Pseudomonad

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Monika Maurhofer - One of the best experts on this subject based on the ideXlab platform.

  • Oral Insecticidal Activity of Plant-Associated Pseudomonads
    Environmental microbiology, 2012
    Co-Authors: Beat Ruffner, Christoph Keel, Maria Péchy-tarr, Florian Ryffel, Patrik Hoegger, Christian Obrist, Alfred Rindlisbacher, Monika Maurhofer
    Abstract:

    Summary Biocontrol Pseudomonads are most known to protect plants from fungal diseases and to increase plant yield, while intriguing aspects on insecticidal activity have been discovered only recently. Here, we demonstrate that Fit toxin producing Pseudomonads, in contrast to a naturally Fit-deficient strain, exhibit potent oral activity against larvae of Spodoptera littoralis, Heliothis virescens and Plutella xylostella, all major insect pests of agricultural crops. Spraying plant leaves with suspensions containing only 1000 Pseudomonas cells per ml was sufficient to kill 70–80% of Spodoptera and Heliothis larvae. Monitoring survival kinetics and bacterial titres in parallel, we demonstrate that Pseudomonas fluorescens CHA0 and Pseudomonas chlororaphis PCL1391, two bacteria harbouring the Fit gene cluster colonize and kill insects via oral infection. Using Fit mutants of CHA0 and PCL1391, we show that production of the Fit toxin contributes substantially to oral insecticidal activity. Furthermore, the global regulator GacA is required for full insecticidal activity. Our findings demonstrate the lethal oral activity of two root-colonizing Pseudomonads so far known as potent antagonists of fungal plant pathogens. This adds insecticidal activity to the existing biocontrol repertoire of these bacteria and opens new perspectives for applications in crop pest control and in research on their ecological behaviour.

  • pyrroloquinoline quinone biosynthesis gene pqqc a novel molecular marker for studying the phylogeny and diversity of phosphate solubilizing Pseudomonads
    Applied and Environmental Microbiology, 2011
    Co-Authors: Joana Beatrice Meyer, Michele Frapolli, Christoph Keel, Monika Maurhofer
    Abstract:

    Many root-colonizing Pseudomonads are able to promote plant growth by increasing phosphate availability in soil through solubilization of poorly soluble rock phosphates. The major mechanism of phosphate solubilization by Pseudomonads is the secretion of gluconic acid, which requires the enzyme glucose dehydrogenase and its cofactor pyrroloquinoline quinone (PQQ). The main aim of this study was to evaluate whether a PQQ biosynthetic gene is suitable to study the phylogeny of phosphate-solubilizing Pseudomonads. To this end, two new primers, which specifically amplify the pqqC gene of the Pseudomonas genus, were designed. pqqC fragments were amplified and sequenced from a Pseudomonas strain collection and from a natural wheat rhizosphere population using cultivation-dependent and cultivation-independent approaches. Phylogenetic trees based on pqqC sequences were compared to trees obtained with the two concatenated housekeeping genes rpoD and gyrB. For both pqqC and rpoD-gyrB, similar main phylogenetic clusters were found. However, in the pqqC but not in the rpoD-gyrB tree, the group of fluorescent Pseudomonads producing the antifungal compounds 2,4-diacetylphloroglucinol and pyoluteorin was located outside the Pseudomonas fluorescens group. pqqC sequences from isolated Pseudomonads were differently distributed among the identified phylogenetic groups than pqqC sequences derived from the cultivation-independent approach. Comparing pqqC phylogeny and phosphate solubilization activity, we identified one phylogenetic group with high solubilization activity. In summary, we demonstrate that the gene pqqC is a novel molecular marker that can be used complementary to housekeeping genes for studying the diversity and evolution of plant-beneficial Pseudomonads.

  • Interplay between wheat cultivars, biocontrol Pseudomonads, and soil.
    Applied and environmental microbiology, 2010
    Co-Authors: Joana Beatrice Meyer, Geneviève Défago, Michele Frapolli, Christoph Keel, Matthias P. Lutz, Maria Péchy-tarr, Laurène Rochat, Monika Maurhofer
    Abstract:

