Effects of Soil Matric Potential and Cell Motility on Wheat Root Colonization by Fluorescent Pseudomonads Suppressive to Take-All

Howie, William J.

doi:10.1094/phyto-77-286

Cited by 161 publications

(79 citation statements)

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“…These observations confirm our initial hypothesis suggesting that the selective advantage given to the wild-type strain C7R12 by the nitrate reductase would be expressed under conditions of lower aeration. Several studies have stressed the impact of matric potential on soilborne fluorescent pseudomonads (3,10,11,27). However, to our knowledge, the present study is the first to demonstrate the implication of an enzyme in the bacterial adaptation to variations of matric potential.…”

Section: Construction Of the Narmentioning

confidence: 46%

Involvement of Nitrate Reductase and Pyoverdine in Competitiveness of Pseudomonas fluorescens Strain C7R12 in Soil

Mirleau

Philippot

Corberand

et al. 2001

Appl Environ Microbiol

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Involvement of nitrate reductase and pyoverdine in the competitiveness of the biocontrol strain Pseudomonas fluorescens C7R12 was determined, under gnotobiotic conditions, in two soil compartments (bulk and rhizosphere soil), with the soil being kept at two different values of matric potential (؊1 and ؊10 kPa). Three mutants affected in the synthesis of either the nitrate reductase (Nar ؊ ), the pyoverdine (Pvd ؊ ), or both (Nar ؊ Pvd ؊ ) were used. The Nar ؊ and Nar ؊ Pvd ؊ mutants were obtained by site-directed mutagenesis of the wildtype strain and of the Pvd ؊ mutant, respectively. The selective advantage given by nitrate reductase and pyoverdine to the wild-type strain was assessed by measuring the dynamic of each mutant-to-total-inoculant (wild-type strain plus mutant) ratio. All three mutants showed a lower competitiveness than the wild-type strain, indicating that both nitrate reductase and pyoverdine are involved in the fitness of P. fluorescens C7R12. The double mutant presented the lowest competitiveness. Overall, the competitive advantages given to C7R12 by nitrate reductase and pyoverdine were similar. However, the selective advantage given by nitrate reductase was more strongly expressed under conditions of lower aeration (؊1 kPa). In contrast, the selective advantage given by nitrate reductase and pyoverdine did not differ in bulk and rhizosphere soil, indicating that these bacterial traits are not specifically involved in the rhizosphere competence but rather in the saprophytic ability of C7R12 in soil environments.

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Section: Construction Of the Narmentioning

confidence: 46%

Involvement of Nitrate Reductase and Pyoverdine in Competitiveness of Pseudomonas fluorescens Strain C7R12 in Soil

Mirleau

Philippot

Corberand

et al. 2001

Appl Environ Microbiol

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“…Among nonpathogenic plant-associated microbes, swimming motility increased epiphytic fitness of leafcolonizing strains of P. syringae (27), while nonmotile strains of the free-living nitrogen-fixing bacterium Azospirillum brasilense and of a plant growth-promoting P. fluorescens strain were much less able to colonize host roots (19,57). Conversely, nonmotile P. fluorescens biocontrol strains colonized wheat and pea roots as well as wild-type motile strains (9,33). Some, but not all, data suggest that motility increases competitiveness of Rhizobium strains under field conditions (5,13,38).…”

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confidence: 99%

Ralstonia solanacearum Needs Motility for Invasive Virulence on Tomato

2001

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Ralstonia solanacearum, a widely distributed and economically important plant pathogen, invades the roots of diverse plant hosts from the soil and aggressively colonizes the xylem vessels, causing a lethal wilting known as bacterial wilt disease. By examining bacteria from the xylem vessels of infected plants, we found that R. solanacearum is essentially nonmotile in planta, although it can be highly motile in culture. To determine the role of pathogen motility in this disease, we cloned, characterized, and mutated two genes in the R. solanacearum flagellar biosynthetic pathway. The genes for flagellin, the subunit of the flagellar filament (fliC), and for the flagellar motor switch protein (fliM) were isolated based on their resemblance to these proteins in other bacteria. As is typical for flagellins, the predicted FliC protein had well-conserved N-and C-terminal regions, separated by a divergent central domain. The predicted R. solanacearum FliM closely resembled motor switch proteins from other proteobacteria. Chromosomal mutants lacking fliC or fliM were created by replacing the genes with marked interrupted constructs. Since fliM is embedded in the fliLMNOPQR operon, the aphA cassette was used to make a nonpolar fliM mutation. Both mutants were completely nonmotile on soft agar plates, in minimal broth, and in tomato plants. The fliC mutant lacked flagella altogether; moreover, shearedcell protein preparations from the fliC mutant lacked a 30-kDa band corresponding to flagellin. The fliM mutant was usually aflagellate, but about 10% of cells had abnormal truncated flagella. In a biologically representative soil-soak inoculation virulence assay, both nonmotile mutants were significantly reduced in the ability to cause disease on tomato plants. However, the fliC mutant had wild-type virulence when it was inoculated directly onto cut tomato petioles, an inoculation method that did not require bacteria to enter the intact host from the soil. These results suggest that swimming motility makes its most important contribution to bacterial wilt virulence in the early stages of host plant invasion and colonization.

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“…However, little is known about the role of this complex behavior in microbial ecology (23). Although the existence of chemotaxis in plant-associated bacteria is well documented (see, for example, references 5, 10, 14, and 24 (20,27) (18).…”

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confidence: 99%

Requirement for chemotaxis in pathogenicity of Agrobacterium tumefaciens on roots of soil-grown pea plants

Hawes

Smith

1989

J Bacteriol

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Agrobacterium tumefaciens Tn5 mutants deficient in chemotaxis to root exudates were used to study the significance of chemotaxis in crown gall pathogenesis. Mutants deficient in motility and in chemotaxis were fully virulent when inoculated by direct immersion in inoculum, followed by growth for 2 weeks in moist growth pouches. Ability of mutant bacteria to move through soil to infect roots was tested by planting wounded seedlings into air-dried soil or sand that had been infested with inoculum. Mutant bacteria were almost as virulent as the parent on plants grown in sand but were avirulent on soil-grown plants.

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Effects of Soil Matric Potential and Cell Motility on Wheat Root Colonization by Fluorescent Pseudomonads Suppressive to Take-All

Cited by 161 publications

References 0 publications

Involvement of Nitrate Reductase and Pyoverdine in Competitiveness of Pseudomonas fluorescens Strain C7R12 in Soil

Involvement of Nitrate Reductase and Pyoverdine in Competitiveness of Pseudomonas fluorescens Strain C7R12 in Soil

Ralstonia solanacearum Needs Motility for Invasive Virulence on Tomato

Requirement for chemotaxis in pathogenicity of Agrobacterium tumefaciens on roots of soil-grown pea plants

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