Silencing of Erwinia amylovora sy69 AHL‐quorum sensing by a Bacillus simplex AHL‐inducible aiiA gene encoding a zinc‐dependent N‐acyl‐homoserine lactonase

Quorum sensing in Gram-negative bacteria is regulated by diffusible signal molecules called N-acyl-l-homoserine lactones (AHLs). These molecules are degraded by lactonases. In this study, six Bacillus simplex isolates were characterized and identified as a new quorum-quenching species of Bacillus. An aiiA gene encoding an AHL-lactonase was identified based on evidence that: (i) it showed high homology with other aiiA genes of Bacillus sp.; (ii) the deduced amino acid sequence contained two conserved regions, 104SHLHFDH111 and 165TPGHTPGH173, characteristic of the metallo-β-lactamase superfamily; and (iii) the protein had zinc-dependent AHL-degrading activity. Additionally, the expression of the aiiA gene was significantly up-regulated by 3-oxo-AHL. The AHL-lactonase inhibited multiplication of the 3-oxo-C6-AHL-producing plant pathogen Erwinia amylovora sy69 both in vitro and in planta. The results provide support for the use of the quorum-quenching functionality of B. simplex in the integrated control of the devastating fire blight pathogen.