Seasonal dynamics of the microbial community in two full-scale wastewater treatment plants: Diversity, composition, phylogenetic group based assembly and co-occurrence pattern

The optimal operation and functional stability of a wastewater treatment plant (WWTP) strongly de-pend on the properties of its microbial community. However, a knowledge gap remains regarding the seasonal dynamics of microbial community properties, especially phylogenetic group based assembly and co-occurrence patterns. Accordingly, in this study, influent and activated sludge (AS) samples were weekly collected from 2 full-scale WWTPs for one year (89 influent and 103 AS samples in total) and examined by high-throughput Illumina-MiSeq sequencing. The results suggested that the microbial community di-versity and composition in the influent fluctuated substantially with season, while those in the AS had a relatively more stable pattern throughout the year. The phylogenetic group based assembly mechanisms of AS community were identified by using Infer Community Assembly Mechanisms by Phylogenetic-bin-based null model (iCAMP). The results showed that drift accounted for the largest proportion (52.8%), while homogeneous selection (18.2%) was the most important deterministic process. Deterministic pro-cesses dominated in 47 microbial groups (bins), which were also found (similar to 40%) in the AS core taxa dataset. Moreover, the results suggested that Nitrospira were more susceptible to stochastic processes in winter, which may provide a possible explanation for nitrification failure in winter. Network analysis results sug-gested that the network structure of the AS community could be more stable in summer and autumn. In addition, there were no identical keystone taxa found in different networks (constructed from differ-ent plants, sources, and seasons), which supported the context dependency theory. The results of this study deepened our understanding of the microbial ecology in AS systems and provided a foundation for further studies on the community regulation strategy of WWTPs. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study analyzed the seasonal dynamics of microbial communities in wastewater treatment plants, finding that microbial diversity and composition in influent fluctuated significantly, while those in activated sludge remained relatively stable throughout the year. Nitrospira were more susceptible to stochastic processes in winter, possibly explaining nitrification failure during that season. Network analysis indicated that the network structure of the activated sludge community was more stable in summer and autumn, and keystone taxa varied in different networks, supporting the context dependency theory.