Assembly and interactions of denitrifying and anammox communities in a typical eutrophic lake

Abstract Nitrogen removal is crucial for controlling nitrogen levels in eutrophic lakes and depends on the high transformation capacity of nitrogen-cycling microorganisms. However, the assembly mechanisms and interactions of nitrogen removal microbial communities in lake water remain unclear. This study aimed to clarify how nitrogen levels influence the diversity, interactions, and assembly of denitrifying and anaerobic ammonia oxidation (anammox) communities. We collected lake water from different areas in a typical eutrophic lake and investigated the nitrogen removal bacterial communities by high-throughput sequencing of two representative functional genes (nirS and hzsB). Our results indicated that the α-diversity of anammox bacteria was higher in sites with high concentration of nitrogen (> 1.5 mg/L) than in sites with low concentration of nitrogen (< 1.5 mg/L). Anammox bacteria in high-nitrogen sites were dominated by the potential keystone taxon Candidatus Brocadia. Co-occurrence network analysis revealed that low-nitrogen sites had more negative connections between denitrifying and anammox communities. Moreover, total nitrogen and electrical conductivity were key factors determining community structure. Microbial community assembly analysis indicated that both denitrifying and anammox communities were primarily governed by stochastic processes across different nitrogen levels. This study enhanced our understanding of microbial community dynamics in nitrogen removal processes in eutrophic lakes.