title: Fluorescent pseudomonads harboring type III secretion genes are enriched in the mycorrhizosphere of Medicago truncatula.
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.
authors.affiliation: INRA, Université de Bourgogne, UMR 1229 Microbiologie du Sol et de l'Environnement, CMSE, Dijon, France.
authors.forename: Amandine
authors.initials: A
authors.lastname: Viollet
authors.forename: Thérèse
authors.initials: T
authors.lastname: Corberand
authors.forename: Christophe
authors.initials: C
authors.lastname: Mougel
authors.forename: Agnès
authors.initials: A
authors.lastname: Robin
authors.forename: Philippe
authors.initials: P
authors.lastname: Lemanceau
authors.forename: Sylvie
authors.initials: S
authors.lastname: Mazurier
mesh_terms: D058947:Bacterial Secretion Systems / Q000235:genetics*; D014644:Genetic Variation; D005838:Genotype; D046913:Medicago truncatula / Q000235:genetics / Q000254:growth & development / Q000382:microbiology*; D008969:Molecular Sequence Data; D038821:Mycorrhizae; D010802:Phylogeny; D018517:Plant Roots / Q000382:microbiology*; D011549:Pseudomonas / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D011551:Pseudomonas fluorescens / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D058441:Rhizosphere; D012988:Soil Microbiology
chemical_list: D058947:Bacterial Secretion Systems; D012336:RNA, Ribosomal, 16S