    There is a significant potential to improve the plant-beneficial effects of root-colonizing Pseudomonads by breeding wheat genotypes with a greater capacity to sustain interactions with these bacteria. However, the interaction between Pseudomonads and crop plants at the cultivar level, as well as the conditions which favor the accumulation of beneficial microorganisms in the wheat rhizosphere, is largely unknown. Therefore, we characterized the three Swiss winter wheat (Triticum aestivum) cultivars Arina, Zinal, and Cimetta for their ability to accumulate naturally occurring plant-beneficial Pseudomonads in the rhizosphere. Cultivar performance was measured also by the ability to select for specific genotypes of 2,4-diacetylphloroglucinol (DAPG) producers in two different soils. Cultivar-specific differences were found; however, these were strongly influenced by the soil type. Denaturing gradient gel electrophoresis (DGGE) analysis of fragments of the DAPG biosynthetic gene phlD amplified from natural Pseudomonas rhizosphere populations revealed that phlD diversity substantially varied between the two soils and that there was a cultivar-specific accumulation of certain phlD genotypes in one soil but not in the other. Furthermore, the three cultivars were tested for their ability to benefit from Pseudomonas inoculants. Interestingly, Arina, which was best protected against Pythium ultimum infection by inoculation with Pseudomonas fluorescens biocontrol strain CHA0, was the cultivar which profited the least from the bacterial inoculant in terms of plant growth promotion in the absence of the pathogen. Knowledge gained of the interactions between wheat cultivars, beneficial Pseudomonads, and soil types allows us to optimize cultivar-soil combinations for the promotion of growth through beneficial Pseudomonads. Additionally, this information can be implemented by breeders into a new and unique breeding strategy for low-input and organic conditions.

Philippe Lemanceau - One of the best experts on this subject based on the ideXlab platform.

  • Pseudomonas fluorescens C7R12 type III secretion system impacts mycorrhization of Medicago truncatula and associated microbial communities
    Mycorrhiza, 2017
    Co-Authors: Amandine Viollet, Philippe Lemanceau, Barbara Pivato, Christophe Mougel, Jean-claude Cleyet-marel, Cécile Gubry-rangin, Sylvie Mazurier
    Abstract:

    Type three secretion systems (T3SSs) mediate cell-to-cell interactions between Gram-negative bacteria and eukaryotes. We hypothesized that fluorescent Pseudomonads harboring T3SS (T3SS+) would be beneficial to arbuscular mycorrhizal symbiosis because non-pathogenic fluorescent Pseudomonads have been previously shown to be much more abundant in mycorrhizal than in non-mycorrhizal roots. We tested this hypothesis by comparing mycorrhization and the associated rhizosphere microbial communities of Medicago truncatula grown in a non-sterile soil inoculated with either the T3SS+ mycorrhiza helper bacterium Pseudomonas fluorescens (C7R12) or a T3SS− mutant of the strain. Results showed that the bacterial secretion system was responsible for the promotion of mycorrhization because root colonization by arbuscular mycorrhizal fungi was not promoted by the T3SS− mutant. The observed T3SS-mediated promotion of mycorrhization was associated with changes in the rhizosphere bacterial communities and the increased occurrence of Claroidoglomeraceae within the intraradical arbuscular mycorrhizal fungi. Furthermore, both Pseudomonad strains promoted the host-free growth of a model arbuscular mycorrhizal fungus in vitro, suggesting that T3SS-mediated promotion of mycorrhization occurs during plant-fungal interactions rather than during the pre-symbiotic phase of fungal growth. Taken together, these data provide evidence for the involvement of T3SS in promoting arbuscular mycorrhization by a model fluorescent Pseudomonad and suggest the implication of interactions between the bacterium and mycorrhizas.

  • Fluorescent Pseudomonads harboring type III secretion genes are enriched in the mycorrhizosphere of Medicago truncatula.
    FEMS microbiology ecology, 2011
    Co-Authors: Amandine Viollet, Philippe Lemanceau, Christophe Mougel, Thérèse Corberand, Agnès Robin, Sylvie Mazurier
    Abstract:

