Anaerobic Biotransformation of High Concentrations of Chloroform by an Enrichment Culture and Two Bacterial Isolates

Abstract

A fermentative enrichment culture (designated DHM-1) was developed that is capable of cometabolically biotransforming high concentrations of chloroform (CF) to nontoxic end products. Two Pantoea spp. were isolated from DHM-1 that also possess this dechlorination capability. Following acclimation to increasing levels of CF, corn syrup-grown DHM-1 was able to transform over 500 mg/liter CF in the presence of vitamin B 12 (approximately 3% of CF on a molar basis) at a rate as high as 22 mg/liter/day in a mineral salts medium. CO, CO 2 , and organic acids were the predominant biodegradation products, suggesting that hydrolytic reactions predominate during CF transformation. DHM-1 was capable of growing on corn syrup in the presence of high concentrations of CF (as may be present near contaminant source zones in groundwater), which makes it a promising culture for bioaugmentation. Strains DHM-1B and DHM-1T transform CF at rates similar to that of the DHM-1 enrichment culture. The ability of these strains to grow in the presence of high concentrations of CF appears to be related to alteration of membrane fluidity or homeoviscous and homeophasic adaptation.Chloroform (CF) is a toxic organic compound that is frequently detected in groundwater. In the 2007 "CERCLA Priority List of Hazardous Substances," CF ranks eleventh overall and is the third highest among chlorinated organics after vinyl chloride and polychlorinated biphenyls (4). When present at hazardous waste sites, CF is often a focal point for evaluating the feasibility of bioremediation, since it is toxic to many obligate anaerobic prokaryotes (44). For example, 1 mg/liter of CF completely inhibited dechlorination of tetrachloroethene (PCE) by a chlororespiring anaerobic isolate (32). Inhibition of reductive dechlorination of chloroethenes by CF is a general problem for sites cocontaminated with CF, which can only be overcome by first removing the CF (6).In spite of major recent advances in bioremediation of chlorinated organic compounds, treatment of CF, especially at high concentrations (e.g., Ͼ100 mg/liter), remains challenging. Although aerobic biotransformation of CF is possible (e.g., cometabolism by a butane-grown strain) (14), CF is more difficult to cometabolize than trichloroethene (42). Biotransformation of CF by mixed or pure cultures under methanogenic (5, 21) and sulfate-reducing (20) conditions has been reported, however, only at low-mg/liter CF concentrations.Corrinoids such as vitamin B 12 (i.e., cyanocobalamin) are effective catalysts for increasing the rate of halomethane biotransformation under anaerobic conditions. Addition of vitamin B 12 also shifts the pathway away from reductive dechlorination and toward hydrolytic and substitutive reactions, forming CO, CO 2 , and organic acids as the major products (8,23,24). With low levels of B 12 added (3 to 5% molar ratios of CF), an enrichment culture grown on dichloromethane (DCM) as the sole substrate (8) and a lactate-grown sulfate-reducing enrichment culture (18) were able to biotransform up ...

Metagenomic- and cultivation-based exploration of anaerobic chloroform biotransformation in hypersaline sediments as natural source of chloromethanes

“…CF is persistent in the environment and is hardly dechlorinated/degraded under oxic conditions due to the three chlorine substitutes (17, 18). In contrast, microbial CF transformation is often mediated by anaerobic microbes (19–23). Anaerobic CF transformation has been reported to be mediated by acetogens like Acetobacterium woodii (24) and Clostridium sp.…”

“…(26–28), and fermentative Pantoea spp. (23) producing dichloromethane (DCM), carbon monoxide (CO) and/or carbon dioxide (CO 2 ). This is a co-metabolic process for which the responsible genes and enzymes are not yet clear.…”

Electron‐acceptor loadings affect chloroform dechlorination in a hydrogen‐based membrane biofilm reactor

“…Successful anaerobic biodegradation of CF requires sufficient amounts of electron donor and a carbon source that can be used by the CF‐reducing bacteria (Bouwer, Rittmann, & McCarty, ; Cappelletti, Frascari, Zannoni, & Fedi, ; Chung & Rittmann, ; Grostern, Duhamel, Dworatzek, & Edwards, ; Lee et al, ; Shan, Kurtz, Mykytczuk, Trevors, & Freedman, ). Complete CF biodegradation also can occur in aerobic conditions, but it relies on a cometabolic pathway that requires a cosubstrate, dissolved O 2 , and a monooxygenase (Cappelletti et al, ; Rittmann & McCarty, ).…”

“…2007; Grostern, Duhamel, Dworatzek, & Edwards, 2010;Lee et al, 2012;Shan, Kurtz, Mykytczuk, Trevors, & Freedman, 2010).…”

“…strain Y51 are well-known for respiring chlorinated compounds, but they also can respire NO 3 − and SO 4 2− (Achenbach, Michaelidou, Bruce, Fryman, & Coates, 2001;Salinero et al, 2009;Suyama et al, 2001). In addition, homoacetogens using H 2 as the electron donor and synthesizing acetate may be involved with hydrolytic dechlorination of CF (Egli, Stromeyer, Cook, & Leisinger, 1990;Egli, Tschan, Scholtz, Cook, & Leisinger, 1988;Freedman & Gossett, 1991;Shan et al, 2010).…”