Responses of microbial interactions to elevated salinity in activated sludge microbial community

Biological treatment processes are critical for sewage purification, wherein microbial interactions are tightly associated with treatment performance. Previous studies have focused on assessing how environmental factors (such as salinity) affect the diversity and composition of the microbial community but ignore the connections among microorganisms. Here, we described the microbial interactions in response to elevated salinity in an activated sludge system by performing an association network analysis. It was found that higher salinity resulted in low microbial diversity, and small, complex, more competitive overall networks, leading to poor performance of the treatment process. Subnetworks of major phyla (Proteobacteria, Bacteroidetes, and Chloroflexi) and functional bacteria (such as AOB, NOB and denitrifiers) differed substantially under elevated salinity process. Compared with subnetworks of Nitrosomonadaceae, Nitrosomonas (AOB) made a greater contribution to nitrification under higher salinity (especially 3%) in the activated sludge system. Denitrifiers established more proportion of cooperative relationships with other bacteria to resist 3% salinity stress. Furthermore, identified keystone species playing crucial roles in maintaining process stability were dynamics and less abundant under salinity disturbance. Knowledge gleaned from this study deepened our understanding of microbial interaction in response to elevated salinity in activated sludge systems.

Automated summary

Biological treatment processes play a crucial role in sewage purification, and microbial interactions have a significant impact on treatment performance. This study investigated the microbial interactions in an activated sludge system under elevated salinity using association network analysis. The results showed that higher salinity led to lower microbial diversity and more competitive overall networks, resulting in reduced treatment process efficiency. The subnetworks of major phyla and functional bacteria differed significantly under elevated salinity, with Nitrosomonas making a greater contribution to nitrification and denitrifiers establishing more cooperative relationships to resist salinity stress. Keystone species crucial for process stability were found to be dynamic and less abundant under salinity disturbance. This study deepened our understanding of microbial interactions in activated sludge systems under elevated salinity.