Inhibition of QS-regulated virulence factors in Pseudomonas aeruginosa PAO1 and Pectobacterium carotovorum by AHL-lactonase of endophytic bacterium Bacillus cereus VT96

Expression of virulence factors in Pseudomonas aeruginosa and Pectobacterium carotovorum is regulated by quorum sensing signals, predominantly belonging to acyl homoserine lactones (AHLs). Hence, effective quorum quenching mechanism could be a promising strategy to suppress the virulence of these pathogens. The cell-free lysate of endophytic bacterium Bacillus cereus VT96 isolated from Ventilago madraspatana Gaertn., showed significant quorum quenching activity when assayed using biosensor strains. An AHL-lactonase enzyme encoded by aiiA gene, possessing a conserved motif 104HXHXDH109 for zinc metal binding and tyrosine residue was partially purified from the cell-free lysate of B. cereus VT96 and tested against the expression of virulence factors in Pseudomonas aeruginosa PAO1. The enzyme effectively inhibited biofilm formation and production of pyocyanin, rhamnolipid and exopolysaccharides in P. aeruginosa. P. carotovorum was selected as the in vitro model for testing the efficacy of enzyme, where the enzyme effectively reduced the tissue maceration in potato tuber, which evidently demonstrated the control of QS regulated pathogenicity. Therefore, the AHL-lactonase from endophytic strain of B. cereus VT96 could be exploited to control AHL mediated QS dependent virulence factors of pathogens in clinical and biocontrol applications.