Abstract
Chromate [Cr-(VI)] is a toxic heavy metal frequently detected in wastewater, often alongside nitrate (NO(3) (-)). Nitrate-dependent anaerobic methane oxidation (N-DAMO) is a promising process for the simultaneous removal of methane (CH(4)) and NO(3) (-) in wastewater treatment plants. Because Cr-(VI) can serve as an alternative electron acceptor, its presence may alter the N-DAMO performance. Here, we investigated the impact of Cr-(VI) on an enrichment culture containing Candidatus Methanoperedens and Candidatus Methylomirabilis, using NO(3) (-) as the electron acceptor and (13)C-CH(4) as the electron donor. Cultures were exposed to varying Cr-(VI) concentrations, and microbial activity was assessed using GC-MS, 16S rRNA gene sequencing, and qPCR. Cr-(VI) was reduced within the cultures, but this reduction was not linked to CH(4) oxidation. Instead, CH(4) oxidation was significantly inhibited, with declines in the relative abundances of both N-DAMO organisms. Cr-(VI) reduction was likely mediated by denitrifiers through nitrate reductase activity or abiotically via the reaction with nitrite (NO(2) (-)). These findings reveal functional resilience of microbial consortia in contaminated environments but highlight Cr-(VI) toxicity as a constraint for N-DAMO-based wastewater treatment.