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Perera M, Wijayarathna D, Wijesundera S, Chinthaka M, Seneviratne G, Jayasena S. Biofilm mediated synergistic degradation of hexadecane by a naturally formed community comprising Aspergillus flavus complex and Bacillus cereus group. BMC Microbiol 2019; 19:84. [PMID: 31035915 PMCID: PMC6489202 DOI: 10.1186/s12866-019-1460-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Accepted: 04/17/2019] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND The hydrophobic nature of hydrocarbons make them less bioavailable to microbes, generally leading to low efficiency in biodegradation. Current bioremediation strategies for hydrocarbon contamination, uses induced mixed microbial cultures. This in-vitro study demonstrates the utilization of naturally occurring communities in suitable habitats for achieving highly efficient, synergistic degradation of hydrocarbons in a simple community structure without additives. METHODS Enrichment media supplemented with 1% (7652.53 mg/L) hexadecane (HXD) as the sole carbon source were inoculated with samples of soil with waste polythene, collected from a municipal landfill in order to isolate microbial communities. Gas Chromatography-Mass Spectrometry (GC-MS) analysis was performed on HXD grown co-cultures and individual counterparts after 14 days incubation and percentage degradation was calculated. Microbes were identified using 16S rRNA gene and Internal Transcribed Spacer region sequencing. Biofilm formation was confirmed through scanning electron microscopy, in the most efficient community. RESULTS Three mixed communities (C1, C2 and C3) that demonstrated efficient visual disintegration of the HXD layer in the static liquid cultures were isolated. The C1 community showed the highest activity, degrading > 99% HXD within 14 days. C1 comprised of a single fungus and a bacterium and they were identified as a Bacillus sp. MM1 and an Apsergillus sp. MM1. The co-culture and individual counterparts of the C1 community were assayed for HXD degradation by GC-MS. Degradation by the fungal and bacterial monocultures were 52.92 ± 8.81% and 9.62 ± 0.71% respectively, compared to 99.42 ± 0.38% by the co-culture in 14 days. This proved the synergistic behavior of the community. Further, this community demonstrated the formation of a biofilm in oil-water interface in the liquid medium. This was evidenced from scanning electron microscopy (SEM) showing the Bacillus cells attached on to Aspergillus mycelia. CONCLUSIONS This study demonstrates the utilization of naturally formed fungal-bacterial communities for enhanced biodegradation of hydrocarbons such as hexadecane and reports for the first time, synergistic degradation of hexadecane through biofilm formation, by a community comprising of Bacillus cereus group and Aspergillus flavus complex.
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Affiliation(s)
- Madushika Perera
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Colombo, Colombo 08, Sri Lanka
| | | | - Sulochana Wijesundera
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Colombo, Colombo 08, Sri Lanka
| | - Manoj Chinthaka
- Department of Chemistry, Faculty of Applied Sciences, University of Sri Jayewardenepura, Nugegoda, Sri Lanka
| | - Gamini Seneviratne
- National Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka
| | - Sharmila Jayasena
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Colombo, Colombo 08, Sri Lanka.
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Cross M, Biberacher S, Park S, Rajan S, Korhonen P, Gasser RB, Kim J, Coster MJ, Hofmann A. Trehalose 6‐phosphate phosphatases of
Pseudomonas aeruginosa. FASEB J 2018; 32:5470-5482. [DOI: 10.1096/fj.201800500r] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Megan Cross
- Griffith Institute for Drug Discovery, Griffith UniversityNathan QueenslandAustralia
| | - Sonja Biberacher
- Griffith Institute for Drug Discovery, Griffith UniversityNathan QueenslandAustralia
- Department of BiologyFriedrich‐Alexander University, Erlangen‐NurembergErlangenGermany
| | - Suk‐Youl Park
- Pohang Accelerator Laboratory, Pohang University of Science and TechnologyPohang GyeongbukSouth Korea
| | - Siji Rajan
- Griffith Institute for Drug Discovery, Griffith UniversityNathan QueenslandAustralia
| | - Pasi Korhonen
- Department of Veterinary BiosciencesMelbourne Veterinary School, The University of MelbourneParkville VictoriaAustralia
| | - Robin B. Gasser
- Department of Veterinary BiosciencesMelbourne Veterinary School, The University of MelbourneParkville VictoriaAustralia
| | - Jeong‐Sun Kim
- Department of ChemistryChonnam National UniversityGwangjuSouth Korea
| | - Mark J. Coster
