Quorum-sensing contributes to virulence, twitching motility, seed attachment and biofilm formation in the wild type strain Aac-5 of Acidovorax citrulli

• The deletion of aacR and aacI genes resulted in reduced virulence and twitching motility of Acidovorax citrulli strain Aac-5.
• Compared to WT strain, the biofilm formation and seed attachment were increased in the two mutant strains.
• Deletion of aacR and aacI had no effect on swimming motility and polar flagella formation of Aac-5.

Acidovorax citrulli is a seed-borne pathogen causing bacterial fruit blotch of cucurbits including melon and watermelon. We investigated the roles of quorum sensing in the wild-type group II strain Aac-5 of A. citrulli by generating aacR and aacI knockout mutants and their complementation strains. We found that twitching motility and virulence were reduced, but biofilm formation and seed attachment were increased significantly in the two mutants as compared to the wild type strain. Deletion of aacR and aacI, however, had no effect on swimming motility and polar flagella formation of Aac-5. Furthermore, deletion of aacR resulted in reduced gene expression of hrpE, hrcN and pilT, while deletion of aacI affected only the expression of hrpE and pilT, not hrcN.