Manganese Redox Cycling Promotes Microbial Vanadium Immobilization in Soil.

Although microbial reductive immobilization offers a promising means of treating toxic vanadium(V) in soil, the influence of ubiquitous manganese (Mn) in soil on V geochemistry is still poorly understood. This work demonstrates the significant impact of Mn redox cycling on microbial V immobilization. Positively correlated V and Mn contents in soil coaffected microbial communities. Both manganosite (MnO) and pyrolusite (MnO2) accelerated V(V) bioreduction to V(IV) as highly stable Mn oxovanadic compounds such as MnV2O5. Mn(II), Mn(III), and Mn(IV) were found, enabling Mn redox cycling, thus enhancing electron transfer for V(V) bioreduction. Two newly described species Bosea sp. and Rhodoferax sp. were putatively involved in V(V) reduction regulated by narG, napA, and nirK. Mn(II) oxidation by Bosea sp. harboring moxA and Mn(IV) reduction by Rhodoferax sp. possessing mtrC resulted in the production of Mn(III) intermediates, which took disproportionation spontaneously to Mn(II) and Mn(IV) again. Pure-culture tests provided genus-level metabolic support for these species. Field experiments confirmed the practical V immobilization effectiveness. This study provides insight into the biogeochemical interactions between V and Mn in soils and facilitates the development of new strategies for V bioremediation.