PN/A Sludge Raw sequence reads. PN/A Sludge

This work unraveled discrepant ecological patterns of microbiotas between biofilms and flocs in a deteriorated bioreactor inoculating mature partial nitrification-anammox (PN/A) sludge. Results underscored that there were significantly differences between biofilms and flocs in bacterial community composition, assembly, interaction and nitrogen metabolism. The preference of specific bacteria to ecological niche and selection pressure imposed by biofilms and flocs explained the differences of bacterial community composition and structure. In light of the niche width, neutral and null models, the bacterial community assembly in both biofilms and flocs was dominantly driven by the stochastic process, and dispersal limitation critically shaped the community assembly. Co-occurrence pattern from the network analysis revealed that environmental deterioration caused decentralized and fragmented bacterial colonies, as well as AnAOB were mainly peripheral in biofilms network and less involved in interspecific interactions. Simultaneous PN/A and partial denitrification-anammox (PD/A) processes were identified, whereas PN and PD process primarily occurred in the biofilms and flocs, respectively. A complex nitrogen metabolism network existed in the system, and nitrification-denitrification bore the primary responsibility for nitrogen removal. Collectively, these outcomes are expected to deepen the basic understanding of complex microbial community and nitrogen metabolism under environmental disturbance, thereby better characterizing and serving the artificial ecosystem.