Identification and Characterization of the Quorum Quenching Enzymes in Bacterial Strains Isolated from Sludge of Membrane Bioreactor

Abstract

Antibiotic resistance has led to the emergence of `superbugs` that are bacteria resistant to multiple drugs commonly prescribed for treatment of bacterial infections. Currently we are left with very limited options to combat these infections. Many novel antibacterial approaches are under investigation. Quorum Sensing has been reported to be extensively involved in causing bacterial infections. It includes synthesis of signaling molecules for intercellular communication of bacteria. Identification of Quorum Sensing signaling molecules has led to the discovery of new targets to inhibit infections. These signaling molecules can be targeted at their production, after production or at their recognition site by receptor protein. This process is known as Quorum Quenching and can serve as a powerful tool to combat multidrug resistant infections without imposing selection pressure on bacteria thus eliminating the risk of antimicrobial resistance. In the present study, bacteria responsible for degradation of signal molecules in the bacterial pathogens have been isolated from sludge of membrane bioreactor. Four of the isolated strains showed maximum growth on minimal media with Acyl Homoserine Lactones (AHLs), signaling molecules in bacteria, as their sole Carbon and Nitrogen source. These strains were characterized for their ability to degrade AHLs and were checked for their inhibition effect on biofilms formed by the pathogenic Pseudomonas aeruginosa. After 16S rDNA sequencing, these four strains were verified at the species level as Bacillus cereus strain QSP03, Bacillus subtilis strain QSP10, Pseudomonas putida strain QQ3 and Pseudomonas aeruginosa strain QSP01. Presence of three Quorum Quenching enzymes (AHL lactonases and AHL acylases) producing genes, AiiA, PvdQ and QuiP was confirmed via respective primers and sequencing. The AHL degradation capability and identification of respective enzyme producing genes indicates the current bacterial isolates to be potential Quorum Quenching strains.