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

Abstract

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.

Proteogenomics Reveals Novel Reductive Dehalogenases and Methyltransferases Expressed during Anaerobic Dichloromethane Metabolism

“…The expression of methyltransferases, WLP enzymes, and two RDases provided information for proposing possible DCM degradation pathways in "Candidatus Dichloromethanomonas elyunquensis" strain RM. Strain RM, the DCM degrader in the microbial consortium RM, requires DCM as a growth substrate (14,16). The consumption of DCM by strain RM yielded 2.6 ϫ 10 7 Ϯ 0.5 ϫ 10 7 cells per mol Clreleased, with a doubling time of around 4.6 days for strain RM (14).…”

“…Assuming an initial reductive dechlorination step, the first DCM metabolite would be chloromethane (CM); however, CM production was never observed in consortium RM (12,14,16). While it is possible that CM is rapidly consumed or remains enzymebound, thus evading detection, such scenarios are not supported by experimental data because strain RM did not grow with CM (16). Thus, reductive dechlorination of DCM to CM is unlikely, and DCM does not appear to be the substrate for the expressed RDases.…”

“…Hydrogen was measured with a Peak Performer 1 reducing compound photometer (Peak Laboratories, Mountain View, CA). Formate and acetate were quantified with an Agilent 1200 series HPLC system as described previously (16).…”

Use of dual element isotope analysis and microcosm studies to determine the origin and potential anaerobic biodegradation of dichloromethane in two multi-contaminated aquifers

“…Recently, mixed bacterial cultures containing Dehalobacter sp. and/or D. elyunquensis have been reported to ferment DCM to mainly acetate (Chen et al, 2017;Justicia-Leon et al, 2012;Kleindienst et al, 2017;Lee et al, 2015Lee et al, , 2012.…”

Use of C–Cl CSIA to elucidate origin and fate of DCM in complex contaminated field sites

“…and/or Dehalobacterium sp. [4][5][6], and a new bacterium identified as Candidatus Dichloromethanomonas elyunquensis [7,8].…”