Cellulose-induced shifts in microbial communities and microbial interactions in an anoxic/aerobic membrane bioreactor

The roles of influent cellulose in regulating bio-system performance and microbial community structure remain largely unknown. Here, we investigated the wastewater treatment performance, microbial diversity along with interspecific interaction in a membrane bioreactor (MBR) in the presence and absence of influent cellulose. The results showed that the presence of cellulose did not affect reactor performance significantly, including the removal of total nitrogen and organics (P > 0.05 for both). However, the absence of influent cellulose decreased the biodiversity of bacterial and fungal community as compared with the presence of cellulose. Thus, the community structure between the two scenarios was significantly different. Proteobacteria (39.2 %-51.0 %), Chloroflexi (25.2 %-18.7 %) and Bacteroidetes (16.0 %-15.9 %) were the top 3 dominant phyla, and cellulosedegrading populations, most of which were affiliated with Bacteroidetes (e.g., Flavobacterium, Acetobacteroides) and Firmicutes (e.g., Exiguobacterium), showed higher relative abundance when being fed with cellulose. Phylogenetic molecular ecological networks (pMENs) indicated that biotic interactions were weaker in the presence of cellulose and possessed higher proportion of competitive relationships. The keystone microbes including nitrogen and cellulose metabolism associated taxa were inconsistent between the two scenarios. Cellulose decomposer (Bryobacter and OM190), nitrifier (Nitrospira) and denitrifier (Sulfuritalea) were the keystone microbes in the presence of cellulose, while the species belonging to Chloroflexi (Anaerolineaceae, Kouleothrix) played important roles in the absence of cellulose. This study highlights the important roles of cellulose in shaping microbial community structure and advances our understanding of characteristics of microbial ecology regulated by cellulose in MBR systems.