    Type III secretion systems (T3SSs) of Gram-negative bacteria mediate direct interactions with eukaryotic cells. Pseudomonas spp. harboring T3SS genes (T3SS+) were previously shown to be more abundant in the rhizosphere than in bulk soil. To discriminate the contribution of roots and associated arbuscular mycorrhizal fungi (AMF) on the enrichment of T3SS+ fluorescent Pseudomonads in the rhizosphere of Medicago truncatula, their frequency was assessed among Pseudomonads isolated from mycorrhizal and nonmycorrhizal roots and from bulk soil. T3SS genes were identified by PCR targeting a conserved hrcRST DNA fragment. Polymorphism of hrcRST in T3SS+ isolates was assessed by PCR-restriction fragment length polymorphism and sequencing. Genotypic diversity of all Pseudomonads isolated, whether or not harboring T3SS, was described by BOX-PCR. T3SS+ Pseudomonads were significantly more abundant in mycorrhizal than in nonmycorrhizal roots and in bulk soil, and all were shown to belong to the phylogenetic group of Pseudomonas fluorescens on the basis of 16S rRNA gene identity. Four hrcRST genotypes were described; two only included isolates from mycorrhizal roots. T3SS+ and T3SS− Pseudomonads showed different genetic backgrounds as indicated by their different BOX-PCR types. Taken together, these data suggest that T3SSs are implicated in interactions between fluorescent Pseudomonads and AM in medic rhizosphere.

  • Extraction of copper and iron from soil with siderophores of fluorescent Pseudomonads
    2009
    Co-Authors: Matthew James Shirley, Gérard Vansuyt, Eric Bernaud, Philippe Lemanceau
    Abstract:

    Due to the application for more than 100 years of copper to French vineyards to combat fungal diseases of vines copper levels have been reported in vineyard soils up to several hundred milligrams of copper/kg of soil. There are now concerns about the ecotoxicity effects of copper accumulation. One potential way to remediate copper accumulation is phytoextraction. Furthermore, there may be potential to enhance the phytoextraction process by augmenting the process using beneficial bacterial species. Our research has involved investigating the potential to use fluorescent Pseudomonads, a key group of bacteria that produce siderophores (iron-scavenging compounds), to enhance phytoextraction of copper from vineyard soils. Previous work in our group has shown that the siderophores produced by these bacteria are also able to chelate copper. Six fluorescent Pseudomonad strains, producing six different siderophores, were investigated. All six of the siderophores tested were shown to be able to chelate copper, and three of the siderophores (produced by strains NEWT4282, C7R12, and NEM419) were identified as having the highest affinity for copper. In vitro studies with fescue plants grown on agar showed that fescue is able to assimilate copper, either when the copper is provided as copper sulphate or as copper-siderophore chelates. Moreover, significantly more copper was assimilated by fescue in the presence of the NEWT4282 siderophore compared to the copper sulphate control. Finally, experiments are being performed investigating copper assimilation by fescue grown in copper-contaminated vineyard soil, both in laboratory microcosm trials and in a field trial. Early results from the microcosm experiments have shown that inoculation of fescue with either of the strains NEWT4282 or C7R12 leads to an increased concentration of copper in the fescue shoots compared to uninoculated controls, indicating that these strains are able to enhance the phytoextraction process. The field trial remains ongoing. Overall, we have shown: (i) the ability to chelate copper may be a general property of pseudomonas siderophores, (ii) fescue plants are able to assimilate copper from both agar medium and from copper-contaminated soil, and (iii) assimilation of copper from soil can be enhanced by inoculation with siderophore-producing fluorescent Pseudomonad strains. Further experiments will be required to investigate whether there is differential assimilation of copper by pseudomonas-inoculated fescue compared to vines.

  • Effect of ferritin overexpression in tobacco on the structure of bacterial and Pseudomonad communities associated with the roots
    FEMS microbiology ecology, 2006
    Co-Authors: Agnès Robin, Christophe Mougel, Sylvie Mazurier, Séverine Siblot, Gérard Vansuyt, Philippe Lemanceau
    Abstract:

    The genetic structures of total bacterial and Pseudomonad communities were characterized in rhizosphere soil and rhizoplane+root tissues of tobacco wild type and a ferritin overexpressor transgenic line (P6) by a cultivation-independent method using directly extracted DNA at the end of three consecutive plant cultures. The structure of total bacterial communities was characterized by automated ribosomal intergenic spacer analysis (A-RISA), and that of Pseudomonad communities was characterized by PCR-restriction fragment length polymorphism (PCR-RFLP) from DNA amplified with specific primers. The structure of total bacterial communities was significantly modified in the rhizosphere soil by the overaccumulation of iron in the tobacco transgenic P6 line at the first culture, to a lesser extent at the second culture, and not at all at the third culture. No significant difference was recorded between the total communities associated with the roots (rhizoplane+root tissues) of the two plant genotypes in any of the cultures. In contrast, the difference in Pseudomonad structure between the two plant genotypes increased with successive culture at the root level, but was not detected at a significant level in the rhizosphere soil. The impact of iron overaccumulation by the tobacco transgenic P6 line on Pseudomonads supports previous findings on the importance of iron competition among fluorescent Pseudomonads.