- Griffith Institute for Drug Discovery, Griffith UniversityNathan QueenslandAustralia
| | - Andreas Hofmann
- Griffith Institute for Drug Discovery, Griffith UniversityNathan QueenslandAustralia
- Department of Veterinary BiosciencesMelbourne Veterinary School, The University of MelbourneParkville VictoriaAustralia
- Queensland Tropical Health AllianceSmithfield QueenslandAustralia
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Velmourougane K, Prasanna R, Saxena AK. Agriculturally important microbial biofilms: Present status and future prospects. J Basic Microbiol 2017; 57:548-573. [PMID: 28407275 DOI: 10.1002/jobm.201700046] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 03/17/2017] [Accepted: 03/19/2017] [Indexed: 11/07/2022]
Abstract
Microbial biofilms are a fascinating subject, due to their significant roles in the environment, industry, and health. Advances in biochemical and molecular techniques have helped in enhancing our understanding of biofilm structure and development. In the past, research on biofilms primarily focussed on health and industrial sectors; however, lately, biofilms in agriculture are gaining attention due to their immense potential in crop production, protection, and improvement. Biofilms play an important role in colonization of surfaces - soil, roots, or shoots of plants and enable proliferation in the desired niche, besides enhancing soil fertility. Although reports are available on microbial biofilms in general; scanty information is published on biofilm formation by agriculturally important microorganisms (bacteria, fungi, bacterial-fungal) and their interactions in the ecosystem. Better understanding of agriculturally important bacterial-fungal communities and their interactions can have several implications on climate change, soil quality, plant nutrition, plant protection, bioremediation, etc. Understanding the factors and genes involved in biofilm formation will help to develop more effective strategies for sustainable and environment-friendly agriculture. The present review brings together fundamental aspects of biofilms, in relation to their formation, regulatory mechanisms, genes involved, and their application in different fields, with special emphasis on agriculturally important microbial biofilms.
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Affiliation(s)
| | - Radha Prasanna
- Division of Microbiology, ICAR-Indian Agricultural Research Institute, New Delhi, India
| | - Anil Kumar Saxena
- ICAR-National Bureau of Agriculturally Important Microorganisms (NBAIM), Mau Nath Bhanjan, Uttar Pradesh, India
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Multifunctional Exopolysaccharides from Pseudomonas aeruginosa PF23 Involved in Plant Growth Stimulation, Biocontrol and Stress Amelioration in Sunflower Under Saline Conditions. Curr Microbiol 2014; 69:484-94. [DOI: 10.1007/s00284-014-0612-x] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Accepted: 03/28/2014] [Indexed: 11/26/2022]
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The thuEFGKAB operon of rhizobia and agrobacterium tumefaciens codes for transport of trehalose, maltitol, and isomers of sucrose and their assimilation through the formation of their 3-keto derivatives. J Bacteriol 2013; 195:3797-807. [PMID: 23772075 DOI: 10.1128/jb.00478-13] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The thu operon (thuEFGKAB) in Sinorhizobium meliloti codes for transport and utilization functions of the disaccharide trehalose. Sequenced genomes of members of the Rhizobiaceae reveal that some rhizobia and Agrobacterium possess the entire thu operon in similar organizations and that Mesorhizobium loti MAFF303099 lacks the transport (thuEFGK) genes. In this study, we show that this operon is dedicated to the transport and assimilation of maltitol and isomers of sucrose (leucrose, palatinose, and trehalulose) in addition to trehalulose, not only in S. meliloti but also in Agrobacterium tumefaciens. By using genetic complementation, we show that the thuAB genes of S. meliloti, M. loti, and A. tumefaciens are functionally equivalent. Further, we provide both genetic and biochemical evidence to show that these bacteria assimilate these disaccharides by converting them to their respective 3-keto derivatives and that the thuAB genes code for this ketodisaccharide-forming enzyme(s). Formation of 3-ketotrehalose in real time in live S. meliloti is shown through Raman spectroscopy. The presence of an additional ketodisaccharide-forming pathway(s) in A. tumefaciens is also indicated. To our knowledge, this is the first report to identify the genes that code for the conversion of disaccharides to their 3-ketodisaccharide derivatives in any organism.
