Reduction of Pentavalent Vanadium via Enhanced Levels of Sulfhydryl by Elemental Sulfur Reducing Bacteria from a Stone Coal Mining Region

Microbial reduction of pentavalent vanadium [V(V)] to less toxic tetravalent vanadium [V(IV)] is associated with the biogeochemical cycling of sulfur. However, the capability of elemental sulfur-reducing bacteria (S0RB) to reduce V(V) in the presence of elemental sulfur (S0) remains largely unexplored. Herein, we systematically investigated the V(V) reduction capabilities and underlying mechanisms of Bacillus megaterium R01, a S0RB strain isolated from the stone coal mining region. Under sulfur-depleted conditions, B. megaterium R01 demonstrated limited reduction capacity (<54.3% removal efficiency for 200 mg/L V(V)). In contrast, S0 supplementation enabled near-complete V(V) reduction (97.6 ± 2.1%) even at elevated concentrations (400 mg/L), achieving a relatively low carbon consumption rate (TOC/V(V) of ∼0.6). Sulfhydryl (SH) compounds, reaching 424.2 ± 9.9 μmol/L within 5 days, were likely crucial for reducing V(V) to V(IV). This mechanism differs from that of other V-reducing bacteria. The transcriptome analysis revealed that the up-regulation of genes associated with sulfur metabolism, cysteine, and methionine metabolism in B. megaterium R01 is likely to contribute to its enhanced resistance toward V(V). Additionally, the biosynthesis of intracellular BSH in B. megaterium R01, and the extracellular SH groups (e.g., Trx and TrxR encode enzymes) play an irreplaceable role in reducing V(V) by B. megaterium R01. This study enhances our understanding of V(V) reduction in sulfur-rich environments and suggests a promising approach for remediating V(V)-contaminated groundwater, sediments, and soils.