Metagenomic analysis of quorum sensing systems in activated sludge and membrane biofilm of a full-scale membrane bioreactor

Biofouling hampers the long-lasting operation of membrane bioreactor (MBR) and quorum sensing (QS) can be applied to control biofouling. In this study, N-acyl homoserine lactones (AHLs), QS/quorum quenching (QQ) functional genes, and microbial communities in activated sludge and membrane biofilm from a full-scale MBR were analyzed. Types and concentrations of AHLs in activated sludge and membrane biofilm were remarkably different. The major AHLs detected in membrane biofilm were N-decanoyl-L-homoserine lactone, N-dodecanoyl-L-homoserine lactone and N-3-oxo-decanoyl-L-homoserine lactone, while N-butyryl-L-homoserine lactone and N-octanoyl-L-homoserine lactone were dominant in activated sludge. The concentration of AHLs in membrane biofilm (1439.4 ng/g VSS) was 1.1 folder higher than that in activated sludge (676.7 ng/g VSS). All QS systems, AHLs, AI-2, DSF, PQS, AIP and c-di-GMP, were enhanced in membrane biofilm, with more types and higher abundances of genes and microorganisms. The QQ system was suppressed in membrane biofilm. Additionally, Nitrospira, Nitrosomonas, Candidatus Accumulibacter and Dechloromonas, the dominant microorganisms for nitrogen removal in membrane biofilm, also harbored diverse QS/QQ genes. The microorganisms responsible for both nitrogen removal and QS/QQ accounted for 14.1% in total bacteria of membrane biofilm (while 7.8% in activated sludge). The nitrogen removal system might contribute to the biofouling formation. This study provided useful information for biofouling control by regulating QS and QQ in full-scale MBRs.