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DeCoste NJ, Gadkar VJ, Filion M. Verticillium dahliae alters Pseudomonas spp. populations and HCN gene expression in the rhizosphere of strawberry. Can J Microbiol 2011; 56:906-15. [PMID: 21076481 DOI: 10.1139/w10-080] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The production of hydrogen cyanide (HCN) by beneficial root-associated bacteria is an important mechanism for the biological control of plant pathogens. However, little is known about the biotic factors affecting HCN gene expression in the rhizosphere of plants. In this study, real-time reverse transcription PCR (qRT-PCR) assays were developed to investigate the effect of the plant pathogen Verticillium dahliae on hcnC (encoding for HCN biosynthesis) gene expression in Pseudomonas sp. LBUM300. Strawberry plants were inoculated with Pseudomonas sp. LBUM300 and (or) V. dahliae and grown in pots filled with nonsterilized field soil. RNA was extracted from rhizosphere soil sampled at 0, 15, 30, and 45 days following inoculation with V. dahliae and used for qRT-PCR analyses. Populations of V. dahliae and Pseudomonas sp. LBUM300 were also monitored using a culture-independent qPCR approach. hcnC expression was detected at all sampling dates. The presence of V. dahliae had a significant stimulation effect on hcnC gene expression and also increased the population of Pseudomonas sp. LBUM300. However, the V. dahliae population was not altered by the presence of Pseudomonas sp. LBUM300. To our knowledge, this study is the first to evaluate the effect of a plant pathogen on HCN gene expression in the rhizosphere soil.
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Affiliation(s)
- Nadine J DeCoste
- Université de Moncton, Department of Biology, Moncton, NB E1A 3E9, Canada
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Deveau A, Brulé C, Palin B, Champmartin D, Rubini P, Garbaye J, Sarniguet A, Frey-Klett P. Role of fungal trehalose and bacterial thiamine in the improved survival and growth of the ectomycorrhizal fungus Laccaria bicolor S238N and the helper bacterium Pseudomonas fluorescens BBc6R8. ENVIRONMENTAL MICROBIOLOGY REPORTS 2010; 2:560-568. [PMID: 23766226 DOI: 10.1111/j.1758-2229.2010.00145.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The mycorrhiza helper bacterial strain Pseudomonas fluorescens BBc6R8 enhances the establishment of Laccaria bicolor S238N ectomycorrhizae by improving the pre-symbiotic growth and survival of the fungus. Nothing is known about the effect of the ectomycorrhizal fungus on the helper bacteria or the molecules that are involved in the interaction. In this study, we have monitored the population density of the helper strain P. fluorescens BBc6R8 in soils inoculated with L. bicolor and in control soils and found that the ectomycorhizal fungus improves the survival of the helper bacteria. We investigated the identity of the fungal and bacterial metabolites involved in this reciprocal growth-promoting effect using a combination of growth measurements, chemoattractant assays, HPLC and in silico genome analyses. We showed that trehalose, a disaccharide that accumulates to high levels in the fungal hyphae, chemoattracted and promoted the growth of the helper bacteria. Meanwhile, P. fluorescens BBc6R8 produced thiamine at concentrations that enhanced the fungal growth in vitro. Altogether our data indicate that the interaction between the two microorganisms is beneficial for both species and relies, at least in part, on trophic mutualism.
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Affiliation(s)
- A Deveau
- INRA, UMR1136 INRA-Nancy Université«Interactions Arbres/Micro-organismes», Centre de Nancy, IFR110, 54280 Champenoux, France. SRSMC (Structure et Réactivité des Systèmes Moléculaires Complexes) UMR7565, Université Henri Poincaré- Nancy 1, Nancy-Université, France. INRA, UMR1099 'Biologie des Organismes et des Populations appliquée à la Protection des Plantes', 35 653 Le Rheu Cedex, France
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Sturz AV, Peters RD, Carter MR, Sanderson JB, Matheson BG, Christie BR. Variation in antibiosis ability, against potato pathogens, of bacterial communities recovered from the endo- and exoroots of potato crops produced under conventional versus minimum tillage systems. Can J Microbiol 2006; 51:643-54. [PMID: 16234863 DOI: 10.1139/w05-041] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The culturable component of bacterial communities found in the endoroot and associated exoroot (root zone soil) was examined in potatoes (Solanum tuberosum L.) grown under either conventional or minimum tillage systems. Bacterial species--abundance relationships were determined and in vitro antibiosis ability investigated to discover whether tillage practice or bacteria source (endo- or exoroot) influenced bacterial community structure and functional versatility. Antibiosis abilities against Phytophthora erythroseptica Pethyb. (causal agent of pink rot of potatoes), Streptomyces scabies (Thaxt.) Waksm. and Henrici) (causal agent of potato common scab), and Fusarium oxysporum Schlecht. Emend. Snyder and Hansen (causal agent of fusarium potato wilt) were selected as indicators of functional versatility. Bacterial community species richness and diversity indices were significantly greater (P = 0.001) in the exoroot than in the endoroot. While both endo- and exoroot communities possessed antibiosis ability against the phytopathogens tested, a significantly greater proportion (P = 0.0001) of the endoroot population demonstrated antibiosis ability than its exoroot counterpart against P. erythroseptica and F. oxysporum. Tillage regime had no significant influence on species-abundance relationships in the endo- or exoroot but did influence the relative antibiosis ability of bacteria in in vitro challenges against S. scabies, where bacteria sourced from minimum tillage systems were more likely to have antibiosis ability (P = 0.0151). We postulate that the difference in the frequency of isolates with antibiosis ability among endoroot versus exoroot populations points to the adaptation of endophytic bacterial communities that favour plant host defence against pathogens that attack the host systemically.