  • Effect of ferritin over-expression in tobacco on the structure of bacterial and Pseudomonad communities associated with the roots
    FEMS Microbiology Ecology, 2006
    Co-Authors: Agnès Robin, Christophe Mougel, Sylvie Mazurier, Gérard Vansuyt, Séverine Siblot, Philippe Lemanceau
    Abstract:

    The genetic structures of total bacterial and Pseudomonad communities were characterized in rhizosphere soil and rhizoplane+root tissues of tobacco wild type and a ferritin overexpressor transgenic line (P6) by a cultivation-independent method using directly extracted DNA at the end of three consecutive plant cultures. The structure of total bacterial communities was characterized by automated ribosomal intergenic spacer analysis (A-RISA), and that of Pseudomonad communities was characterized by PCR-restriction fragment length polymorphism (PCR-RFLP) from DNA amplified with specific primers. The structure of total bacterial communities was significantly modified in the rhizosphere soil by the overaccumulation of iron in the tobacco transgenic P6 line at the first culture, to a lesser extent at the second culture, and not at all at the third culture. No significant difference was recorded between the total communities associated with the roots (rhizoplane+root tissues) of the two plant genotypes in any of the cultures. In contrast, the difference in Pseudomonad structure between the two plant genotypes increased with successive culture at the root level, but was not detected at a significant level in the rhizosphere soil. The impact of iron overaccumulation by the tobacco transgenic P6 line on Pseudomonads supports previous findings on the importance of iron competition among fluorescent Pseudomonads.

Sylvie Mazurier - One of the best experts on this subject based on the ideXlab platform.

  • Pseudomonas fluorescens C7R12 type III secretion system impacts mycorrhization of Medicago truncatula and associated microbial communities
    Mycorrhiza, 2017
    Co-Authors: Amandine Viollet, Philippe Lemanceau, Barbara Pivato, Christophe Mougel, Jean-claude Cleyet-marel, Cécile Gubry-rangin, Sylvie Mazurier
    Abstract:

    Type three secretion systems (T3SSs) mediate cell-to-cell interactions between Gram-negative bacteria and eukaryotes. We hypothesized that fluorescent Pseudomonads harboring T3SS (T3SS+) would be beneficial to arbuscular mycorrhizal symbiosis because non-pathogenic fluorescent Pseudomonads have been previously shown to be much more abundant in mycorrhizal than in non-mycorrhizal roots. We tested this hypothesis by comparing mycorrhization and the associated rhizosphere microbial communities of Medicago truncatula grown in a non-sterile soil inoculated with either the T3SS+ mycorrhiza helper bacterium Pseudomonas fluorescens (C7R12) or a T3SS− mutant of the strain. Results showed that the bacterial secretion system was responsible for the promotion of mycorrhization because root colonization by arbuscular mycorrhizal fungi was not promoted by the T3SS− mutant. The observed T3SS-mediated promotion of mycorrhization was associated with changes in the rhizosphere bacterial communities and the increased occurrence of Claroidoglomeraceae within the intraradical arbuscular mycorrhizal fungi. Furthermore, both Pseudomonad strains promoted the host-free growth of a model arbuscular mycorrhizal fungus in vitro, suggesting that T3SS-mediated promotion of mycorrhization occurs during plant-fungal interactions rather than during the pre-symbiotic phase of fungal growth. Taken together, these data provide evidence for the involvement of T3SS in promoting arbuscular mycorrhization by a model fluorescent Pseudomonad and suggest the implication of interactions between the bacterium and mycorrhizas.

  • Fluorescent Pseudomonads harboring type III secretion genes are enriched in the mycorrhizosphere of Medicago truncatula.
    FEMS microbiology ecology, 2011
    Co-Authors: Amandine Viollet, Philippe Lemanceau, Christophe Mougel, Thérèse Corberand, Agnès Robin, Sylvie Mazurier
    Abstract:

