Diversity of N-acyl homoserine lactone-producing and -degrading bacteria in soil and tobacco rhizosphere.
Résumé
In Gram-negative bacteria,quorum-sensing (QS) communication is mostly mediated by N-acyl homoserine lactones (N-AHSL). The diversity of bacterial populations that produce or inactivate the N-AHSL signal in soil and tobacco rhizosphere was investigated by restriction fragment length polymorphism (RFLP) analysis of amplified 16S DNA and DNA sequencing. Such analysis indicated the occurrence of N-AHSL-producing strains among the α-,β- and γ-proteobacteria,including genera known to produce N-AHSL (Rhizobium,Sinorhizobium and Pseudomonas) and novel genera with no previously identified N-AHSL-producing isolates (Variovorax,Sphingomonas and Massilia). The diversity of N-AHSL signals was also investigated in relation to the genetic diversity of the isolates. However,N-AHSL-degrading strains isolated from soil samples belonged to the Bacillus genus,while strains isolated from tobacco rhizospheres belonged to both the Bacillus genus and to the α subgroup of proteobacteria,suggesting that diversity of N-AHSL-degrading strains may be modulated by the presence of the tobacco plant. Among these rhizospheric isolates,novel N-AHSL-degrading genera have been identified (Sphingomonas and Bosea). As the first simultaneous analysis of both N-AHSL-degrading and -producing bacterial communities in a complex environment,this study revealed the coexistence of bacterial isolates,belonging to the same genus or species that may produce or degrade N-AHSL.