N-Acyl-homoserine lactone-mediated quorum sensing of aerobic granular sludge system in a continuous-flow membrane bioreactor

Abstract

The investigation aimed at revealing the N-acyl-homoserine lactone (AHL)-mediated quorum sensing (QS) of aerobic granular sludge (AGS) system in a membrane bioreactor (MBR) with internal circulation. During the experimental period, the MBR was operated under a continuous-flow mode, in which, AGS was cultivated directly. The specific AHL molecules were determined and the correlation between the AHL-mediated QS, extracellular polymeric substance (EPS) production and microbial community was explored. Two kinds of specific signaling molecule, N-octanoyl-dl- homoserine lactone (C8-HSL) and N-tetradecanoyl-dl-homoserine lactone (C14-HSL), were detected in the cultivated AGS, but C14-HSL was the major one, which was detected to be ranging from 86.58 ng/gMLSS to 594.00 ng/gMLSS among all samples. Most importantly, the concentration of C14-HSL was positively correlated to the production of LB-EPS and TB-EPS (r > 0.906, P < 0.034, minimum ‘r’ and maximum ‘p’), which demonstrated it’s a crucial component in the formation of AGS and determined its stability. The results indicated that the structure of microbial community showed weak correlation with the content of AHLs and EPS if without the pressure of microbial selection. But, the conditions within the bioreactor determined the microbial community, and the contained functional bacteria released signaling molecules to promote the granulation.