Coupling mechanisms between microbial arsenic metabolism and carbon cycling in arsenic-contaminated groundwater

Microorganisms in groundwater play a critical role in global carbon (C) cycling. However, how arsenic (As) contamination influences microbially mediated As cycling and its coupling with C metabolism remains poorly understood. Herein, we investigated the associative coupling of microbial function genes between As and C cycling in groundwater from a typical As-contaminated industrial site in southern China. Metagenomic analyses revealed that As concentrations governed microbial community assembly, leading to distinct community structures and dominant taxa. Key microbial groups, including Pseudomonadota and Euryarchaeota, exhibited dual metabolic capabilities for both As and C transformation. Compared to the Safe group (As < 10 μg/L), the Toxic group (As > 10 μg/L) displayed greater dissimilarities in the distribution of As- and C-related functional genes. A strong correlation between As- and C-cycling genes suggests a potential trade-off mechanism between microbial As resistance and organic C utilization. Furthermore, microbial function gene-based co-occurrence networks demonstrated more complex and stable network structures in the Toxic group. The enhanced coupling between As-C functional genes likely increased microbial community resilience against environmental stressors. While observed As-C coupling mechanisms may extrapolate to chemically analogous groundwater systems, their quantitative contribution to global C budgets requires validation across diverse biogeographic contexts. This study offers novel insights into the complex coupling network between As and C metabolic pathways in groundwater microbial communities and underscores their broader implications for global biogeochemical C cycling.