A Novel Quorum-Quenching N-Acylhomoserine Lactone Acylase from Acidovorax sp. Strain MR-S7 Mediates Antibiotic Resistance

N-Acylhomoserine lactone acylase (AHL acylase) is a well-known enzyme responsible for disrupting cell-cell communication (quorum sensing) in bacteria. Here, we isolated and characterized a novel and unique AHL acylase (designated MacQ) from a multidrug-resistant bacterium, Acidovorax sp. strain MR-S7. The purified MacQ protein heterologously expressed in Escherichia coli degraded a wide variety of AHLs, ranging from C(6) to C(14) side chains with or without 3-oxo substitutions. We also observed that AHL-mediated virulence factor production in a plant pathogen, Pectobacterium carotovorum, was dramatically attenuated by coculture with MacQ-overexpressing Escherichia coli, whereas E. coli with an empty vector was unable to quench the pathogenicity, which strongly indicates that MacQ can act in vivo as a quorum-quenching enzyme and interfere with the quorum-sensing system in the pathogen. In addition, this enzyme was found to be capable of degrading a wide spectrum of β-lactams (penicillin G, ampicillin, amoxicillin, carbenicillin, cephalexin, and cefadroxil) by deacylation, clearly indicating that MacQ is a bifunctional enzyme that confers both quorum quenching and antibiotic resistance on strain MR-S7. MacQ has relatively low amino acid sequence identity to any of the known acylases (<39%) and has among the broadest substrate range. Our findings provide the possibility that AHL acylase genes can be an alternative source of antibiotic resistance genes posing a threat to human health if they migrate and transfer to pathogenic bacteria. IMPORTANCE N-Acylhomoserine lactones (AHLs) are well-known signal molecules for bacterial cell-cell communication (quorum sensing), and AHL acylase, which is able to degrade AHLs, has been recognized as a major target for quorum-sensing interference (quorum quenching) in pathogens. In this work, we succeeded in isolating a novel AHL acylase (MacQ) from a multidrug-resistant bacterium and demonstrated that the MacQ enzyme could confer multidrug resistance as well as quorum quenching on the host organism. Indeed, the purified MacQ protein was found to be bifunctional and capable of degrading not only various AHL derivatives but also multiple β-lactam antibiotics by deacylation activities. Although quorum quenching and antibiotic resistance have been recognized to be distinct biological functions, our findings clearly link the two functions by discovering the novel bifunctional enzyme and further providing the possibility that a hitherto-overlooked antibiotic resistance mechanism mediated by the quorum-quenching enzyme may exist in natural environments and perhaps in clinical settings.