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Affiliation(s)
- A V Sturz
- Prince Edward Island Department of Agriculture, Fisheries, and Aquaculture, Charlottetown, Canada.
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Monti MR, Smania AM, Fabro G, Alvarez ME, Argaraña CE. Engineering Pseudomonas fluorescens for biodegradation of 2,4-dinitrotoluene. Appl Environ Microbiol 2006; 71:8864-72. [PMID: 16332883 PMCID: PMC1317424 DOI: 10.1128/aem.71.12.8864-8872.2005] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Using the genes encoding the 2,4-dinitrotoluene degradation pathway enzymes, the nonpathogenic psychrotolerant rhizobacterium Pseudomonas fluorescens ATCC 17400 was genetically modified for degradation of this priority pollutant. First, a recombinant strain designated MP was constructed by conjugative transfer from Burkholderia sp. strain DNT of the pJS1 megaplasmid, which contains the dnt genes for 2,4-dinitrotoluene degradation. This strain was able to grow on 2,4-dinitrotoluene as the sole source of carbon, nitrogen, and energy at levels equivalent to those of Burkholderia sp. strain DNT. Nevertheless, loss of the 2,4-dinitrotoluene degradative phenotype was observed for strains carrying pJS1. The introduction of dnt genes into the P.fluorescens ATCC 17400 chromosome, using a suicide chromosomal integration Tn5-based delivery plasmid system, generated a degrading strain that was stable for a long time, which was designated RE. This strain was able to use 2,4-dinitrotoluene as a sole nitrogen source and to completely degrade this compound as a cosubstrate. Furthermore, P. fluorescens RE, but not Burkholderia sp. strain DNT, was capable of degrading 2,4-dinitrotoluene at temperatures as low as 10 degrees C. Finally, the presence of P. fluorescens RE in soils containing levels of 2,4-dinitrotoluene lethal to plants significantly decreased the toxic effects of this nitro compound on Arabidopsis thaliana growth. Using synthetic medium culture, P. fluorescens RE was found to be nontoxic for A.thaliana and Nicotiana tabacum, whereas under these conditions Burkholderia sp. strain DNT inhibited A.thaliana seed germination and was lethal to plants. These features reinforce the advantageous environmental robustness of P. fluorescens RE compared with Burkholderia sp. strain DNT.
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Affiliation(s)
- Mariela R Monti
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000, Córdoba, Argentina
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Jensen JB, Ampomah OY, Darrah R, Peters NK, Bhuvaneswari TV. Role of trehalose transport and utilization in Sinorhizobium meliloti--alfalfa interactions. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2005; 18:694-702. [PMID: 16042015 DOI: 10.1094/mpmi-18-0694] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Genes thuA and thuB in Sinorhizobium meliloti Rm1021 code for a major pathway for trehalose catabolism and are induced by trehalose but not by related structurally similar disaccharides like sucrose or maltose. S. meliloti strains mutated in either of these two genes were severely impaired in their ability to grow on trehalose as the sole source of carbon. ThuA and ThuB show no homology to any known enzymes in trehalose utilization. ThuA has similarity to proteins of unknown function in Mesorhizobium loti, Agrobacterium tumefaciens, and Brucella melitensis, and ThuB possesses homology to dehydrogenases containing the consensus motif AGKHVXCEKP. thuAB genes are expressed in bacteria growing on the root surface and in the infection threads but not in the symbiotic zone of the nodules. Even though thuA and thuB mutants were impaired in competitive colonization of Medicago sativa roots, these strains were more competitive than the wild-type Rml021 in infecting alfalfa roots and forming nitrogen-fixing nodules. Possible reasons for their increased competitiveness are discussed.
