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Joyce E. Loper - One of the best experts on this subject based on the ideXlab platform.

  • An Interspecies Signaling System Mediated by Fusaric Acid Has Parallel Effects on Antifungal Metabolite Production by Pseudomonas protegens Strain Pf-5 and Antibiosis of Fusarium spp.
    Applied and environmental microbiology, 2015
    Co-Authors: Maria Carolina Quecine, Marcella D. Henkels, Brenda T. Shaffer, Teresa A. Kidarsa, Neal C. Goebel, T. Mark Zabriskie, Joyce E. Loper
    Abstract:

    Pseudomonas protegens strain Pf-5 is a Rhizosphere Bacterium that suppresses soilborne plant diseases and produces at least seven different secondary metabolites with antifungal properties. We derived mutants of Pf-5 with single and multiple mutations in biosynthesis genes for seven antifungal metabolites: 2,4-diacetylphoroglucinol (DAPG), pyrrolnitrin, pyoluteorin, hydrogen cyanide, rhizoxin, orfamide A, and toxoflavin. These mutants were tested for inhibition of the pathogens Fusarium verticillioides and Fusarium oxysporum f. sp. pisi. Rhizoxin, pyrrolnitrin, and DAPG were found to be primarily responsible for fungal antagonism by Pf-5. Previously, other workers showed that the mycotoxin fusaric acid, which is produced by many Fusarium species, including F. verticillioides, inhibited the production of DAPG by Pseudomonas spp. In this study, amendment of culture media with fusaric acid decreased DAPG production, increased pyoluteorin production, and had no consistent influence on pyrrolnitrin or orfamide A production by Pf-5. Fusaric acid also altered the transcription of biosynthetic genes, indicating that the mycotoxin influenced antibiotic production by Pf-5 at the transcriptional level. Addition of fusaric acid to the culture medium reduced antibiosis of F. verticillioides by Pf-5 and derivative strains that produce DAPG but had no effect on antibiosis by Pf-5 derivatives that suppressed F. verticillioides due to pyrrolnitrin or rhizoxin production. Our results demonstrated the importance of three compounds, rhizoxin, pyrrolnitrin, and DAPG, in suppression of Fusarium spp. by Pf-5 and confirmed that an interspecies signaling system mediated by fusaric acid had parallel effects on antifungal metabolite production and antibiosis by the bacterial biological control organism.

  • the genomic sequence of pseudomonas fluorescens pf 5 insights into biological control
    Phytopathology, 2007
    Co-Authors: Joyce E. Loper, Donald Y Kobayashi, Ian T Paulsen
    Abstract:

    Loper, J. E., Kobayashi, D. Y., and Paulsen, I. T. 2007. The genomic sequence of Pseudomonas fluorescens Pf-5: Insights into biological control. Phytopathology 97:233-238. The complete sequence of the 7.07 Mb genome of the biological control agent Pseudomonas fluorescens Pf-5 is now available, providing a new opportunity to advance knowledge of biological control through genomics. P. fluorescens Pf-5 is a Rhizosphere Bacterium that suppresses seedling emergence diseases and produces a spectrum of antibiotics toxic to plant-pathogenic fungi and oomycetes. In addition to six known secondary metabolites produced by Pf-5, three novel secondary metabolite biosynthesis gene clusters identified in the genome could also contribute to biological control. The genomic sequence provides numerous clues as to mechanisms used by the Bacterium to survive in the spermosphere and Rhizosphere. These features include broad catabolic and transport capabilities for utilizing seed and root exudates, an expanded collection of efflux systems for defense against environmental stress and microbial competition, and the presence of 45 outer membrane receptors that should allow for the uptake of iron from a wide array of siderophores produced by soil microorganisms. As expected for a Bacterium with a large genome that lives in a rapidly changing environment, Pf-5 has an extensive collection of regulatory genes, only some of which have been characterized for their roles in regulation of secondary metabolite production or biological control. Consistent with its commensal lifestyle, Pf-5 appears to lack a number of virulence and pathogenicity factors found in plant pathogens.

