Microbial-Mediated Coevolution of Vanadium and Ferric Iron Minerals in Sedimentary Environments

Rising vanadium(V) contamination severely threatens environmental safety and human health. Microbial-mediated pentavalent V [V(V)] reduction, an effective route to V detoxification, can be influenced by coexisting redox-sensitive matters. However, the interaction between V(V) and widely distributed ferric iron [Fe(III)] minerals still remains largely unknown. This study investigated the coupled transformations of V(V) and Fe(III) minerals in biosystems with Bacillus subtilis. Fe(III) minerals, particularly low-crystallinity ferrihydrite, markedly enhanced V(V) reduction. Concurrently, B. subtilis reduced structural Fe(III) to Fe(II), which abiotically drove V(V) reduction, contributing 62.6, 60.6, and 45.3% of total V(V) removal in ferrihydrite, goethite, and hematite biosystems, respectively. X-ray photoelectron spectroscopy, X-ray diffraction, and X-ray absorption near-edge structure analysis revealed that V(V) was reduced predominantly to VO(OH)₂ precipitates. Nanoscale goethite formed concurrently in ferrihydrite biosystem, with goethite and hematite biosystems showing minimal mineralogical change. Elevated levels of cytochrome and extracellular polymeric substances enhanced extracellular electron transfer, facilitating V(V) and Fe(III) reductions. The upregulation of genes napA and cnorB with increased activities of nitrate reductase and nitric oxide reductase further reinforced reductive V(V) detoxification. These findings provide novel insights into biogeochemical interactions between V and Fe(III) minerals and offer a promising strategy for detoxifying V in sedimentary environments.