Impact of wild‐type and genetically modified<i>Pseudomonas fluorescens</i>on soil enzyme activities and microbial population structure in the rhizosphere of pea

Naseby, D.C.; Lynch, J. M.

doi:10.1046/j.1365-294x.1998.00367.x

Cited by 64 publications

(31 citation statements)

References 38 publications

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“…Pseudomonas spp. can colonize the roots of a wide range of plants (Simons et al, 1996;Naseby & Lynch, 1998;Villacieros et al, 2003), being one of the best root colonizers, and are used as a model in root-colonization studies (Bloemberg et al, 2000; Chin-a-Woeng et al, 2000). The rhizosphere is a complex environment that supports a large and metabolically active microbial population, several orders of magnitude higher than the non-rhizospheric soil.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Pseudomonas fluorescens F113 genes implicated in flagellar filament synthesis and their role in competitive root colonization

et al. 2004

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The ability of plant-associated micro-organisms to colonize and compete in the rhizosphere is specially relevant for the biotechnological application of micro-organisms as inoculants. Pseudomonads are one of the best root colonizers and they are widely used in plant-pathogen biocontrol and in soil bioremediation. This study analyses the motility mechanism of the well-known biocontrol strain Pseudomonas fluorescens F113. A 6?5 kb region involved in the flagellar filament synthesis, containing the fliC, flaG, fliD, fliS, fliT and fleQ genes and part of the fleS gene, was sequenced and mutants in this region were made. Several non-motile mutants affected in the fliC, fliS and fleQ genes, and a fliT mutant with reduced motility properties, were obtained. These mutants were completely displaced from the root tip when competing with the wild-type F113 strain, indicating that the wild-type motility properties are necessary for competitive root colonization. A mutant affected in the flaG gene had longer flagella, but the same motility and colonization properties as the wild-type. However, in rich medium or in the absence of iron limitation, it showed a higher motility, suggesting the possibility of improving competitive root colonization by manipulating the motility processes. INTRODUCTIONThe study of rhizosphere colonization by micro-organisms is crucial for the efficient application of bacteria as inoculants, both in agricultural and in environmental biotechnology processes. Pseudomonas spp. can colonize the roots of a wide range of plants (Simons et al., 1996;Naseby & Lynch, 1998;Villacieros et al., 2003), being one of the best root colonizers, and are used as a model in root-colonization studies (Bloemberg et al., 2000; Chin-a-Woeng et al., 2000). The rhizosphere is a complex environment that supports a large and metabolically active microbial population, several orders of magnitude higher than the non-rhizospheric soil. Many bacterial genes and traits have been shown to be involved in plant-root colonization (Lugtenberg & Dekkers, 1999;Rainey, 1999;Lugtenberg et al., 2001). However, not only colonization but also the pseudomonads' ability to compete with the indigenous microbial population are essential to improve their biotechnological applications in the rhizosphere environment.The soil-borne fluorescent pseudomonads are used as biocontrol inoculants because of their ability to produce some antifungal metabolites (Dowling & O'Gara, 1994;Walsh et al., 2001). Other applications of pseudomonads include soil biofertilization and rhizoremediation (Ramos et al., 1991; Brazil et al., 1995; Höflich et al., 1995;Yee et al., 1998).The strain Pseudomonas fluorescens F113 was isolated from the sugarbeet rhizosphere and it is used as a biocontrol agent against the fungal pathogen Pythium ultimum, which causes damping-off disease in sugarbeet seedlings. The biocontrol abilities of this strain are due mainly to the production of the antifungal metabolite DAPG (2,4-diacetylphloroglucinol) (Shanahan et al., 1992). P. fluorescens ...

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Section: Introductionmentioning

confidence: 99%

Analysis of Pseudomonas fluorescens F113 genes implicated in flagellar filament synthesis and their role in competitive root colonization

et al. 2004

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“…Indirect evidence of perturbations caused by bacterial inoculants on the indigenous bacterial community of the rhizosphere has been obtained by studying community-level catabolic profiles on BIOLOG plates, microbial enzymatic activities, profiles of fatty acid methyl esters extracted from the rhizosphere, and/or the distribution of r/K strategists on plates (10,11,34,37,46). The impact of biocontrol pseudomonads on the diversity of the bacterial community has been investigated at the level of the genus and/or species (26,37), and it can be expected that this type of work will benefit from current developments in molecular, culture-independent approaches (25,38).…”

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confidence: 99%

Impact of 2,4-Diacetylphloroglucinol-Producing Biocontrol Strain Pseudomonas fluorescens F113 on Intraspecific Diversity of Resident Culturable Fluorescent Pseudomonads Associated with the Roots of Field-Grown Sugar Beet Seedlings

