Lianfu Liang, Xiaofeng Fu, Yuqing Ding, Keying Liu, Rui Lin, Zhaojin Chen
Anaerobic oxidation of methane (AOM) coupled with Cr(VI) bioreduction process offers a cost-effective pathway to simultaneously mitigate methane emissions and remediate Cr(VI) contamination. However, its practical application is limited by insufficient intracellular energy generation and low electron transfer efficiency. This study elucidated the regulatory role and mechanism of Na+, a transmembrane electrochemical gradient driver, on the metabolic activity and electron transfer of this coupled system. Batch experiments demonstrated that NaCl addition significantly improved Cr(VI) reduction efficiency, achieving complete removal in the treatment group by the end of the first cycle compared to only 79.8 % in the control. Microbial community analysis showed that Na+ enriched AOM-capable Methanobacterium and extracellular electron transfer (EET)-capable electroactive bacterium unclassified_o_DTU014, which likely formed a syntrophic consortium to mediate Cr(VI) reduction. Electrochemical measurements and 3D-EEM spectroscopy revealed that Na+ enhanced microbial aggregate electron storage capacity, reduced electron transfer resistance, and promoted extracellular polymeric substance (EPS) secretion of tyrosine-like proteins and humic acid-like substances, thereby strengthening extracellular electron transfer. Key metabolic indicators showed 26.2 % higher coenzyme F420 and 37.4 % higher intracellular ATP levels in Na+-treated groups. Metagenomic analysis confirmed that Na+ upregulated genes encoding reverse methanogenesis enzymes (Mcr, Mtr) and membrane-bound electron transfer complexes (Fpo, HdrDE), while downregulating intracellular chromate reductase (ChrR) genes, indicating that EET-mediated extracellular Cr(VI) reduction played a critical role under Na+ stimulation. This study first reveals the mechanism of Na+-promoted AOM-coupled Cr(VI) reduction via enhanced energy metabolism and electron transfer, providing a crucial theoretical basis for methane-driven Cr(VI) remediation.