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Hexavalent Chromium Inhibits Nitrate-Dependent Anaerobic Methane Oxidation While Enriching Denitrifiers: Insights
Yinxiao Ma1,2, Garrett Smith3, Suzanne S C M Haaijer-Vroomen1
1Department of Microbiology, Radboud Institute for Biological and Environmental Sciences, Radboud University, Nijmegen 6525AJ, The Netherlands.
Abstract:
Chromate [Cr-(VI)] is a toxic heavy metal frequently detected in wastewater, often alongside nitrate (NO3 -). Nitrate-dependent anaerobic methane oxidation (N-DAMO) is a promising process for the simultaneous removal of methane (CH4) and NO3 - 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 NO3 - as the electron acceptor and 13C-CH4 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 CH4 oxidation. Instead, CH4 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 (NO2 -). 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.
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