Chromate reduction and 16S rRNA identification of bacteria isolated from a Cr(VI)-contaminated site

Abstract.

A Gram-positive, hexavalent chromium [chromate: Cr(VI)]-tolerant bacterium, isolated from tannery waste from Pakistan, was identified as a Microbacterium sp. by 16S rRNA gene sequence homology. The strain (designated as MP30) reduced toxic Cr(VI) only under anaerobic conditions at the expense of acetate as the electron donor. The bacterium was able to grow aerobically in L-broth supplemented with 15 mM CrO₄ ^2– but then did not reduce Cr(VI). At a concentration of 2.4×10⁹ cells/ml, 100 µM sodium chromate was reduced within 30 h; however, the maximum specific reduction rate was obtained at lower initial cell concentrations.