Carbon Tetrachloride Degradation:  Effect of Microbial Growth Substrate and Vitamin B₁₂ Content

Abstract

Microbial degradation kinetics of carbon tetrachloride (CT) under reducing conditions were investigated for different cultures, fed with 1,2-propanediol, dextrose, propionaldehyde, or acetate and nitrate, in the anaerobic step of an anaerobic/aerobic operation sequence. Methanogenesis was inhibited due to the aerobic step. CT biodegradation rates followed first-order kinetics with respect to CT concentration and biomass and were not affected by the presence of growth substrate. CT degradation rates increased linearly with higher intracellular vitamin B12 content. The culture fed 1,2-propanediol had the highest vitamin B12 content, which was 3.8, 4.7, and 16 times that of the propionaldehyde-, dextrose-, and acetate-fed cultures, respectively, and its first-order degradation rate constant was 2.8, 4.5, 6.0 times that for those cultures, respectively. No CT degradation occurred with culture liquid, suggesting that intracellular factors were responsible for CT degradation. The propanediol culture was able to sustain a constant CT degradation rate for a 16-day test period without substrate addition. Compared to a propanediol-fed culture grown only under anaerobic conditions, the propanediol culture grown under the sequential anaerobic/aerobic condition resulted in more biomass growth and a greater CT degradation rate per unit of propanediol fed, although its CT degradation rate per unit of biomass was lower.

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

“…The molar ratios used in this study were far lower than those evaluated previously. Zou et al (2000) observed 3-to 7-fold enhancement of CT degradation kinetics in enrichment cultures developed from anaerobic digester sludge with a molar ratio 2.3 CNB12:CT. A 10-fold increase in CT degradation rates was observed in DCM-enrichment cultures when a molar ratio of 0.1 CNB12:CT was applied (Hashsham et al 1995). A 30-fold enhancement in CT degradation rates were observed in pure cultures of the acetogenic bacterium, Acetobacterium woodii, when a molar ratio of 0.11 HOB12:CT was applied (Hashsham & Freedman 1999).…”

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

“…The first steps in the metabolism of these substrates in many enteric bacteria involve, propanediol dehydratase, glycerol dehydratase and ethanolamine ammonia lyase; respectively, which are all adenosylcobalamin-dependent enzymes. The substrate, 1,2-propanediol has been used to stimulate vitamin B 12 production in methanogenic enrichment cultures (Zou et al 2000). These enrichment cultures were able to degrade CT, and the rates of CT-degradation rates were found to be proportional to intracellular levels of vitamin B 12 .…”

“…The first step in the catabolism is the conversion of 1,2-propanediol to propionaldehyde which is dependent on vitamin B 12 and thus the presence of 1,2-propanediol induces vitamin B 12 biosynthesis (Roth et al 1996). The use of 1,2-propanediol as a growth substrate stimulated vitamin B 12 production in an enrichment culture cycled between anaerobic/aerobic conditions, The increased vitamin B 12 production was correlated with increased rates of CT degradation (Zou et al 2000).…”

Effects of various environmental conditions on the transformation of chlorinated solvents by Methanosarcina thermophila cell exudates

“…An alternative to maintaining and stimulating microbes in situ is the injection of microbiologically produced cofactors that are capable of dechlorinating these compounds. Researchers have found several cofactors (heme, vitamin B 12 , cofactor F 430 ) that can degrade CT, CF, and TCE (Burris et al, 1996;Buschman et al, 1999;Chiu and Reinhard, 1996;Gantzer and Wackett, 1991;Lin et al, 1989;Marks et al, 1989;Mazumder et al,1987;Mowder et al, 2000;Public Health Laboratory Service Board, 1989;Zou et al, 2000).…”