Microbial community composition and cooccurrence patterns driven by co-contamination of heavy metals and chlorinated...

Electroplating activities release mixtures of heavy metals and chlorinated hydrocarbons, posing significant risks to groundwater ecosystems. However, the ecological responses and adaptive mechanisms of groundwater microbiota to such co-contamination remain poorly understood. In this study, we investigated microbial community composition, diversity, co-occurrence networks and assembly patterns in groundwater affected by both heavy metals and chlorinated hydrocarbons. Contaminants included Fe, Mn, Ni, Zn, Cr, and chlorinated hydrocarbons, with nickel and cis-1,2-dichloroethene exhibiting the highest exceedances, reaching 1027-fold and 2060-fold, respectively. Microbial community structure differed significantly across low-pollution (LP), metal-pollution (MP), and complex-pollution (OP) zones. The MP zone exhibited higher microbial diversity, network complexity, and connectivity, suggesting enhanced microbial interactions under moderate metal stress. In contrast, the OP zone experienced high intensity and multi-factor stress, leading to reduced diversity and simplified network complexity. Key taxa, including Vampirovibrionaceae, Hyphomicrobium, Sphingomonas, and Dethiobacter, played critical roles in maintaining network stability. pH and 1,2-dichloroethane were identified as primary drivers shaping both microbial community composition and network structure. Community assembly in groundwater was predominantly governed by stochastic processes, particularly dispersal limitation. Homogeneous selection was strengthened under persistent and spatially uniform metal stress in the MP zone, whereas heterogeneous selection became more prominent in the OP zone, dissolved organic carbon emerged as a central regulator of both homogeneous selection and dispersal limitation. Our findings provide new insights into groundwater ecosystem adaptation and offering ecological implications for microbial-based remediation strategies.