    Type III secretion systems (T3SSs) of Gram-negative bacteria mediate direct interactions with eukaryotic cells. Pseudomonas spp. harboring T3SS genes (T3SS+) were previously shown to be more abundant in the rhizosphere than in bulk soil. To discriminate the contribution of roots and associated arbuscular mycorrhizal fungi (AMF) on the enrichment of T3SS+ fluorescent Pseudomonads in the rhizosphere of Medicago truncatula, their frequency was assessed among Pseudomonads isolated from mycorrhizal and nonmycorrhizal roots and from bulk soil. T3SS genes were identified by PCR targeting a conserved hrcRST DNA fragment. Polymorphism of hrcRST in T3SS+ isolates was assessed by PCR-restriction fragment length polymorphism and sequencing. Genotypic diversity of all Pseudomonads isolated, whether or not harboring T3SS, was described by BOX-PCR. T3SS+ Pseudomonads were significantly more abundant in mycorrhizal than in nonmycorrhizal roots and in bulk soil, and all were shown to belong to the phylogenetic group of Pseudomonas fluorescens on the basis of 16S rRNA gene identity. Four hrcRST genotypes were described; two only included isolates from mycorrhizal roots. T3SS+ and T3SS− Pseudomonads showed different genetic backgrounds as indicated by their different BOX-PCR types. Taken together, these data suggest that T3SSs are implicated in interactions between fluorescent Pseudomonads and AM in medic rhizosphere.

  • Effect of ferritin overexpression in tobacco on the structure of bacterial and Pseudomonad communities associated with the roots
    FEMS microbiology ecology, 2006
    Co-Authors: Agnès Robin, Christophe Mougel, Sylvie Mazurier, Séverine Siblot, Gérard Vansuyt, Philippe Lemanceau
    Abstract:

    The genetic structures of total bacterial and Pseudomonad communities were characterized in rhizosphere soil and rhizoplane+root tissues of tobacco wild type and a ferritin overexpressor transgenic line (P6) by a cultivation-independent method using directly extracted DNA at the end of three consecutive plant cultures. The structure of total bacterial communities was characterized by automated ribosomal intergenic spacer analysis (A-RISA), and that of Pseudomonad communities was characterized by PCR-restriction fragment length polymorphism (PCR-RFLP) from DNA amplified with specific primers. The structure of total bacterial communities was significantly modified in the rhizosphere soil by the overaccumulation of iron in the tobacco transgenic P6 line at the first culture, to a lesser extent at the second culture, and not at all at the third culture. No significant difference was recorded between the total communities associated with the roots (rhizoplane+root tissues) of the two plant genotypes in any of the cultures. In contrast, the difference in Pseudomonad structure between the two plant genotypes increased with successive culture at the root level, but was not detected at a significant level in the rhizosphere soil. The impact of iron overaccumulation by the tobacco transgenic P6 line on Pseudomonads supports previous findings on the importance of iron competition among fluorescent Pseudomonads.

  • Effect of ferritin over-expression in tobacco on the structure of bacterial and Pseudomonad communities associated with the roots
    FEMS Microbiology Ecology, 2006
    Co-Authors: Agnès Robin, Christophe Mougel, Sylvie Mazurier, Gérard Vansuyt, Séverine Siblot, Philippe Lemanceau
    Abstract:

    The genetic structures of total bacterial and Pseudomonad communities were characterized in rhizosphere soil and rhizoplane+root tissues of tobacco wild type and a ferritin overexpressor transgenic line (P6) by a cultivation-independent method using directly extracted DNA at the end of three consecutive plant cultures. The structure of total bacterial communities was characterized by automated ribosomal intergenic spacer analysis (A-RISA), and that of Pseudomonad communities was characterized by PCR-restriction fragment length polymorphism (PCR-RFLP) from DNA amplified with specific primers. The structure of total bacterial communities was significantly modified in the rhizosphere soil by the overaccumulation of iron in the tobacco transgenic P6 line at the first culture, to a lesser extent at the second culture, and not at all at the third culture. No significant difference was recorded between the total communities associated with the roots (rhizoplane+root tissues) of the two plant genotypes in any of the cultures. In contrast, the difference in Pseudomonad structure between the two plant genotypes increased with successive culture at the root level, but was not detected at a significant level in the rhizosphere soil. The impact of iron overaccumulation by the tobacco transgenic P6 line on Pseudomonads supports previous findings on the importance of iron competition among fluorescent Pseudomonads.

Yvan Moënne-loccoz - One of the best experts on this subject based on the ideXlab platform.

