Interaction of with Quorum Sensing and Quorum Quenching Bacteria Mediated by Root Exudates in a Consecutive Monoculture System.

Many plant-pathogenic bacteria are dependent on quorum sensing (QS) to evoke disease. In this study, the population of QS and quorum quenching (QQ) bacteria was analyzed in a consecutive monoculture system of . The isolated QS strains were identified as with -type QS system and exhibited a significant increase over the years of monoculture. Only one QQ strain was isolated from newly planted soil sample and was identified as , which secreted lactonase to degrade QS signal molecules. Inoculation of to root could rapidly cause wilt disease, which was alleviated by . Furthermore, the expression of lactonase encoded by the gene in resulted in reduction of its pathogenicity, implying that the toxic effect of on the seedlings was QS-regulated. Meanwhile, excess lactonase in led to reduction in antibacterial substances, exoenzymes, and swarming motility, which might contribute to pathogensis on the seedlings. Root exudates and root tuber extracts of significantly promoted the growth of , whereas a slight increase of was observed in both samples. These results demonstrated that QS-regulated behaviors in mediated by root exudates played an important role in replanting diseases of .