The establishment of an introduced community of fluorescent pseudomonads in the soil and in the rhizosphere is affected by the soil type

International audienc

Comparison of the survival kinetics of a strain of pseudomonas putida in the rhizosphere of two different plant species

National audienc

Role of antibiotic-producing pseudomonads in natural soil suppressiveness to Fusarium wilt

National audienc

The composition of fluorescent pseudomonad populations associated with roots is influenced by plant and soil type

International audienc

The composition of fluorescent pseudomonad populations associated with roots is influenced by plant and soil type

International audienc

Antibiosis as a possible mechanism of soil suppressiveness to Fusarium wilts

International audienc

Pseudomonas lini sp. nov., a novel species from bulk and rhizospheric soils

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Rôle de la nitrate réductase et de la pyoverdine dans la compétence tellurique et rhizosphérique de la souche Pseudomonas fluorescens C7R12

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Arbuscular mycorrhizae influence the occurence of soil fluorescent pseudomonads harbouring type III secretion systems

International audienceType III secretion systems (T3SS) of pathogenic and symbiotic Gram negative bacteria allow direct interactions with eukaryotic cells. Saprophytic fluorescent Pseudomonas spp. harbouring T3SS genes (T3SS+) have been more frequently encountered in the rhizosphere than in bulk soil, which suggests a possible interaction between these bacteria and rhizospheric eukaryotes.Our objectives were to compare, (i) the effect of mycorrhizal and of non-mycorrhizal roots of Medicago truncatula on the occurrence and diversity of T3SS+ fluorescent Pseudomonas spp.and (ii) the diversity of T3SS+and T3SS- bacterial genotypes.Fluorescent pseudomonads from (i) the rhizosphere of mycorrhizal roots of M. truncatula Jemalong J5 (wild-type, Myc+ Nod+) and TRV48 (mutant Myc+ Nod-), (ii) the rhizosphere of non-mycorrhizal roots of TRV45 (mutant Myc- Nod-), and (iii) the corresponding bulk soil were isolated. Pseudomonas spp. strains harbouring T3SS genes were identified by PCR targeting a conserved hrcRST DNA fragment. Genotypic diversity of fluorescent pseudomonads has been described by a whole cell rep-PCR fingerprinting method (BOX-PCR) and 16S rRNA sequencing. For T3SS+ strains the polymorphism of hrcRST has been assessed by PCR-RFLP and sequencing.The occurrence of T3SS+ fluorescent pseudomonads was significantly higher in the rhizosphere of mycorrhizal (J5 and TRV48) than in that of non-mycorrhizal roots (TRV45) or in the bulk soil. Four distinct hrcRST genotypes were described, two of which were specifically described for strains associated with mycorrhizal roots. Compared to hrcRST negative fluorescent pseudomonads, T3SS+ strains displayed specific BOX-PCR genotypes that were all ascribed to the phylogenetic group of P. fluorescens on the basis of 16S rRNA gene identity.Mycorrhizal roots of Medicago truncatula clearly influence the population structure of root associated fluorescent pseudomonads in a different way than non-mycorrhizal roots. The occurrence of particular genotypes of fluorescent Pseudomonas spp. harbouring T3SS genes was highly increased in the rhizosphere of mycorrhizal roots suggesting that T3SS might be implicated in cellular interactions between fluorescent pseudomonads and arbuscular mycorrhizae

Fluorescent pseudomonads harboring type III secretion genes are enriched in the mycorrhizosphere of Medicago truncatula

International audienceType 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