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Affiliation(s)
- John Beck Jensen
- Department of Biology, Faculty of Science, University of Tromsø, N-9037 Tromsø, Norway
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Duffy B, Keel C, Défago G. Potential role of pathogen signaling in multitrophic plant-microbe interactions involved in disease protection. Appl Environ Microbiol 2004; 70:1836-42. [PMID: 15006813 PMCID: PMC368418 DOI: 10.1128/aem.70.3.1836-1842.2004] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2002] [Accepted: 11/25/2003] [Indexed: 11/20/2022] Open
Abstract
Multitrophic interactions mediate the ability of fungal pathogens to cause plant disease and the ability of bacterial antagonists to suppress disease. Antibiotic production by antagonists, which contributes to disease suppression, is known to be modulated by abiotic and host plant environmental conditions. Here, we demonstrate that a pathogen metabolite functions as a negative signal for bacterial antibiotic biosynthesis, which can determine the relative importance of biological control mechanisms available to antagonists and which may also influence fungus-bacterium ecological interactions. We found that production of the polyketide antibiotic 2,4-diacetylphloroglucinol (DAPG) was the primary biocontrol mechanism of Pseudomonas fluorescens strain Q2-87 against Fusarium oxysporum f. sp. radicis-lycopersici on the tomato as determined with mutational analysis. In contrast, DAPG was not important for the less-disease-suppressive strain CHA0. This was explained by differential sensitivity of the bacteria to fusaric acid, a pathogen phyto- and mycotoxin that specifically blocked DAPG biosynthesis in strain CHA0 but not in strain Q2-87. In CHA0, hydrogen cyanide, a biocide not repressed by fusaric acid, played a more important role in disease suppression.
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Affiliation(s)
- Brion Duffy
- Swiss Federal Research Institute for Fruit Production, Viticulture and Horticulture, CH-8820 Wädenswil, Switzerland.
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Duffy B, Schouten A, Raaijmakers JM. Pathogen self-defense: mechanisms to counteract microbial antagonism,. ANNUAL REVIEW OF PHYTOPATHOLOGY 2003; 41:501-538. [PMID: 12730392 DOI: 10.1146/annurev.phyto.41.052002.095606] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Natural and agricultural ecosystems harbor a wide variety of microorganisms that play an integral role in plant health, crop productivity, and preservation of multiple ecosystem functions. Interactions within and among microbial communities are numerous and range from synergistic and mutualistic to antagonistic and parasitic. Antagonistic and parasitic interactions have been exploited in the area of biological control of plant pathogenic microorganisms. To date, biocontrol is typically viewed from the perspective of how antagonists affect pathogens. This review examines the other face of this interaction: how plant pathogens respond to antagonists and how this can affect the efficacy of biocontrol. Just as microbial antagonists utilize a diverse arsenal of mechanisms to dominate interactions with pathogens, pathogens have surprisingly diverse responses to counteract antagonism. These responses include detoxification, repression of biosynthetic genes involved in biocontrol, active efflux of antibiotics, and antibiotic resistance. Understanding pathogen self-defense mechanisms for coping with antagonist assault provides a novel approach to improving the durability of biologically based disease control strategies and has implications for the deployment of transgenes (microorganisms or plants).
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Affiliation(s)
- Brion Duffy
- Swiss Federal Research Center for Fruit Production, Viticulture and Horticulture, FAW, Postfach 185, CH-8820 Wadenswil, Switzerland.
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Haas D, Keel C. Regulation of antibiotic production in root-colonizing Peudomonas spp. and relevance for biological control of plant disease. ANNUAL REVIEW OF PHYTOPATHOLOGY 2003; 41:117-53. [PMID: 12730389 DOI: 10.1146/annurev.phyto.41.052002.095656] [Citation(s) in RCA: 365] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Certain strains of fluorescent pseudomonads are important biological components of agricultural soils that are suppressive to diseases caused by pathogenic fungi on crop plants. The biocontrol abilities of such strains depend essentially on aggressive root colonization, induction of systemic resistance in the plant, and the production of diffusible or volatile antifungal antibiotics. Evidence that these compounds are produced in situ is based on their chemical extraction from the rhizosphere and on the expression of antibiotic biosynthetic genes in the producer strains colonizing plant roots. Well-characterized antibiotics with biocontrol properties include phenazines, 2,4-diacetylphloroglucinol, pyoluteorin, pyrrolnitrin, lipopeptides, and hydrogen cyanide. In vitro, optimal production of these compounds occurs at high cell densities and during conditions of restricted growth, involving (i) a number of transcriptional regulators, which are mostly pathway-specific, and (ii) the GacS/GacA two-component system, which globally exerts a positive effect on the production of extracellular metabolites at a posttranscriptional level. Small untranslated RNAs have important roles in the GacS/GacA signal transduction pathway. One challenge in future biocontrol research involves development of new strategies to overcome the broad toxicity and lack of antifungal specificity displayed by most biocontrol antibiotics studied so far.
