How nutrients and antibiotics shape microbial network patterns: Comparative insights from Erhai Lake bays.

Freshwater lakes are increasingly subject to simultaneous nutrient enrichment and antibiotic pollution, yet the joint effects of these stressors on microbial network structure remain poorly characterized. This study examined the combined effects of nutrients and antibiotics on bacterial communities across eight bays in Erhai Lake, which were classified into high-, moderate-, and low-pollution zones. High-pollution bays (Haichao, Dongsha, and Shuanglang) recorded the region's highest nutrient concentrations, with chemical oxygen demand reaching 33.4 mg/L and total nitrogen reaching 1.5 mg/L, alongside ofloxacin levels of 8.9 ng/L. Low-pollution bays (Xiahe and Sha) had minimal contamination. Bacterial communities varied along the pollution gradient: nutrient-rich, high-pollution zones favored nutrient-tolerant species, but exhibited fragmented and unstable networks. Moderately polluted bays (Qingshan, Xiangyang, and Majiuyi) exhibited stronger antibiotic effects, characterized by the suppression of sensitive taxa and the enrichment of resistant ones, resulting in more stable and interconnected networks. Conversely, low-pollution bays exhibited well-balanced, tightly connected networks. Still, their weaker interactions may render them less resilient to disturbances such as nutrient influxes or pollution spikes than those in moderately polluted bays. This study demonstrates that natural microbial communities are highly sensitive to nutrient enrichment and antibiotic pollution. The results also indicate a critical stability period at moderate pollution levels. Managers should seize this opportunity, or the lake microbial community may tip into an unstable state marked by fragmented structure and reduced resilience, thereby compromising lake health. SYNOPSIS: Nutrient enrichment combined with high levels of antibiotics destabilizes microbial networks, compromising the resilience of the Erhai Lake ecosystem.