A Bacillus subtilis strain can reduce hexavalent chromium to trivalent and an nfrA gene is involved

• Chromate-reducing bacteria were isolated from rare-earth ore in Baiyin for the first time.
• The isolated BYCr-1 shows high tolerance towards Cr (VI) (10 mM).
• NfrA was proved involving in chromate reduction.
• NfrA was transferred into E. coli BL21(DE3) to enhance its chromate-reducing ability.
• BYCr-1 can be used to bioremediate local chromate pollution.

Baiyin city, which is located upstream of the Yellow River and in the central part of Gansu province, China, is severely contaminated by heavy metals such as chromium. A Gram-positive bacterium BYCr-1 capable of reducing hexavalent chromium (Cr(VI)) to trivalent (Cr(III)) aerobically was isolated from a rare-earth ore in Baiyin, Gansu, China. 16S rRNA analysis revealed that it was closely related to Bacillus subtilis. It can reduce 0.2 mM Cr(VI) to Cr(III) in M9 medium after 48 h incubation. Transmission electron microscopy (TEM) image showed that Cr(III) precipitates were located both inside and outside the cells. An nfrA gene was upregulated by 5.3 folds upon Cr(VI) treatment. Furthermore, E. coli-NfrA demonstrated elevated chromate-reducing ability. Our results indicate that BYCr-1 is able to resist and reduce high concentrations of Cr(VI), which makes it a potentially suitable candidate for bioremediation of Cr(VI) contamination. This study also reveals that nfrA confers Cr(VI)-reducing ability in Bacillus subtilis.