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Affiliation(s)
- Dieter Haas
- Institut de Microbiologie Fondamentale, Universite de Lausanne, CH-1015 Lausanne, Switzerland;
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Notz R, Maurhofer M, Schnider-Keel U, Duffy B, Haas D, Défago G. Biotic Factors Affecting Expression of the 2,4-Diacetylphloroglucinol Biosynthesis Gene phlA in Pseudomonas fluorescens Biocontrol Strain CHA0 in the Rhizosphere. PHYTOPATHOLOGY 2001; 91:873-881. [PMID: 18944233 DOI: 10.1094/phyto.2001.91.9.873] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
ABSTRACT Production of the polyketide antimicrobial metabolite 2,4-diacetyl-phloroglucinol (DAPG) is a key factor in the biocontrol activity of Pseudomonas fluorescens CHA0. Strain CHA0 carrying a translational phlA'-'lacZ fusion was used to monitor expression of the phl biosynthetic genes in vitro and in the rhizosphere. Expression of the reporter gene accurately reflected actual production of DAPG in vitro and in planta as determined by direct extraction of the antimicrobial compound. In a gnotobiotic system containing a clay and sand-based artificial soil, reporter gene expression was significantly greater in the rhizospheres of two monocots (maize and wheat) compared with gene expression in the rhizospheres of two dicots (bean and cucumber). We observed this host genotype effect on bacterial gene expression also at the level of cultivars. Significant differences were found among six additional maize cultivars tested under gnotobiotic conditions. There was no difference between transgenic maize expressing the Bacillus thuringiensis insecticidal gene cry1Ab and the near-isogenic parent line. Plant age had a significant impact on gene expression. Using maize as a model, expression of the phlA'-'lacZ reporter gene peaked at 24 h after planting of pregerminated seedlings, and dropped to a fourth of that value within 48 h, remaining at that level throughout 22 days of plant growth. Root infection by Pythium ultimum stimulated bacterial gene expression on both cucumber and maize, and this was independent of differences in rhizosphere colonization on these host plants. To our knowledge, this is the first comprehensive evaluation of how biotic factors that commonly confront bacterial inoculants in agricultural systems (host genotype, host age, and pathogen infection) modulate the expression of key biocontrol genes for disease suppression.
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Raaijmakers JM, Weller DM. Exploiting genotypic diversity of 2,4-diacetylphloroglucinol-producing Pseudomonas spp.: characterization of superior root-colonizing P. fluorescens strain Q8r1-96. Appl Environ Microbiol 2001; 67:2545-54. [PMID: 11375162 PMCID: PMC92906 DOI: 10.1128/aem.67.6.2545-2554.2001] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The genotypic diversity that occurs in natural populations of antagonistic microorganisms provides an enormous resource for improving biological control of plant diseases. In this study, we determined the diversity of indigenous 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. occurring on roots of wheat grown in a soil naturally suppressive to take-all disease of wheat. Among 101 isolates, 16 different groups were identified by random amplified polymorphic DNA (RAPD) analysis. One RAPD group made up 50% of the total population of DAPG-producing Pseudomonas spp. Both short- and long-term studies indicated that this dominant genotype, exemplified by P. fluorescens Q8r1-96, is highly adapted to the wheat rhizosphere. Q8r1-96 requires a much lower dose (only 10 to 100 CFU seed(-1) or soil(-1)) to establish high rhizosphere population densities (10(7) CFU g of root(-1)) than Q2-87 and 1M1-96, two genotypically different, DAPG-producing P. fluorescens strains. Q8r1-96 maintained a rhizosphere population density of approximately 10(5) CFU g of root(-1) after eight successive growth cycles of wheat in three different, raw virgin soils, whereas populations of Q2-87 and 1M1-96 dropped relatively quickly after five cycles and were not detectable after seven cycles. In short-term studies, strains Q8r1-96, Q2-87, and 1M1-96 did not differ in their ability to suppress take-all. After eight successive growth cycles, however, Q8r1-96 still provided control of take-all to the same level as obtained in the take-all suppressive soil, whereas Q2-87 and 1M1-96 gave no control anymore. Biochemical analyses indicated that the superior rhizosphere competence of Q8r1-96 is not related to in situ DAPG production levels. We postulate that certain rhizobacterial genotypes have evolved a preference for colonization of specific crops. By exploiting diversity of antagonistic rhizobacteria that share a common trait, biological control can be improved significantly.
