Distinct assembly processes and interspecies interactions between anammox bacteria and co-occurring species across...

Anammox bacteria tend to form granules in engineered systems, but little is known about the ecological mechanisms governing anammox bacteria and their co-occurring species in anammox aggregates. Herein, the microbial community, assembly processes and interspecies interactions were investigated using 200 randomly collected anammox granules from two contrasting environments: a full-scale swine wastewater treatment plant (SwAmx) and a lab-scale up-flow column reactor (LuAmx) treating synthetic wastewater. Granules diameter showed no strong correlation with microbial community in either system, despite functional bacteria Candidatus Brocadia and Denitratisoma maintaining high relative abundance with low heterogeneity across anammox granules. Both neutral and null model analysis revealed that stochastic processes dominated community assembly, with dispersal limitation accounting for 71.51-89.75 % of community assembly, indicating limited microbial exchange between granules. Notably, deterministic selection (especially for homogeneous selection) emerged as the main driver (10.20-26.47 % contribution) for nitrifying and denitrifying bacteria, likely influenced by complex wastewater composition in SwAmx system. The co-occurrence networks further revealed prevalent negative correlations (60.00-90.91 % of connections) between anammox bacteria and heterotrophic populations in both systems, implying potential resource competition. These multiscale insights underscored the ecological drivers in whole anammox community and individual groups, and provided critical implications for optimizing nitrogen removal performance through microbial community management.