Efficient selenite reduction and chromium resistance by multiple pathways in Bacillus wiedmannii ES2-45 and Se-biofortification in rice by foliar application

Microbial selenite (Se(IV)) reduction to elemental selenium nanoparticles (SeNPs) and chromate (Cr(VI)) remediation constitute effective detoxification processes. The strain Bacillus wiedmannii ES2-45 can efficiently reduce 5 mmol/L Se(IV) into SeNPs over 14 h and 1 mmol/L Cr(VI) within 36 h. Proteomic analysis and qRT-PCR revealed that reductases, including dithiol oxidoreductase (DsbA), Fe-S biosynthesis domain-containing protein (Fes), and aldose-6-phosphate reductase (Aldo), and bacillithiol (BSH) were involved in Se(IV) reduction. Heterologous expression further confirmed the Se(IV)-reducing function of three genes and enhanced the Se(IV) and Cr(VI) resistance ability. Moreover, the difference between Se(IV) treatments and controls both intra- and extra- cellular BSH concentration per biomass indicated that BSH contributes to Se(IV) reduction. Selenium-fortified rice was obtained by foliar spray of SeNPs synthesized by the strain ES2-45. To the best of our knowledge, DsbA and Aldo reductase were firstly verified for the role in Se(IV) reduction and Cr(VI) resistance. Importantly, it is a promising strategy that B. wiedmannii ES2-45 is served as an efficient bacterium for SeNP synthesis, selenium biofortification and heavy metal bioremediation.