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Affiliation(s)
- J M Raaijmakers
- Root Disease and Biological Control Research Unit, USDA-ARS, Washington State University, Pullman, Washington 99164-6430, USA. jos.raaijmakers@
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16
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Reignault PH, Cogan A, Muchembled J, Lounes-Hadj Sahraoui A, Durand R, Sancholle M. Trehalose induces resistance to powdery mildew in wheat. THE NEW PHYTOLOGIST 2001; 149:519-529. [PMID: 33873340 DOI: 10.1046/j.1469-8137.2001.00035.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
• Reduction in the degree of powdery mildew infection of wheat leaves is observed after treatments with trehalose, a nonreducing disaccharide commonly found in a wide variety of organisms, including fungi. • Wheat (Triticum aestivum) cv. Sideral plants grown in phytotrons were inoculated with Blumeria graminis f.sp. tritici. In addition to degree of infection, the effect of trehalose solution was further investigated using light and fluorescence microscopy and enzyme assays. • Infection in wheat leaves was reduced by 50 and 95% with trehalose solution (15 g l-1 ) following a single spraying and three sprayings, respectively; in a detached leaf assay, trehalose was effective at concentrations as low as 0.01 g l-1 . Trehalose did not inhibit conidial germination and differentiation of appressoria (in vitro or on the leaf epidermis), but enhanced papilla deposition in epidermal cells. Trehalose also enhanced phenylalanine ammonia-lyase (PAL) and peroxidase (PO) activities; both markers of plant defence responses. However, the level of three cinnamyl alcohol dehydrogenase (CAD) activities (conyferyl, p-coumaryl and sinapyl alcohol dehydrogenase) was unchanged. • Trehalose treatment of wheat confers resistance to B. graminis infection by activating plant defence responses (e.g. papilla deposition, PAL and PO activities).
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Affiliation(s)
- P H Reignault
- Mycologie-Phytopathologie-Environnement, Université du Littoral Côte d'Opale, 17 avenue Louis Blériot, BP 699, F-62228 Calais cedex, France
| | - A Cogan
- Mycologie-Phytopathologie-Environnement, Université du Littoral Côte d'Opale, 17 avenue Louis Blériot, BP 699, F-62228 Calais cedex, France
| | - J Muchembled
- Mycologie-Phytopathologie-Environnement, Université du Littoral Côte d'Opale, 17 avenue Louis Blériot, BP 699, F-62228 Calais cedex, France
| | - A Lounes-Hadj Sahraoui
- Mycologie-Phytopathologie-Environnement, Université du Littoral Côte d'Opale, 17 avenue Louis Blériot, BP 699, F-62228 Calais cedex, France
| | - R Durand
- Mycologie-Phytopathologie-Environnement, Université du Littoral Côte d'Opale, 17 avenue Louis Blériot, BP 699, F-62228 Calais cedex, France
| | - M Sancholle
- Mycologie-Phytopathologie-Environnement, Université du Littoral Côte d'Opale, 17 avenue Louis Blériot, BP 699, F-62228 Calais cedex, France
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17
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Abstract
The loss of organic material from the roots provides the energy for the development of active microbial populations in the rhizosphere around the root. Generally, saproptrophs or biotrophs such as mycorrhizal fungi grow in the rhizosphere in response to this carbon loss, but plant pathogens may also develop and infect a susceptible host, resulting in disease. This review examines the microbial interactions that can take place in the rhizosphere and that are involved in biological disease control. The interactions of bacteria used as biocontrol agents of bacterial and fungal plant pathogens, and fungi used as biocontrol agents of protozoan, bacterial and fungal plant pathogens are considered. Whenever possible, modes of action involved in each type of interaction are assessed with particular emphasis on antibiosis, competition, parasitism, and induced resistance. The significance of plant growth promotion and rhizosphere competence in biocontrol is also considered. Multiple microbial interactions involving bacteria and fungi in the rhizosphere are shown to provide enhanced biocontrol in many cases in comparison with biocontrol agents used singly. The extreme complexity of interactions that can occur in the rhizosphere is highlighted and some potential areas for future research in this area are discussed briefly.
