Microbial vanadate reduction: unveiling electron transfer and isotope fractionation

A recent study published in the journal Engineering has shed light on the microbial reduction of vanadate (V(V)), a crucial process in environmental geochemistry and vanadium detoxification. The research, conducted by Wenyue Yan, Baogang Zhang, Fang Huang and their colleagues, investigated the electron transfer pathways and vanadium isotope fractionation during this process.

Vanadium, a redox-sensitive metal, is widely distributed in the environment. High levels of vanadium can pose risks to human health and the ecosystem. Microbial reduction of V(V) to the less toxic V(IV) is an important detoxification strategy. However, the underlying mechanisms and associated isotope fractionation were not fully understood.

The researchers used two bacterial strains, Bacillus subtilis (Gram-positive) and Thauera humireducens (Gram-negative), which are commonly found in V-polluted sites. In a 10-day incubation experiment with an initial V(V) concentration of 50 mg/L, both strains effectively reduced V(V). B. subtilis removed (90.5%±1.6%) and T. humireducens removed (93.0%±1.8%) of V(V). The reduction product, insoluble V(IV), was distributed both inside and outside the cells.

Electron transfer played a critical role in V(V) reduction. Compounds such as cytochrome C, nicotinamide adenine dinucleotide (NADH), and glutathione were involved. Metabolomic analysis showed that metabolites like quinone, biotin, and riboflavin mediated electron transfer in both strains. These findings suggest multiple electron transfer pathways, including extracellular transfer by cytochrome C and soluble metabolites, and intracellular transfer by NADH and glutathione.

The study also focused on vanadium isotope fractionation. As V(V) bioreduction proceeded, the remaining aqueous V became isotopically heavier. The V isotope composition dynamics followed a Rayleigh fractionation model. The isotope enrichment factors were (–0.54‰±0.04‰) for B. subtilis and (–0.32‰±0.03‰) for T. humireducens, with no significant difference between the two strains. This indicates that lighter vanadium isotopes react preferentially during microbial-mediated V(V) reduction.

This research has several implications. It expands the list of V(V)-reducing microorganisms, providing potential candidates for bioremediation of V-polluted environments. Understanding the electron transfer pathways can help in developing more efficient strategies for vanadium detoxification. Moreover, the accurate assessment of V isotope fractionation during biochemical reactions can be used to identify pollution sources and trace pollution processes in the environment. However, the researchers note that further investigation is needed to understand the influence of other geochemical and hydrodynamic factors on V isotope fractionation. Overall, this study advances our understanding of vanadium biogeochemistry and provides valuable insights for future research and environmental applications.

The paper “Electron Transfer Pathways and Vanadium Isotope Fractionation During Microbially Mediated Vanadate Reduction,” authored by Wenyue Yan, Baogang Zhang, Yi’na Li, Jianping Lu, Yangmei Fei, Shungui Zhou, Hailiang Dong, Fang Huang. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.01.001. For more information about the Engineering, follow us on X (https://twitter.com/EngineeringJrnl) & like us on Facebook (https://www.facebook.com/EngineeringJrnl).