Electron transfer of microbial V(Ⅴ)reduction and its effects on algae growth
To explore the mechanism of microbial V(Ⅴ)reduction,a strain of Enterobacter kobei NC1-2 was isolated from vanadium-contaminated soil to investigate the effects of different electron transfer inhibitors and electron shuttles on the electron transfer process of V(Ⅴ)reduction,as well as the changes in toxicity before and after microbial V(Ⅴ)reduction and its effects on algal growth.The results showed that the reduction rate of V(Ⅴ)by strain NC1-2 was 90.26%after 3 d of incubation at an initial V(Ⅴ)concentration of 20 mg·L-1.Scanning electron microscopy showed that amorphous materials were attached to the surface of the strain,which was confirmed to contain vanadium by energy-scattering X-ray spectroscopy.Additionally,X-ray photoelectron spectroscopy analysis indicated that strain NC1-2 reduced V(Ⅴ)to V(Ⅳ).Furthermore,the reduction of V(Ⅴ)by strain NC1-2 was inhibited by the electron inhibitors capsaicin,quinacrine,and copper chloride.Conversely,riboflavin,acting as an electron shuttle,shortened the electron transfer distance and promoted extracellular electron transfer,thus facilitating the reduction of V(Ⅴ)by strain NC1-2.The toxicity of V(Ⅴ)decreased after its reduction to V(Ⅳ),resulting in reduced growth stress to Chlorella pyrenoidosa and Scenedesmus obliquus.Both algal species exhibited a significant increase in algal density after 96 h of growth and in chlorophyll a content at 17.4 and 15.8 mg·L-1,respectively.This study demonstrates that enhanced microbial reduction of V(Ⅴ)reduces its toxicity to aquatic organisms.
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