  • Development of a 16S rRNA microarray approach for the monitoring of rhizosphere Pseudomonas populations associated with the decline of take-all disease of wheat.
    Soil Biology and Biochemistry, 2008
    Co-Authors: Hervé Sanguin, L. Kroneisen, Kevin Gazengel, M. Kyselková, Benoit Remenant, Claire Prigent-combaret, G.l. Grundmann, Alain Sarniguet, Yvan Moënne-loccoz
    Abstract:

    So far, the analysis of microbial populations associated with wheat monocropping-induced decline of take-all disease (Gaeumannomyces graminis var. tritici) has focused mainly on culturable biocontrol Pseudomonads. The objective of this study was to develop a taxonomic rrs (16S rRNA gene) microarray to assess the changes in Pseudomonas populations taking place during take-all decline. The microarray contains 12 probes for five Pseudomonas phylogenetic clusters chosen because they include well-known plant-beneficial Pseudomonads. Four of the clusters are within the ‘Pseudomonas fluorescens’ species complex. PCR primers were selected to target these five clusters, and they were validated using 53 Pseudomonads belonging or not to these clusters. Microarray analysis of the Pseudomonads enabled discrimination between strains from several Pseudomonas clusters. Rhizosphere samples were collected from field plots grown with wheat for 1 (low level of take-all disease), 5 (high level of disease) or 10 years (low level of disease, suppressiveness reached). Microarray data could distinguish Pseudomonas populations from some of the wheat plants grown in the same plot. When comparing treatments, there was a difference between years 1 and 10. Cloning–sequencing of rrs enabled to define more precisely this difference by identifying two major Pseudomonas populations, one associated with year 1 and the other with year 10 (disease suppressiveness), which represent new clades within the ‘P. fluorescens’ complex. These populations may be useful as soil quality indicators. In conclusion, the combination of microarray and cloning–sequencing approaches highlighted changes in the prevalence of two major Pseudomonas populations, giving new insights on the dynamics of root-associated Pseudomonads during take-all decline

  • Multilocus sequence analysis of biocontrol fluorescent Pseudomonas spp. producing the antifungal compound 2,4-diacetylphloroglucinol
    Environmental Microbiology, 2007
    Co-Authors: Michele Frapolli, Geneviève Défago, Yvan Moënne-loccoz
    Abstract:

    The genetic and evolutionary relationship among 2,4-diacetylphloroglucinol (Phl)-producing Pseudomonads that protect plants from soil-borne pathogens were investigated by multilocus sequence typing. A total of 65 Pseudomonads consisting of 58 Phl-positive biocontrol strains of worldwide origin and seven Phl-negative representatives of characterized Pseudomonas species were compared using 10 housekeeping genes (i.e. rrs, dsbA, gyrB, rpoD, fdxA, recA, rpoB, fusA, rpsL and rpsG). Multilocus sequence typing differentiated 51 strains among 58 Phl-positive Pseudomonads and proved to be as discriminative as enterobacterial repetitive intergenic consensus polymerase chain reaction profiling. As phylogenetic trees inferred from each locus were rather incongruent with one another, we derived the topology from all concatenated loci, which led to the identification of six main groups of Phl-producing Pseudomonas spp. Taxonomically, these groups could correspond to at least six different species. Linkage disequilibrium analysis pointed to a rather clonal structure, even when the analysis was restricted to Phl-producing Pseudomonads from a same geographic location or a same phylogenetic group. Intragenic recombination was evidenced for gyrB, rpoD and fdxA, but was shown to be a weaker force than mutation in the origin of intragenetic diversity. This is the first multilocus assessment of the phylogeny and population structure of an ecologically important bacterial group involved in plant disease suppression.

  • Genetic diversity and biocontrol potential of fluorescent Pseudomonads producing phloroglucinols and hydrogen cyanide from Swiss soils naturally suppressive of conducive to Thielaviopsis basicola-mediated black root rot of tabacco
    FEMS Microbiology Ecology, 2006
    Co-Authors: Yvan Moënne-loccoz, Alban Ramette, Geneviève Défago
    Abstract:

