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.