New insights to the difference in microbial composition and interspecies interactions between fouling layer and mixed liquor in a membrane bioreactor

This work examined fouling-associated microbial community in a carefully controlled laboratory-scale membrane bioreactor (MBR) at different fouling stages. In agreement with the literature, fouling severity was positively correlated with bound polysaccharide and protein content (indicators) in the mixed liquor. UPGMA clustering analysis with different indices indicated that although the biofouling layer (biofilm) and mixed liquor possessed highly similar microbial identity, important differences between the two communities' structures were also observed. This appears to be the first comprehensive study to apply differential abundance analysis (ANCOM) to identify microbial taxa driven the divergence in microbial structure including Victivallales, Coxiellales, unassigned Microgenomatia and Blastocatellia 11-24 (all presented at 1% abundance). Network analysis also identified Victivallales and Blastocatellia 11-24 among the few key players in the mixed liquor and biofilm community, respectively. Despite their low abundances, key players in both communities positively correlated (Pearson's correlation coefficient 0.6) with fouling indicators, confirming their important contributions to fouling propensity. The biofilm community exhibited a more complex structure with higher level of inter-species interaction and prevalence of positive connections (74.6%) compared to the mixed liquor community (42.2%), reflecting higher stability and synergy between microbial taxa in the biofilm. Results from this comprehensive investigation can support the development of new fouling control strategies.