Photolytic quorum quenching effects on the microbial communities and functional gene expressions in membrane bioreactors

Photolytic quorumquenching by ultraviolet A (UVA) irradiation is an effective strategy for controlling membrane bioreactor (MBR) biofouling; however, its effects on MBR microbial communities and functional genes have not yet been explored. Here, we report on the effects of the UVA irradiation, which mitigates membrane biofouling, on the microbial community structures, alpha and beta diversities, and functional gene expressions in the MBR mixed liquor and biocake (membrane fouling layer) for the first time. The results show that the microbial communities become less diversified when alternating UVA is applied to the MBRs. The changes in the community structure are highly influenced by spatiotemporal factors, such as microbial habitats (mixed liquor and biocake) and reactor operation time, although UVA irradiation also has some impacts on the community. The relative abundance of the Sphingomonadaceae family, which can decompose the furan ring of autoinducer-2 (AI-2) signal molecules, becomes greater with continuous UVA irradiation. Xanthomonadaceae, which produces biofilm-degrading enzymes, is also more abundant with UVA photolysis than without it. Copies of monooxygenase and hydroxylase enzyme-related genes increase in the MBR with longer UVA exposures (i.e., continuous UVA). These enzymes seem to be inducible by UVA, enhancing the AI-2 inactivation. In conclusion, UVA irradiation alters the microbial community and the metabolism in the MBR, contributing to the membrane biofouling mitigation.

Automated summary

This study investigates the effects of UVA irradiation on microbial community structures, diversity, and functional gene expressions in MBR. The results show that UVA irradiation reduces microbial diversity in MBRs. The changes in community structures are influenced by spatiotemporal factors and UVA irradiation itself. The relative abundance of certain microbial families associated with decomposition of signal molecules and biofilm degradation increases with UVA photolysis. In addition, certain enzyme-related gene copies increase with longer UVA exposures. These findings suggest that UVA irradiation can alter microbial community and metabolism in MBR, contributing to the mitigation of membrane biofouling.