Detection of Quorum Quenching Enzymes Producing Genes in Membrane Bioreactor

Abstract

Biological techniques to control the membrane biofouling issue in membrane bioreactors (MBR) for wastewater treatments are emerging since over a decade. One such an approach is the use of quorum quenching (QQ) by bacterial cells to interrupt the interspecies quorum sensing process, the later responsible for aiding in biofilm formation leading to biofouling. Therefore, to make membrane bioreactor more efficient for use, lowering the persistence biofouling is important and QQ has the potential to lower biofouling through degradation of the acyl-homoserine lactones (AHLs) involved in biofilm formation. The study attempted to isolate indigenous quorum quenching bacterial species from MBR treating real wastewater and to perform biosensor based biochemical analysis. The QQ genes in the selected species were detected by polymerase chain reaction. Furthermore, impact analysis of the QQ activity on extracellular polymeric substances (EPS) production in sequencing batch reactors (SBRs) treating wastewater inoculated with entrapped isolates in alginate beads was conducted. Majority of the bacterial isolates belonged to the genus Bacillus and Enterobacter based on 16srRNA sequencing. Biosensors analysis revealed prominent QQ activity in Pseudomonas and Bacillus species. The reported QQ genes: two acylase producing PvdQ and QuiP genes in Pseudomonas sp. QSP01, and lactonase producing AiiA gene in Bacillus sp. QSP03 and Bacillus sp. QSP10 were detected during gel documentation. These three-species entrapped in alginate beads inoculated individually and in consortia in SBRs indicated lower EPS production in comparison to non-inoculated bioreactor, all containing seeding sludge from full scale MBR treating real wastewater. It may be concluded from the study that the QQ bacterial profile of full scale MBR is different from that of pilot or laboratory scale MBR. The detection of AHL acylases and AHL lactonases producing genes in the species verified their AHL degrading capacity and gives a deeper insight into the mechanism involved in AHL degradation in MBR. Moreover, lowered EPS level was observed in SBRs having QQ entrapped alginate beads. Therefore, the QQ based biofouling control technique has the potential to lower biofouling in MBR.