The acyl-homoserine lactone (AHL)-type quorum sensing system affects growth rate, swimming motility and virulence in Acidovorax avenae subsp. citrulli

Abstract

Acidovorax avenae subsp. citrulli is a Gram-negative bacterium and is the causal agent of bacterial fruit blotch (BFB) in cucurbits. In this study, the role played by the acyl-homoserine lactone (AHL)-type quorum sensing (QS) system in growth, swimming motility and virulence was characterized in A.avenae subsp. citrulli strain XJL12. The AHL synthase gene of the QS system from strain XJL12, defined as aacI, was cloned and characterized, and an aacI disruption mutant was generated. The aacI mutant XJL13 abolished the ability to produce AHL molecules, whereas the corresponding complemented strain CPXJL13 produced wild-type levels of AHL. The aacI mutant exhibited a significant decrease in growth rate relative to the wild type in minimal medium, and was partially impaired in swimming motility. In plants, the aacI mutant showed a significant reduction of virulence in watermelon fruits and melon seedlings when compared to the wild-type strain. However, the aacI mutation in strain XJL12 had no effects on biofilm formation, exopolysaccharide production, or induction of hypersentitive response in Nicotiana tabacum. Our data suggest that the AHL-type QS may play a key role in pathogen virulence and this may provide an opportunity to explore novel approaches for managing BFB in cucurbits by QS interference.