Distinct mechanisms underlying assembly processes and interactions of microbial communities in two single-stage bioreactors coupling anammox with denitrification

Coupling anammox with denitrification processes are promising technologies for total nitrogen removal from wastewater. However, the assembly processes and interactions of functional bacteria in the coupling systems are still poorly understood. Herein, two lab-scale up-flow bioreactors were separately operated to achieve the simultaneous anammox and denitrification (SAD) and the partial denitrification and anammox (PDA) systems under different substrate loading conditions. Although the two bioreactors seemed to have similar composition of functional bacteria, denitrifying bacteria Denitratisoma and Thauera exhibited higher abundances in the PDA bioreactor. In contrast, the genus Candidatus Jettenia was more abundant in the SAD bioreactor. The null model showed that stochastic processes dominantly governed the community assembly in both bioreactors across different substrate loadings. However, homogeneous selection appeared to be more important for shaping communities in the SAD system under high and moderate substrate-loading conditions. Particularly, drift was the most important process in driving the assembly of dominant denitrifying bacteria (e.g. genera Denitratisoma and Thauera), whereas anammox bacteria were primarily governed by the homogenous selection under high substrate-loading conditions. Moreover, anammox and denitrifying bacteria in the PDA bioreactor established simple and efficient networks, probably exerting impacts on the assembly processes of their co-occurring species. By contrast, the networks in the SAD bioreactor showed low modularity and interconnectivity. This study highlighted the specificity of community assembly processes and interactions in SAD and PDA systems, which would advance our understanding of the fundamental ecological laws underpinning the collaboration of anammox and denitrifying bacteria.

Automated summary

This study investigated the assembly processes and interactions of functional bacteria in anammox and denitrification coupling systems using lab-scale up-flow bioreactors. The results showed that the community composition of functional bacteria differed between the systems, and the community assembly was mainly governed by stochastic processes and homogeneous selection. Moreover, the network structures of anammox and denitrifying bacteria varied between the systems.