Novel metabolic pathways of bioelectrochemical vanadate reduction by Thiobacillus denitrificans without exogenous electron donor supplementation in groundwater

Microbially mediated vanadate [V(V)] reduction is well accepted as a sustainable approach for remediating V-polluted groundwater. However, this process relies on exogenous electron donors, which is challenging to control precisely and inject into aquifer. In this study, bioelectrochemical V(V) reduction by autotrophic Thiobacillus denitrificans was demonstrated without exogenous electron donor supplementation. At an applied voltage of 0.9 V, 94.5 ± 0.95 % of V(V) was removed within 14 d V(V) was mainly bioreduced at the cathode. Insoluble tetravalent V was the main reduction product, distributed both outside and inside of cells. Electrochemical analysis, transcriptomics, RT-qPCR and substance quantification analysis collectively suggested that extracellular V(V) reduction was mediated by cytochrome c and extracellular polymeric substances. Intracellular V(V) reduction was catalyzed by sulfate-, chromate-, and denitrification-related reductases and achieved by redox components including NADH, Fe-S clusters, and quinones in respiratory chain. Particularly, the newly V(V) reduction pathways of the functional genes aprB and iscA were further confirmed via in vitro trials involving heterologous expression and protein catalysis assays. This study provided an innovative strategy for V(V) bioremediation in groundwater and gained novel insight into molecular mechanisms of V(V) bioreduction.