Emerging contaminant gradients drive deterministic assembly and cooperative networks of sediment bacterial community in China's second largest freshwater lake.

The influence of emerging contaminants (ECs) on the sediment bacterial community has been largely ignored by researchers because their concentrations are relatively low in aquatic ecosystems. In this study, the ecological responses of sediment bacterial communities to concentration gradients of 44 ECs in Dongting Lake, the second largest freshwater lake in China, were examined by integrating DNA-based methods, co-occurrence network analysis, and a null model. Due to human activities and hydrochemical processes, the total concentrations of ECs in sediments ranged from 1.41 to 59.00 ng g-1, with macrolides and sulphonamides identified as the major groups. The accumulation of ECs significantly affected the β diversity of bacterial communities across geographic scales (P < 0.05), along with an increase in α diversity and enrichment of tolerant taxa, resulting in a broader metabolic niche. Adaptation to ECs also shifted community assembly from mainly stochastic processes (75 % at low-EC sites) to deterministic homogeneous selection (56 % at high-EC sites). Additionally, co-occurrence networks under high EC levels exhibited more positive interactions, higher modularity, lower intermodule connectivity, and an increased number of keystone taxa, indicating that niche differentiation and cooperative interactions act as adaptive mechanisms. Steroidobacteraceae and Clostridium sensu stricto 1 were identified as keystone species and biomarkers for contamination by ECs. These findings highlight that EC gradients restructure sediment microbiomes by promoting deterministic assembly and modifying ecological interactions, with implications for ecosystem resilience under contaminant stress.