Bacterial populations coexisting in the phyllosphere niche have important effects on plant health. Quorum sensing (QS) allows bacteria to communicate via diffusible signal molecules, but QS-dependent behaviors in phyllosphere bacterial populations are poorly understood. We investigate the dense and diverse N-acyl-homoserine lactone (AHL)-producing phyllosphere bacteria living on tobacco leaf surfaces via a culture-dependent method and 16S rRNA gene sequencing. Our results indicated that approximately 7.9%-11.7% of the culturable leaf-associated bacteria have the ability to produce AHL based on the assays using whole-cell biosensors. Sequencing of the 16S rRNA gene assigned the AHL-producing strains to two phylogenetic groups, with Gammaproteobacteria (93%) as the predominant group, followed by Alphaproteobacteria. All of the AHL-producing Alphaproteobacteria were affiliated with the genus Rhizobium, whereas the AHL-producing bacteria belonging to the Gammaproteobacteria mainly fell within the genera Pseudomonas, Acinetobacter, Citrobacter, Enterobacter, Pantoea and Serratia. The bioassays of supernatant extracts revealed that a portion of the strains have a remarkable AHL profile for AHL induction activity using the two different biosensors, and one compound in the active extract of a representative isolate, NTL223, corresponded to 3-oxo-hexanoyl-homoserine lactone. A large population size and diversity of bacteria capable of AHL-driven QS were found to cohabit on leaves, implying that cross-communication based AHL-type QS may be common in the phyllosphere. Furthermore, this study provides a general snapshot of a potential valuable application of AHL-producing bacteria inhabiting leaves for their presumable ecological roles in the phyllosphere.
Di LvAnzhou MaXuanming TangZhihui BaiHongyan QiGuoqiang Zhuang
