Microbial population dynamics and profiling of quorum sensing agents in membrane bioreactor

• Dominant as well as biofouling bacterial diversity in a MBR has been demonstrated.
• Biofouling bacteria showed inherently different biofilm formation tendencies irrespective of their growth rates.
• Amount of EPS required to form the matured colonies varies depending on the type of genus or species.
• QS is not solely regulated by AHLs rather, non-AHL molecules also have a key role in QS mechanism.

The biofilm formation on membrane surface in a membrane bioreactor (MBR) leads to membrane biofouling and retards the filtration performance. Researchers have been focused towards investigating the physicochemical fouling control strategies ignoring the microbiological mechanism and agents responsible for biofouling. The study aimed at investigating the signal molecules like N-acyl homoserine lactones and dominant bacterial diversity responsible for cell to cell communication, known as quorum sensing which allow them to coordinate gene expression and regulate virulence, leading to formation of mature biofilm. Dominant strains were isolated from the activated sludge of MBR and screened for the ability to produce AHLs as signal molecules, using two biosensors, Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136. 16S rRNA sequencing approach was used for identification of dominant bacterial diversity along with QS strains. Among AHLs producing strains, maximum biofilm formation ability was indicated by Pseudomonas kilonensis and Psychrobacter sp. All bacterial strains showed different biofilm forming tendencies, irrespective of their growth rate, verifies the role of QS agents responsible for biofilm development. The presence of short and medium chain AHLs (C4-HSL, C6-HSL and C8-HSL) was confirmed using HPLC. Production of AHLs and dominance of quorum sensing strains in activated sludge authenticate the key role of these substances in biofilm production and thereby membrane bio-fouling.