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.

Enhancement of anaerobic carbon tetrachloride biotransformation in methanogenic sludge with redox active vitamins

“…The results taken as a whole from this study, indicate that reductive hydrogenolysis was a minor pathway; whereas substitutive reactions was the major pathway in cobalamin supplemented cultures. To support this hypothesis, the chemical reaction of biologically reduced CNB12 with CT resulted in CO as the major product (92%); whereas CF was a minor product (1.4%) (Workman et al 1997). In active methanogenic consortia CO would be further converted to CH 4 , acetate and CO 2 (Sipma et al 2003).…”

“…Oxidized cobalamins occur in the Co(III) state and can be reduced to the Co(II) and Co(I) states with standard reduction potentials at pH 7 (E 00 ) versus the standard hydrogen electrode (SHE) of 0.20 and À0.61 V for the couples Co(III)/Co(II) and Co(II)/Co(I), respectively (Lexa & Saveant 1983). The iron reducing bacterium, Shewanella alga strain BrY was shown to reduce cobalamin Co(III) to cobalamin Co(II) when provided with an adequate electron donor such as lactate or H 2 (Workman et al 1997). Similarly the reduction was also catalyzed by Salmonella enterica strain serovar Typhimurium LT2.…”

“…Cobalamin Co(II) prepared biologically with S. alga strain BrY was shown to effectively reduce CT in cell free systemswhile becoming oxidized to cobalamin Co(III) (Workman et al 1997). A reaction proceeding via CF would be energetically favorable with E 00 values 0.20 and 0.67 for the redox couples cobalamin Co(III)/cobalamin Co(II) and CF/CT (McCormick et al 2002), respectively.…”

Enhanced anaerobic biotransformation of carbon tetrachloride with precursors of vitamin B12 biosynthesis

“…Oxidized cobalamins occur in the Co(III) state and can potentially be reduced to the Co(II) and Co(I) states with standard reduction potentials at pH 7 (E¢ 0 ) versus the standard hydrogen electrode (SHE) of 0.20 and )0.61 V for the couples Co(III)/ Co(II) and Co(II)/Co(I), respectively (Lexa & Saveant 1983). The iron reducing bacterium, Shewanella alga strain BrY was shown to reduce cobalamin Co(III) to cobalamin Co(II) when provided with an adequate electron donor such as lactate or H 2 (Workman et al 1997). Similarly the reduction was also catalyzed by Salmonella enterica strain serovar Typhimurium LT2.…”

Microbial Transformations at Aqueous-Solid Phase Interfaces: A Bioremediation Approach

“…-Workman et al [155] studied CT dechlorination by an iron-reducing microbial culture amended with vitamin B 12 . They found that the culture reduced cobalt(III) in vitamin B 12 to cobalt(II), and that the reduced vitamin B 12 carried out CT dechlorination.…”