    Pseudomonas populations producing the biocontrol compounds 2,4-diacetylphloroglucinol (Phl) and hydrogen cyanide (HCN) were found in the rhizosphere of tobacco both in Swiss soils suppressive to Thielaviopsis basicola and in their conducive counterparts. In this study, a collection of Phl1 HCN1 Pseudomonas isolates from two suppressive and two conducive soils were used to assess whether suppressiveness could be linked to soil-specific properties of individual Pseudomonads. The isolates were compared based on restriction analysis of the biocontrol genes phlD and hcnBC, enterobacterial repetitive intergenic consensus (ERIC)- PCR profiling and their biocontrol ability. Restriction analyses of phlD and hcnBC yielded very concordant relationships between the strains, and suggested significant population differentiation occurring at the soil level, regardless of soil suppressiveness status. This was corroborated by high strain diversity (ERICPCR) within each of the four soils and among isolates harboring the same phlD or hcnBC alleles. No correlation was found between the origin of the isolates and their biocontrol activity in vitro and in planta. Significant differences in T. basicola inhibition were however evidenced between the isolates when they were grouped according to their biocontrol alleles. Moreover, two main Pseudomonas lineages differing by the capacity to produce pyoluteorin were evidenced in the collection. Thus, Phl1 HCN1 Pseudomonads from suppressive soils were not markedly different from those from nearby conducive soils. Therefore, as far as biocontrol Pseudomonads are concerned, this work yields the hypothesis that the suppressiveness of Swiss soils may rely on the differential effects of environmental factors on the expression of key biocontrol genes in Pseudomonads rather than differences in population structure of biocontrol Pseudomonas subcommunities or the biocontrol potential of individual Phl1 HCN1 Pseudomonad strains.

  • Life as a Biocontrol Pseudomonad
    Pseudomonas, 2004
    Co-Authors: Yvan Moënne-loccoz, Geneviève Défago
    Abstract:

    Many Pseudomonas strains can benefit plants directly, by promoting plant growth and health, and/or indirectly through inhibition of, or competition with pathogens, parasites, or plant competitors21, 32, 39, 43,60,79. Not all Pseudomonads have biocontrol capacities, and among those that do certain display several different biocontrol mechanisms. Current Pseudomonas taxonomy is not satisfactory and requires extensive revision9, 86, but from the existing knowledge it appears that biocontrol capacities are rather straindependent than species-dependent. The significance of biocontrol Pseudomonads for plant protection is exemplified by their contribution to disease-suppressiveness of soils62, 65, 112. This chapter provides an overview of the ecological particularities of biocontrol Pseudomonads, as well as a review of interaction mechanisms with phytopathogens, the plant, and non-target soil microbiota.

Geneviève Défago - One of the best experts on this subject based on the ideXlab platform.

  • Interplay between wheat cultivars, biocontrol Pseudomonads, and soil.
    Applied and environmental microbiology, 2010
    Co-Authors: Joana Beatrice Meyer, Geneviève Défago, Michele Frapolli, Christoph Keel, Matthias P. Lutz, Maria Péchy-tarr, Laurène Rochat, Monika Maurhofer
    Abstract:

    There is a significant potential to improve the plant-beneficial effects of root-colonizing Pseudomonads by breeding wheat genotypes with a greater capacity to sustain interactions with these bacteria. However, the interaction between Pseudomonads and crop plants at the cultivar level, as well as the conditions which favor the accumulation of beneficial microorganisms in the wheat rhizosphere, is largely unknown. Therefore, we characterized the three Swiss winter wheat (Triticum aestivum) cultivars Arina, Zinal, and Cimetta for their ability to accumulate naturally occurring plant-beneficial Pseudomonads in the rhizosphere. Cultivar performance was measured also by the ability to select for specific genotypes of 2,4-diacetylphloroglucinol (DAPG) producers in two different soils. Cultivar-specific differences were found; however, these were strongly influenced by the soil type. Denaturing gradient gel electrophoresis (DGGE) analysis of fragments of the DAPG biosynthetic gene phlD amplified from natural Pseudomonas rhizosphere populations revealed that phlD diversity substantially varied between the two soils and that there was a cultivar-specific accumulation of certain phlD genotypes in one soil but not in the other. Furthermore, the three cultivars were tested for their ability to benefit from Pseudomonas inoculants. Interestingly, Arina, which was best protected against Pythium ultimum infection by inoculation with Pseudomonas fluorescens biocontrol strain CHA0, was the cultivar which profited the least from the bacterial inoculant in terms of plant growth promotion in the absence of the pathogen. Knowledge gained of the interactions between wheat cultivars, beneficial Pseudomonads, and soil types allows us to optimize cultivar-soil combinations for the promotion of growth through beneficial Pseudomonads. Additionally, this information can be implemented by breeders into a new and unique breeding strategy for low-input and organic conditions.