Moënne‐Loccoz

Tichy²,

O'Donnell

et al. 2001

Appl Environ Microbiol

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The impact of the 2,4-diacetylphloroglucinol-producing biocontrol agent Pseudomonas fluorescens F113Rif on the diversity of the resident community of culturable fluorescent pseudomonads associated with the roots of field-grown sugar beet seedlings was evaluated. At 19 days after sowing, the seed inoculant F113Rif had replaced some of the resident culturable fluorescent pseudomonads at the rhizoplane but had no effect on the number of these bacteria in the rhizosphere. A total of 498 isolates of resident fluorescent pseudomonads were obtained and characterized by molecular means at the level of broad phylogenetic groups (by amplified ribosomal DNA restriction analysis) and at the strain level (with random amplified polymorphic DNA markers) as well as phenotypically (55 physiological tests). The introduced pseudomonad induced a major shift in the composition of the resident culturable fluorescent Pseudomonas community, as the percentage of rhizoplane isolates capable of growing on three carbon substrates (erythritol, adonitol, and L-tryptophan) not assimilated by the inoculant was increased from less than 10% to more than 40%. However, the pseudomonads selected did not display enhanced resistance to 2,4-diacetylphloroglucinol. The shift in the resident populations, which was spatially limited to the surface of the root (i.e., the rhizoplane), took place without affecting the relative proportions of phylogenetic groups or the high level of strain diversity of the resident culturable fluorescent Pseudomonas community. These results suggest that the root-associated Pseudomonas community of sugar beet seedlings is resilient to the perturbation that may be caused by a taxonomically related inoculant.

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“…The persistence of rhizobia bearing genetic modifications has been related to many factors mainly regarding soil type, presence of host legume and competing co-specific strains (Hagen et al, 1997). In relation to lactose, microcosm soil trials performed in pea rhizospheres with Pseudomonas fluorescens carrying lacZY, during a 21 days incubation, showed that the substrate could enhance the GMM recovery by 0.3 of a log unit (Naseby and Lynch, 1998).…”

Section: Discussionmentioning

confidence: 99%

Long term evaluation of field-released genetically modified rhizobia

Corich

Vendramin

Vian

et al. 2007

Environ. Biosafety Res.

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This is the report of the first open field release of genetically modified microorganisms (GMMs) in Italy. It covers ten years of monitoring, and follows in-field GMM dynamics from strain release to disappearance below detection limits, as well as assessment of impact on resident microorganisms. The bacteria released belong to the nitrogen fixing legume endosymbiont Rhizobium leguminosarum bv. viciae, and were engineered with non-agronomically-proficient traits, in order to assess their behavior and fate without GMM-specific positive feedback from the plant. A DNA cassette containing mercury resistance and ß-galactosidase genes was introduced in either plasmid-borne or chromosomally integrated versions, in order to test the resulting strain stability. A synthetic promoter was used to drive the lacZ gene, conferring high catabolic activity to the GMM. Two different wild-type Rhizobium backgrounds were tested, comparing a non-indigenous vs. an indigenous, highly competitive strain. The latter had much greater persistence, since it was able to survive and establish at technically detectable levels for over four years after release. Selection factors, such as reiterated presence of the plant host, or lactose substrate supply, enhanced long-term survival to different extents. The lactose treatment showed that even a single trophic supplementation can surpass the benefits of symbiotic interaction for a period of several years. Concerning impact, the GMMs did not alter substantially the other soil community general microbiota. However, there were some significant differences in microbiota as a consequence of the Rhizobium inoculation. This effect was observed with either the WT or GMM, and was more evident in the release of the indigenous Rhizobium. Moreover, as the indigenous GMM had its parental, dominant wild-type in the same soil, it was possible to evaluate to what extent the GMM version could result in parent displacement ("self-impact"), and how much the two rhizobia would additively contribute to nodulation.

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Impact of wild‐type and genetically modifiedPseudomonas fluorescenson soil enzyme activities and microbial population structure in the rhizosphere of pea

Cited by 64 publications

References 38 publications

Analysis of Pseudomonas fluorescens F113 genes implicated in flagellar filament synthesis and their role in competitive root colonization

Analysis of Pseudomonas fluorescens F113 genes implicated in flagellar filament synthesis and their role in competitive root colonization

Impact of 2,4-Diacetylphloroglucinol-Producing Biocontrol Strain Pseudomonas fluorescens F113 on Intraspecific Diversity of Resident Culturable Fluorescent Pseudomonads Associated with the Roots of Field-Grown Sugar Beet Seedlings

Long term evaluation of field-released genetically modified rhizobia

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