Quorum sensing signal autoinducer-2 promotes root colonization of Bacillus velezensis SQR9 by affecting biofilm formation and motility.

Root colonization of beneficial rhizobacteria is critical for their beneficial effects. Quorum sensing (QS) has been reported to affect the colonization of many plant pathogens. However, how QS signals regulate root colonization of beneficial rhizobacteria is unclear. In this study, the QS signal AI-2 synthetase-encoding gene luxS was completely deleted from the genome of the plant beneficial rhizobacterium Bacillus velezensis SQR9, and bioluminescence experiments showed that AI-2 production was blocked. Deletion of luxS reduced biofilm formation, motility, and root colonization of B. velezensis SQR9, while addition of exogenous AI-2 to the mutant restored this phenomenon. These results indicated that AI-2 positively affects the root colonization of B. velezensis SQR9. This study provided new insights for enhancing the colonization of beneficial rhizobacteria. KEY POINTS: • LuxS participated in the synthesis of the quorum sensing signal AI-2 in B. velezensis. • AI-2 enhanced motility, biofilm formation, and root colonization of B. velezensis. • AI-2 stimulated the production of γ-polyglutamic acid by B. velezensis.