3-trimethylsilyloxy-1,3-butadiene (4) and 7-chloro-4,6-dimethoxy-2-(1-phenylsulfinylethylidene)-3(2H)-benzofuranone (20) to afford dl-5′,6′-dehydrogriseofulvin (13).
The antibiotic nucleoside tubercidin produced by Streptomyces viola-ceoniger was evaluated for in-vivo efficacy and in-vitro activity against Phytophthora capsici, Magnaporthe grisea and Colletotrichum gloeosporioides. Tubercidin was more effective against P. capsici and M. grisea than against C. gloeosporioides in inhibiting mycelial growth. The bioassay on TLC plates was the most sensitive method and allowed the evaluation of antifungal activity of tubercidin even at a low concentration of 0.1 μgml−1. As compared to the systemic fungicide metalaxyl, tubercidin was similar or somewhat higher in inhibition of mycelial growth of P. capsici. When applied to pepper stems, tubercidin was equally as effective as metalaxyl in the control of phytophthora blight in pepper plants, irrespective of application time and concentration. The treatment with 1000 μg ml−1 tubercidin induced phytotoxicity in pepper plants. No control efficacy of phytophtora blight was observed in pepper plants supplied with a soil drench of tubercidin. Treatment with tubercidin at 500 μg ml−1 completely protected pepper plants at first branch stage from phytophthora blight until four days after application. The control efficacy of tubercidin drastically declined seven days after application.
A simple bioautographic techniqud according to WELTZIEN', and modified by
DEISHUI JZEN~ for detection of fungitoxic substances has been in use for many years
in this laborattiry. Chromatograms on Whatman No. 3MM paper are develpped with
propanol-water (85: 15) and after drying are sprayed with a conidial suspension of
Glomerella cingzclata. After incubation, clearly visible inhibition zones indicate the
preserice of. fungitoxic compounds. Chromatography thus permits not only the detection
sf fungitoxic substances per se, but also makes the study of the conversion
reactions and of decomposition of such compounds possible.
Approximately 50 toxic antibiotics were tested as possible inhibitors of respiratory and phosphorylating systems in mitochondria and of glycolysis by Ascites tumor cells.Oligomycin, Nigericin, and Dianemycin inhibited respiration and phosphate uptake in the presence of several substrates. Each of these agents displayed considerable selectivity in these systems as well as in their inhibition of mitochondrial adenosinetriphosphatase (ATPase). Oligomycin inhibits, virtually completely, the ATPase and the ATP-Pi32 exchange reaction in mitochondria and in submitochondrial particles. The effects of Nigericin and Dianemycin are dependent to some extent on the structural integrity of the mitochondria.Two antibiotics which are known to affect electron-carrying systems were found to inhibit, partially, anaerobic glycolysis in Ascites tumor cells.The results affirm the general utility of toxic antibiotics as tools for metabolic investigations.
Fungicides continue to be essential for the effective control of plant diseases. New classes of fungicides with novel modes of action are being developed in the 1990s. These include the strobilurins, phenylpyrroles, anilinopyrimidines, phenoxyquinolines, and compounds that trigger defense mechanisms in the plant. For the foreseeable future, new toxophores will be identified through a process of random screening, with natural products representing a rich source of fungicide leads. Progress is being made in the development of high-throughput screens comprised of target enzyme sites or cell-based assays; these techniques will improve the probability of discovery. Following the identification of suitable leads, biorational design is used to optimize specific properties. In vivo glasshouse screens and field trials are expected to remain the dominant methods for characterizing new compounds. Low toxicity to humans and wildlife, low environmental impact, low residues in food, and compatibility with integrated pest management (IPM) programs are increasingly important considerations in the selection of fungicides for development.