MICROBIAL REDUCTION OF VITAMIN-B-12 BY SHEWANELLA-ALGA STRAIN BRY WITH SUBSEQUENT TRANSFORMATION OF CARBON-TETRACHLORIDE

The ability of a metal-reducing bacterium to microbially reduce vitami n 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 cataly zed by this microbially-reduced vitamin B-12 was then evaluated. When incubated in the presence of Shewanella alga strain Cry and an electro n donor, the microbial reduction of vitamin B-12a to B-12r was observe d as a shift in the vitamin B-12 spectrum. In treatments containing vi tamin B-12 and an electron donor but without Cry, the predominant spec ies was vitamin B-12a. The introduction of BrY into the system resulte d in the production of vitamin B-12r. The transformation of carbon tet rachloride (CT), chloroform (CF), and dichloromethane (DCM) was examin ed in batch systems containing vitamin B-12, Shewanella alga strain Cr y, and an electron donor. Transformation of both CT and CF was observe d, while no significant change in the DCM concentration was detected. Carbon monoxide was the major product of CT transformation. No signifi cant transformation of CT or CF was detected when vitamin B-12 was Omi tted from the system. This work demonstrates that a metal-reducing bac terium, with no apparent ability to transform CT or CF directly, media tes the reduction of vitamin B-12, which in turn catalyzes the transfo rmation of CT.