Microbial Reduction of Vitamin B12 by Shewanella alga Strain BrY with Subsequent Transformation of Carbon Tetrachloride

Abstract

The ability of a metal-reducing bacterium to microbially reduce vitamin B12 was determined to expand our understanding of the role vitamin B12 plays in the transformation of halogenated compounds in microbial systems. The subsequent transformation of chlorinated methanes catalyzed by this microbially-reduced vitamin B12 was then evaluated. When incubated in the presence of Shewanella alga strain BrY and an electron donor, the microbial reduction of vitamin B12a to B12r was observed as a shift in the vitamin B12 spectrum. In treatments containing vitamin B12 and an electron donor but without BrY, the predominant species was vitamin B12a. The introduction of BrY into the system resulted in the production of vitamin B12r. The transformation of carbon tetrachloride (CT), chloroform (CF), and dichloromethane (DCM) was examined in batch systems containing vitamin B12, Shewanella alga strain BrY, and an electron donor. Transformation of both CT and CF was observed, while no significant change in the DCM concentra tion was detected. Carbon monoxide was the major product of CT transformation. No significant transformation of CT or CF was detected when vitamin B12 was omitted from the system. This work demonstrates that a metal-reducing bacterium, with no apparent ability to transform CT or CF directly, mediates the reduction of vitamin B12, which in turn catalyzes the transformation of CT.