  • positive autoregulation and signaling properties of pyoluteorin an antibiotic produced by the biological control organism pseudomonas fluorescens pf 5
    Applied and Environmental Microbiology, 2004
    Co-Authors: Marion Brodhagen, Joyce E. Loper, Marcella D. Henkels
    Abstract:

    Pseudomonas fluorescens Pf-5, a Rhizosphere Bacterium, produces a suite of secondary metabolites that are toxic to seed- and root-rotting plant pathogens. Among these are the polyketide compounds pyoluteorin and 2,4-diacetylphloroglucinol. We provide evidence that pyoluteorin production is influenced by positive autoregulation. Addition of pyoluteorin to liquid cultures of Pf-5 enhanced pyoluteorin production. In addition, pyoluteorin and 2,4-diacetylphloroglucinol mutually inhibit one another's production in Pf-5. For pyoluteorin, both positive autoregulation and negative influences on production by 2,4-diacetylphloroglucinol were demonstrated at the transcriptional level by measuring activity from transcriptional fusions of an ice nucleation reporter gene (inaZ) to three separate pyoluteorin biosynthetic genes. The occurrence of pyoluteorin autoregulation in the Rhizosphere was assessed on cucumber seedlings in pasteurized soil with cross-feeding experiments. In the Rhizosphere, expression of a pyoluteorin biosynthesis gene by a pyoluteorin-deficient mutant of Pf-5 was enhanced by pyoluteorin produced by coinoculated cells of Pf-5. These data establish that the polyketide pyoluteorin is an autoregulatory compound and functions as a signal molecule influencing the spectrum of secondary metabolites produced by the bacterial cell.

Dieter Haas - One of the best experts on this subject based on the ideXlab platform.

  • three small rnas jointly ensure secondary metabolism and biocontrol in pseudomonas fluorescens cha0
    Proceedings of the National Academy of Sciences of the United States of America, 2005
    Co-Authors: Christophe Dubuis, Dieter Haas
    Abstract:

    In many Gram-negative bacteria, the GacS/GacA two-component system positively controls the expression of extracellular products or storage compounds. In the plant-beneficial Rhizosphere Bacterium Pseudomonas fluorescens CHA0, the GacS/GacA system is essential for the production of antibiotic compounds and hence for biological control of root-pathogenic fungi. The small (119-nt) RNA RsmX discovered in this study, together with RsmY and RsmZ, forms a triad of GacA-dependent small RNAs, which sequester the RNA-binding proteins RsmA and RsmE and thereby antagonize translational repression exerted by these proteins in strain CHA0. This small RNA triad was found to be both necessary and sufficient for posttranscriptional derepression of biocontrol factors and for protection of cucumber from Pythium ultimum. The same three small RNAs also positively regulated swarming motility and the synthesis of a quorum-sensing signal, which is unrelated to N-acyl-homoserine lactones, and which autoinduces the Gac/Rsm cascade. Expression of RsmX and RsmY increased in parallel throughout cell growth, whereas RsmZ was produced during the late growth phase. This differential expression is assumed to facilitate fine tuning of GacS/A-controlled cell population density-dependent regulation in P. fluorescens.

  • three small rnas jointly ensure secondary metabolism and biocontrol in pseudomonas fluorescens cha0
    Proceedings of the National Academy of Sciences of the United States of America, 2005
    Co-Authors: Elisabeth Kay, Christophe Dubuis, Dieter Haas
    Abstract:

    In many Gram-negative bacteria, the GacS/GacA two-component system positively controls the expression of extracellular products or storage compounds. In the plant-beneficial Rhizosphere Bacterium Pseudomonas fluorescens CHA0, the GacS/GacA system is essential for the production of antibiotic compounds and hence for biological control of root-pathogenic fungi. The small (119-nt) RNA RsmX discovered in this study, together with RsmY and RsmZ, forms a triad of GacA-dependent small RNAs, which sequester the RNA-binding proteins RsmA and RsmE and thereby antagonize translational repression exerted by these proteins in strain CHA0. This small RNA triad was found to be both necessary and sufficient for posttranscriptional derepression of biocontrol factors and for protection of cucumber from Pythium ultimum. The same three small RNAs also positively regulated swarming motility and the synthesis of a quorum-sensing signal, which is unrelated to N-acyl-homoserine lactones, and which autoinduces the Gac/Rsm cascade. Expression of RsmX and RsmY increased in parallel throughout cell growth, whereas RsmZ was produced during the late growth phase. This differential expression is assumed to facilitate fine tuning of GacS/A-controlled cell population density-dependent regulation in P. fluorescens.

