Résumé
Quorum sensing (QS) is a cell-cell communication mechanism that allows bacterial populations to coordinate gene expression in response to cell density. N-acylhomoserine lactones (AHL) are used as quorum-sensing signal molecules by many Gram negative bacteria. Acinetobacter sp. 77, an AHL-degrading bacterium, was isolated in our previous work. The gene aidE for AHL inactivation was cloned in this study by screening a genomic DNA library. The deduced protein AidE is 268 amino acids in length and shares a high identity (95%) with the beta-lactamase family protein in Acinetobacter gyllenbergii CIP110306, but low identities with known AHL-degrading enzymes. HPLC analysis of the AidE-degraded C6-HSL products revealed that AidE functioned as an AHL lactonase. Sequences alignment suggested that the aidE gene is not conserved in Acinetobacter species, flanking sequences of aidE and their arrangement are specific in Acinetobacter sp. 77 genome, and some IS insertion sequences were found downstream of the aidE gene. These evidences indicated that the aidE gene might be foreign DNA taken up via horizontal gene transferring or had changed its relative location due to the genome rear-arrangement. Expression of the aidE gene in Pectobacterium carotovorum subsp. carotovorum Z3-3 significantly reduced its AHL production as well as the pathogenicity on host plants, indicating that AidE was able to effectively quench quorum sensing-dependent functions in bacteria. In conclusion, aidE is a newfound AHL-lactonase with a potential for suppression of bacterial infections.