Metabolism of Dichloromethane by the Strict Anaerobe Dehalobacterium formicoaceticum

116

Chloroform (CF), or trichloromethane, is an ubiquitous environmental pollutant because of its widespread industrial use, historically poor disposal and recalcitrance to biodegradation. Chloroform is a potent inhibitor of metabolism and no known organism uses it as a growth substrate. We discovered that CF was rapidly and sustainably dechlorinated in the course of investigating anaerobic reductive dechlorination of 1,1,1-trichloroethane in a Dehalobacter-containing culture. Like 1,1,1-trichloroethane dechlorination in this culture, CF dechlorination was a growth-linked respiratory process, requiring H(2) as an electron donor and CF as an electron acceptor. Moreover, the same specific reductive dehalogenase likely catalyzed both reactions. This Dehalobacter population appears specialized for substrates with three halogen substituents on the same carbon atom, with widespread implications for bioremediation.

Section: Resultsmentioning

confidence: 99%

Chloroform respiration to dichloromethane by a Dehalobacter population

Grostern

Duhamel

Dworatzek³

et al. 2010

116

“…Formate was observed at very low levels and did not accumulate, suggesting its rapid oxidation to CO2 and H2. It has been demonstrated that DCM fermenting bacteria, in particular D. formicoaceticum, can produce formate and acetate directly from DCM (Mägli et al, 1998). In D. formicoaceticum DCM is directly inserted into the methyl group of acetate, the carboxyl group being derived from CO2 from culture medium.…”

Section: Chmentioning

confidence: 99%

“…The only bacterium in pure culture that utilizes DCM as the sole carbon and energy source under anaerobic conditions is Dehalobacterium formicoaceticum (Mägli et al, 1996). Experiments with 14 C-labelled DCM showed this organism fermented DCM to formate and acetate (Mägli et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Complete chloroform dechlorination by organochlorine respiration and fermentation

Lee¹,

Low²,

Zemb³

et al. 2011

101

109

Chloroform (CF, CHCl(3)) is a recalcitrant and toxic environmental pollutant. In this communication we report for the first time a microbial community capable of complete CF dechlorination by metabolic processes. Cultures derived from subsurface soil (3.5 m) could sustain complete dechlorination of CF at levels of least 360 µM at a rate of 40 µM per day. Scrutiny of CF dechlorination revealed two metabolic processes at work. First, CF was respired to dichloromethane (DCM, CH(2) Cl(2)), which was then fermented to acetate, hydrogen and carbon dioxide. Elevated hydrogen partial pressures were found to inhibit the fermentation process. Interspecies hydrogen transfer was observed in the form of methanogenesis and acetogenesis. This suggests that the dechlorination process required syntrophic partners to maintain low hydrogen partial pressures. (13)C-labelled DCM was employed to help elucidate the chemistry of the process and identify bacterial community members involved. CF respiring cultures, where emulsified vegetable oil was supplied as the electron donor and DCM fermenting cultures, where DCM was supplied as the sole organic carbon source were studied separately. Pyrosequencing of these cultures revealed Dehalobacter lineages as a predominant community member in both. Subsequent growth experiments confirmed that the proliferation of Dehalobacter was linked directly to both the dehalorespiration and dehalofermentation processes.

“…In contrast to chlorinated ethenes, chlorinated ethanes and chloroform, DCM and CM do not undergo direct hydrogenolysis (i.e., reductive dechlorination). Instead, based on physiological and biochemical evidence, DCM and CM are funnelled into the Wood-Ljungdahl pathway (reductive acetyl-CoA pathway) after chlorine removal and broken down to acetate, formate, carbon dioxide and inorganic chloride (Meßmer et al, 1993;M€ agli et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Mutualistic interaction between dichloromethane‐ and chloromethane‐degrading bacteria in an anaerobic mixed culture

Gao

Kleindienst

Griffiths

et al. 2017

The microbial mixed culture RM grows with dichloromethane (DCM) as the sole energy source generating acetate, methane, chloride and biomass as products. Chloromethane (CM) was not an intermediate during DCM utilization consistent with the observation that CM could not replace DCM as a growth substrate. Interestingly, cultures that received DCM and CM together degraded both compounds concomitantly. Transient hydrogen (H ) formation reaching a maximum concentration of 205 ± 13 ppmv was observed in cultures growing with DCM, and the addition of exogenous H at concentrations exceeding 3000 ppmv impeded DCM degradation. In contrast, CM degradation in culture RM had a strict requirement for H . Following five consecutive transfers on CM and H , Acetobacterium 16S rRNA gene sequences dominated the culture and the DCM-degrader Candidatus Dichloromethanomonas elyunquensis was eliminated, consistent with the observation that the culture lost the ability to degrade DCM. These findings demonstrate that culture RM harbours different populations responsible for anaerobic DCM and CM metabolism, and further imply that the DCM and CM degradation pathways are mechanistically distinct. H generated during DCM degradation is consumed by the hydrogenotrophic CM degrader, or may fuel other hydrogenotrophic processes, including organohalide respiration, methanogenesis and H /CO reductive acetogenesis.