Stijn Spaepen - One of the best experts on this subject based on the ideXlab platform.

  • Transcriptome Analysis of the Rhizosphere Bacterium Azospirillum brasilense Reveals an Extensive Auxin Response
    Microbial Ecology, 2011
    Co-Authors: Sandra Van Puyvelde, Lore Cloots, Kristof Engelen, Kathleen Marchal, Jos Vanderleyden, Stijn Spaepen
    Abstract:

    The Rhizosphere Bacterium Azospirillum brasilense produces the auxin indole-3-acetic acid (IAA) through the indole-3-pyruvate pathway. As we previously demonstrated that transcription of the indole-3-pyruvate decarboxylase ( ipdC ) gene is positively regulated by IAA, produced by A. brasilense itself or added exogenously, we performed a microarray analysis to study the overall effects of IAA on the transcriptome of A. brasilense . The transcriptomes of A. brasilense wild-type and the ipdC knockout mutant, both cultured in the absence and presence of exogenously added IAA, were compared. Interfering with the IAA biosynthesis/homeostasis in A. brasilense through inactivation of the ipdC gene or IAA addition results in much broader transcriptional changes than anticipated. Based on the multitude of changes observed by comparing the different transcriptomes, we can conclude that IAA is a signaling molecule in A. brasilense . It appears that the Bacterium, when exposed to IAA, adapts itself to the plant Rhizosphere, by changing its arsenal of transport proteins and cell surface proteins. A striking example of adaptation to IAA exposure, as happens in the Rhizosphere, is the upregulation of a type VI secretion system (T6SS) in the presence of IAA. The T6SS is described as specifically involved in Bacterium–eukaryotic host interactions. Additionally, many transcription factors show an altered regulation as well, indicating that the regulatory machinery of the Bacterium is changing.

  • transcriptome analysis of the Rhizosphere Bacterium azospirillum brasilense reveals an extensive auxin response
    Microbial Ecology, 2011
    Co-Authors: Sandra Van Puyvelde, Lore Cloots, Kristof Engelen, Kathleen Marchal, Jos Vanderleyden, Stijn Spaepen
    Abstract:

    The Rhizosphere Bacterium Azospirillum brasilense produces the auxin indole-3-acetic acid (IAA) through the indole-3-pyruvate pathway. As we previously demonstrated that transcription of the indole-3-pyruvate decarboxylase (ipdC) gene is positively regulated by IAA, produced by A. brasilense itself or added exogenously, we performed a microarray analysis to study the overall effects of IAA on the transcriptome of A. brasilense. The transcriptomes of A. brasilense wild-type and the ipdC knockout mutant, both cultured in the absence and presence of exogenously added IAA, were compared.

Gabriele Berg - One of the best experts on this subject based on the ideXlab platform.

  • quorum sensing effects in the antagonistic Rhizosphere Bacterium serratia plymuthica hro c48
    FEMS Microbiology Ecology, 2009
    Co-Authors: Henry Muller, Christian Westendorf, Erich Leitner, Leonid Chernin, Kathrin Riedel, S Schmidt, Leo Eberl, Gabriele Berg
    Abstract:

    The Rhizosphere-associated Bacterium Serratia plymuthica HRO-C48 is not only able to suppress symptoms caused by soil-borne pathogens but is also able to stimulate growth of plants. Detailed knowledge about the underlying mechanisms and regulation are crucial for the application in biocontrol strategies. To analyse the influence of N-acyl homoserine lactone (AHL)-mediated communication on the biocontrol activity, the AHL-degrading lactonase AiiA was heterologously expressed in the strain, resulting in abolished AHL production. The comparative analysis of the wild type and AHL negative mutants led to the identification of new AHL-regulated phenotypes. In the pathosystem Verticillium dahliae-oilseed rape, the essential role of AHL-mediated signaling for disease suppression was demonstrated. In vitro, the regulatory function of AHLs in the synthesis of the plant growth hormone indole-3-acetic acid is shown for the first time. Additionally, swimming motility was found to be negatively AHL regulated. In contrast, production of extracellular hydrolytic enzymes is shown to be positively AHL-regulated. HRO-C48 emits a broad spectrum of volatile organic compounds that are involved in antifungal activity and, interestingly, whose relative abundances are influenced by quorum sensing (QS). This study shows that QS is crucial for biocontrol activity of S. plymuthica and discusses the impact for the application of the strain as a biocontrol agent.

