Interference of Quorum Sensing by <i>Delftia</i> sp. VM4 Depends on the Activity of a Novel <i>N</i>-Acylhomoserine Lactone-Acylase

<div><p>Background</p><p>Turf soil bacterial isolate <i>Delftia</i> sp. VM4 can degrade exogenous <i>N</i>-acyl homoserine lactone (AHL), hence it effectively attenuates the virulence of bacterial soft rot pathogen <i>Pectobacterium carotovorum</i> subsp. <i>carotovorum</i> strain BR1 (Pcc BR1) as a consequence of quorum sensing inhibition.</p><p>Methodology/Principal Findings</p><p>Isolated <i>Delftia</i> sp. VM4 can grow in minimal medium supplemented with AHL as a sole source of carbon and energy. It also possesses the ability to degrade various AHL molecules in a short time interval. <i>Delftia</i> sp. VM4 suppresses AHL accumulation and the production of virulence determinant enzymes by Pcc BR1 without interference of the growth during co-culture cultivation. The quorum quenching activity was lost after the treatment with trypsin and proteinase K. The protein with quorum quenching activity was purified by three step process. Matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) and Mass spectrometry (MS/MS) analysis revealed that the AHL degrading enzyme (82 kDa) demonstrates homology with the NCBI database hypothetical protein (Daci_4366) of <i>D</i>. <i>acidovorans</i> SPH-1. The purified AHL acylase of <i>Delftia</i> sp. VM4 demonstrated optimum activity at 20–40°C and pH 6.2 as well as AHL acylase type mode of action. It possesses similarity with an α/β-hydrolase fold protein, which makes it unique among the known AHL acylases with domains of the <i>N</i>-terminal nucleophile (Ntn)-hydrolase superfamily. In addition, the kinetic and thermodynamic parameters for hydrolysis of the different AHL substrates by purified AHL-acylase were estimated. Here we present the studies that investigate the mode of action and kinetics of AHL-degradation by purified AHL acylase from <i>Delftia</i> sp. VM4.</p><p>Significance</p><p>We characterized an AHL-inactivating enzyme from <i>Delftia</i> sp. VM4, identified as AHL acylase showing distinctive similarity with α/β-hydrolase fold protein, described its biochemical and thermodynamic properties for the first time and revealed its potential application as an anti-virulence agent against bacterial soft rot pathogen <i>Pectobacterium carotovorum</i> subsp. <i>carotovorum</i> based on quorum quenching mechanism.</p>