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Affiliation(s)
- J M Whipps
- Plant Pathology and Microbiology Department, Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK.
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18
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Matthijs S, Koedam N, Cornelis P, De Greve H. The trehalose operon of Pseudomonas fluorescens ATCC 17400. Res Microbiol 2000; 151:845-51. [PMID: 11191810 DOI: 10.1016/s0923-2508(00)01151-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The trehalose operon of Pseudomonas fluorescens ATCC 17400 consists of treP, treA and treR. The gene treP codes for a putative enzyme II subunit of the phosphotransferase system that catalyzes the phosphorylation of trehalose together with its translocation across the cell membrane and treA encodes a putative phosphotrehalase, which hydrolyzes the incoming trehalose-6-phosphate into glucose and glucose-6-phosphate. Both genes are negatively regulated by TreR, a repressor of the FadR-GntR family of transcription regulators. The operon that is induced by trehalose present in the medium shows a high similarity both in the function of genes and in the regulation with the trehalose operon of Bacillus subtilis.
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Affiliation(s)
- S Matthijs
- Laboratorium Microbiële Interacties, Vrije Universiteit Brussel, Sint-Genesius-Rode, Belgium
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19
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Duffy BK, Défago G. Environmental factors modulating antibiotic and siderophore biosynthesis by Pseudomonas fluorescens biocontrol strains. Appl Environ Microbiol 1999; 65:2429-38. [PMID: 10347023 PMCID: PMC91358 DOI: 10.1128/aem.65.6.2429-2438.1999] [Citation(s) in RCA: 206] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/1998] [Accepted: 03/22/1999] [Indexed: 11/20/2022] Open
Abstract
Understanding the environmental factors that regulate the biosynthesis of antimicrobial compounds by disease-suppressive strains of Pseudomonas fluorescens is an essential step toward improving the level and reliability of their biocontrol activity. We used liquid culture assays to identify several minerals and carbon sources which had a differential influence on the production of the antibiotics 2,4-diacetylphloroglucinol (PHL), pyoluteorin (PLT), and pyrrolnitrin and the siderophores salicylic acid and pyochelin by the model strain CHA0, which was isolated from a natural disease-suppressive soil in Switzerland. Production of PHL was stimulated by Zn2+, NH4Mo2+, and glucose; the precursor compound mono-acetylphloroglucinol was stimulated by the same factors as PHL. Production of PLT was stimulated by Zn2+, Co2+, and glycerol but was repressed by glucose. Pyrrolnitrin production was increased by fructose, mannitol, and a mixture of Zn2+ and NH4Mo2+. Pyochelin production was increased by Co2+, fructose, mannitol, and glucose. Interestingly, production of its precursor salicylic acid was increased by different factors, i.e., NH4Mo2+, glycerol, and glucose. The mixture of Zn2+ and NH4Mo2+ with fructose, mannitol, or glycerol further enhanced the production of PHL and PLT compared with either the minerals or the carbon sources used alone, but it did not improve siderophore production. Extending fermentation time from 2 to 5 days increased the accumulation of PLT, pyrrolnitrin, and pyochelin but not of PHL. When findings with CHA0 were extended to an ecologically and genetically diverse collection of 41 P. fluorescens biocontrol strains, the effect of certain factors was strain dependent, while others had a general effect. Stimulation of PHL by Zn2+ and glucose was strain dependent, whereas PLT production by all strains that can produce this compound was stimulated by Zn2+ and transiently repressed by glucose. Inorganic phosphate reduced PHL production by CHA0 and seven other strains tested but to various degrees. Production of PLT but not pyrrolnitrin by CHA0 was also reduced by 100 mM phosphate. The use of 1/10-strength nutrient broth-yeast extract, compared with standard nutrient broth-yeast extract, amended with glucose and/or glycerol resulted in dramatically increased accumulations of PHL (but not PLT), pyochelin, and salicylic acid, indicating that the ratio of carbon source to nutrient concentration played a key role in the metabolic flow. The results of this study (i) provide insight into the biosynthetic regulation of antimicrobial compounds, (ii) limit the number of factors for intensive study in situ, and (iii) indicate factors that can be manipulated to improve bacterial inoculants.
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Affiliation(s)
- B K Duffy
- Phytopathology Group, Institute of Plant Sciences, Swiss Federal Institute of Technology, CH-8092 Zürich, Switzerland.
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