  • bulk and Rhizosphere soil bacterial communities studied by denaturing gradient gel electrophoresis plant dependent enrichment and seasonal shifts revealed
    Applied and Environmental Microbiology, 2001
    Co-Authors: Kornelia Smalla, Gabriele Wieland, Arno Buchner, A Zock, J Parzy, S Kaiser, N Roskot, Holger Heuer, Gabriele Berg
    Abstract:

    The bacterial Rhizosphere communities of three host plants of the pathogenic fungus Verticillium dahliae, field-grown strawberry (Fragaria ananassa Duch.), oilseed rape (Brassica napus L.), and potato (Solanum tuberosum L.), were analyzed. We aimed to determine the degree to which the Rhizosphere effect is plant dependent and whether this effect would be increased by growing the same crops in two consecutive years. Rhizosphere or soil samples were taken five times over the vegetation periods. To allow a cultivation-independent analysis, total community DNA was extracted from the microbial pellet recovered from root or soil samples. 16S rDNA fragments amplified by PCR from soil or Rhizosphere Bacterium DNA were analyzed by denaturing gradient gel electrophoresis (DGGE). The DGGE fingerprints showed plant-dependent shifts in the relative abundance of bacterial populations in the Rhizosphere which became more pronounced in the second year. DGGE patterns of oilseed rape and potato Rhizosphere communities were more similar to each other than to the strawberry patterns. In both years seasonal shifts in the abundance and composition of the bacterial Rhizosphere populations were observed. Independent of the plant species, the patterns of the first sampling times for both years were characterized by the absence of some of the bands which became dominant at the following sampling times. Bacillus megaterium and Arthrobacter sp. were found as predominant populations in bulk soils. Sequencing of dominant bands excised from the Rhizosphere patterns revealed that 6 out of 10 bands resembled gram-positive bacteria. Nocardia populations were identified as strawberry-specific bands.

Volker F Wendisch - One of the best experts on this subject based on the ideXlab platform.

  • inorganic phosphate solubilization by Rhizosphere Bacterium paenibacillus sonchi gene expression and physiological functions
    Frontiers in Microbiology, 2020
    Co-Authors: Luciana F Brito, Marina Gil Lopez, Lucas Straube, Luciane Maria Pereira Passaglia, Volker F Wendisch
    Abstract:

    Due to the importance of phosphorus (P) in agriculture, crop inoculation with phosphate-solubilizing bacteria is a relevant subject of study. Paenibacillus sonchi genomovar Riograndensis SBR5 is a promising candidate for crop inoculation, as it can fix nitrogen and excrete ammonium at a remarkably high rate. However, its trait of phosphate solubilization (PS) has not yet been studied in detail. Here, differential gene expression and functional analyses were performed to characterize PS in this Bacterium. SBR5 was cultivated with two distinct P sources: NaH2PO4 as soluble phosphate source (SPi) and hydroxyapatite as insoluble phosphate source (IPi). Total RNA of SBR5 cultivated in those two conditions was isolated and sequenced, and bacterial growth and product formation were monitored. In the IPi medium, the expression of 68 genes was upregulated, whereas 100 genes were downregulated. Among those, genes involved in carbon metabolism, including those coding for subunits of 2-oxoglutarate dehydrogenase, were identified. Quantitation of organic acids showed that the production of tricarboxylic acid cycle-derived organic acids was reduced in IPi condition, whereas acetate and gluconate were overproduced. Increased concentrations of proline, trehalose, and glycine betaine revealed active osmoprotection during growth in IPi. The cultivation with hydroxyapatite also caused the reduction in the motility of SBR5 cells as a response to Pi depletion at the beginning of its growth. SBR5 was able to solubilize hydroxyapatite, which suggests that this organism is a promising phosphate-solubilizing Bacterium. Our findings are the initial step in the elucidation of the PS process in P. sonchi SBR5 and will be a valuable groundwork for further studies of this organism as a plant growth-promoting rhizoBacterium.