Revealing real impact of microalgae on seasonal dynamics of bacterial community in a pilot-scale microalgal-bacterial consortium system.

The microalgal-bacterial consortium (MBC) system is recognized as an advanced approach for nitrogen and phosphorus removal in wastewater treatment. However, the influence of microalgae on bacterial community dynamics and niche differentiation across varying seasonal conditions remains unexplored. In this study, we established a pilot-scale continuous-flow MBC system to disentangle, for the first time, the impact of microalgae on seasonal bacterial community succession by conducting monthly time-series sampling over a full seasonal cycle. Notably, a core microbiome consisting of 528 ASVs displaying significant seasonal rhythms was identified in both activated sludge (AS) and MBC systems. Unlike the random drift-driven assembly observed in the AS system, microalgae can recruit dominant species that respond to environmental fluctuations to form a core microbiome (heterogeneous selection), thereby enhancing community stability. Concurrently, microalgae facilitated niche differentiation within the core microbiome, driving transition from generalist to specialist species, which in turn promoted synergistic interactions that can improve nitrification and denitrification functions. Additionally, microalgae strengthened the correlation between functional species in the core microbiome and seasonal variations in light and temperature, as well as with regulating the efficiency of nitrogen and phosphorus removal by influencing the abundance of these functional species. These findings deepen our understanding of bacterial ecology based on microalgae management and provide a foundation further for the study of community regulation strategy of MBC systems.