  • Multilocus sequence analysis of biocontrol fluorescent Pseudomonas spp. producing the antifungal compound 2,4-diacetylphloroglucinol
    Environmental Microbiology, 2007
    Co-Authors: Michele Frapolli, Geneviève Défago, Yvan Moënne-loccoz
    Abstract:

    The genetic and evolutionary relationship among 2,4-diacetylphloroglucinol (Phl)-producing Pseudomonads that protect plants from soil-borne pathogens were investigated by multilocus sequence typing. A total of 65 Pseudomonads consisting of 58 Phl-positive biocontrol strains of worldwide origin and seven Phl-negative representatives of characterized Pseudomonas species were compared using 10 housekeeping genes (i.e. rrs, dsbA, gyrB, rpoD, fdxA, recA, rpoB, fusA, rpsL and rpsG). Multilocus sequence typing differentiated 51 strains among 58 Phl-positive Pseudomonads and proved to be as discriminative as enterobacterial repetitive intergenic consensus polymerase chain reaction profiling. As phylogenetic trees inferred from each locus were rather incongruent with one another, we derived the topology from all concatenated loci, which led to the identification of six main groups of Phl-producing Pseudomonas spp. Taxonomically, these groups could correspond to at least six different species. Linkage disequilibrium analysis pointed to a rather clonal structure, even when the analysis was restricted to Phl-producing Pseudomonads from a same geographic location or a same phylogenetic group. Intragenic recombination was evidenced for gyrB, rpoD and fdxA, but was shown to be a weaker force than mutation in the origin of intragenetic diversity. This is the first multilocus assessment of the phylogeny and population structure of an ecologically important bacterial group involved in plant disease suppression.

  • Genetic diversity and biocontrol potential of fluorescent Pseudomonads producing phloroglucinols and hydrogen cyanide from Swiss soils naturally suppressive of conducive to Thielaviopsis basicola-mediated black root rot of tabacco
    FEMS Microbiology Ecology, 2006
    Co-Authors: Yvan Moënne-loccoz, Alban Ramette, Geneviève Défago
    Abstract:

    Pseudomonas populations producing the biocontrol compounds 2,4-diacetylphloroglucinol (Phl) and hydrogen cyanide (HCN) were found in the rhizosphere of tobacco both in Swiss soils suppressive to Thielaviopsis basicola and in their conducive counterparts. In this study, a collection of Phl1 HCN1 Pseudomonas isolates from two suppressive and two conducive soils were used to assess whether suppressiveness could be linked to soil-specific properties of individual Pseudomonads. The isolates were compared based on restriction analysis of the biocontrol genes phlD and hcnBC, enterobacterial repetitive intergenic consensus (ERIC)- PCR profiling and their biocontrol ability. Restriction analyses of phlD and hcnBC yielded very concordant relationships between the strains, and suggested significant population differentiation occurring at the soil level, regardless of soil suppressiveness status. This was corroborated by high strain diversity (ERICPCR) within each of the four soils and among isolates harboring the same phlD or hcnBC alleles. No correlation was found between the origin of the isolates and their biocontrol activity in vitro and in planta. Significant differences in T. basicola inhibition were however evidenced between the isolates when they were grouped according to their biocontrol alleles. Moreover, two main Pseudomonas lineages differing by the capacity to produce pyoluteorin were evidenced in the collection. Thus, Phl1 HCN1 Pseudomonads from suppressive soils were not markedly different from those from nearby conducive soils. Therefore, as far as biocontrol Pseudomonads are concerned, this work yields the hypothesis that the suppressiveness of Swiss soils may rely on the differential effects of environmental factors on the expression of key biocontrol genes in Pseudomonads rather than differences in population structure of biocontrol Pseudomonas subcommunities or the biocontrol potential of individual Phl1 HCN1 Pseudomonad strains.

  • Life as a Biocontrol Pseudomonad
    Pseudomonas, 2004
    Co-Authors: Yvan Moënne-loccoz, Geneviève Défago
    Abstract:

    Many Pseudomonas strains can benefit plants directly, by promoting plant growth and health, and/or indirectly through inhibition of, or competition with pathogens, parasites, or plant competitors21, 32, 39, 43,60,79. Not all Pseudomonads have biocontrol capacities, and among those that do certain display several different biocontrol mechanisms. Current Pseudomonas taxonomy is not satisfactory and requires extensive revision9, 86, but from the existing knowledge it appears that biocontrol capacities are rather straindependent than species-dependent. The significance of biocontrol Pseudomonads for plant protection is exemplified by their contribution to disease-suppressiveness of soils62, 65, 112. This chapter provides an overview of the ecological particularities of biocontrol Pseudomonads, as well as a review of interaction mechanisms with phytopathogens, the plant, and non-target soil microbiota.