Enterobacter kobei enables straw-driven V(V) bioreduction in wastewater at elevated V(V) concentrations: interfacial detoxification and electron-transfer pathways

Microbial reduction of pentavalent vanadium [V(V)] using lignocellulosic straw as a slow-release carbon source represents a promising strategy for treating V(V)-laden wastewater. However, current straw-driven V(V) reduction systems mainly rely on mixed consortia, and their metabolic complexity has hindered the elucidation of coupling mechanisms between straw degradation and V(V) reduction. In this study, we isolated Enterobacter kobei (E. kobei), which achieved 95-100% V(V) removal across 50-2200 mg L^-1 using wheat straw as the sole added carbon source and maintained stable performance in the presence of representative industrial wastewater constituents. Mechanistically, V(V) stress stimulated straw degradation and bioavailable organic carbon release, sustaining cellular metabolism and electron-donor supply, while the porous straw structure promoted bacterial colonization and extracellular polymeric substances (EPS)-rich biofilm formation. This biofilm interface created a microenvironment conducive to quinone-coupled, nitrate reductase (Nar)-associated membrane electron transfer and riboflavin-mediated extracellular electron transfer. Concurrently, quorum sensing enhanced EPS production and electron transfer, thereby synchronously coupling biofilm development with interfacial detoxification and extracellular V(V) reduction. Validation experiments with real industrial wastewater confirmed the effectiveness of this mechanism, demonstrating 96.07% V(V) removal at 1000 mg L⁻¹ and stable performance across three consecutive batch cycles. Overall, this work establishes a mechanistic framework for single-strain adaptation to V(V) stress and efficient V(V) removal, providing both a theoretical basis and practical guidance for the bioremediation of vanadium-laden industrial wastewater.