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

The ability of a metal-reducing bacterium to microbially reduce vitamin B 12 was determined to expand our understanding of the role vitamin B 12 plays in the transformation of halogenated compounds in microbial systems. The subsequent transformation of chlorinated methanes catalyzed by this microbially-reduced vitamin B 12 was then evaluated. When incubated in the presence of Shewanella alga strain BrY and an electron donor, the microbial reduction of vitamin B 12a to B 12r was observed as a shift in the vitamin B 12 spectrum. In treatments containing vitamin B 12 and an electron donor but without BrY, the predominant species was vitamin B 12a . The introduction of BrY into the system resulted in the production of vitamin B 12r . The transformation of carbon tetrachloride (CT), chloroform (CF), and dichloromethane (DCM) was examined in batch systems containing vitamin B 12 , Shewanella alga strain BrY, and an electron donor. Transformation of both CT and CF was observed, while no significant change in the DCM concentration was detected. Carbon monoxide was the major product of CT transformation. No significant transformation of CT or CF was detected when vitamin B 12 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 B 12 , which in turn catalyzes the transformation of CT.