Acetogenesis from dichloromethane by a two-component mixed culture comprising a novel bacterium

Abstract

A strictly anaerobic two-component culture able to grow exponentially with a doubling time of 20 h on a medium containing dichloromethane as the carbon and energy source was characterized. On a medium without sulfate, we observed (per mol of dichloromethane) a mass balance of 2 mol of chloride, 0.26 mol of acetate, 0.05 mol of formate, and 0.25 mol of carbon in biomass. One component of the culture, strain DMB, was identified by a 16S ribosomal DNA analysis as a Desulfovibrio sp. The other component, the gram-positive organism strain DMC, could not be isolated. It was possible, however, to associate strain DMC on a medium containing dichloromethane in a coculture with Acetobacterium woodii or Methanospirillum hungatei. Coculture of strain DMC with the Archaeon M. hungatei allowed us to specifically amplify by PCR the 16S rRNA gene of strain DMC. A phylogenetic analysis of the 16S ribosomal DNA sequence revealed that this organism groups within the radiation of the Clostridium-Bacillus subphylum and exhibits the highest levels of sequence similarity (89%) with Desulfotomaculum orientis and Desulfitobacterium dehalogenans. Since the novel organism strain DMC was able to grow acetogenically with dichloromethane when it was associated with one of three metabolically different partners and since, in contrast to strain DMB, strain DMC contained carbon monoxide dehydrogenase activity, this bacterium is responsible for both the dehalogenation of dichloromethane and the acetogenesis observed in the original two-component culture. The obligatory dependence of strain DMC on a partner during growth with dichloromethane is thought to stem from the need for a growth factor produced by the associated organism.

Rapid Consumption of Low Concentrations of Methyl Bromide by Soil Bacteria

“…MeBr uptake was generally an aerobic process which did not occur significantly during anaerobic incubations, including those in which excess H 2 and CO 2 were added. Methyl halides can be used by anaerobic bacteria, including acetogens (10,12) and methanogens (17), and anaerobic sediments are capable of using MeBr (17). Oremland et al (16) suggested that anaerobic bacteria in soils may be significant consumers of MeBr but were unable to detect any role of methanogens or acetogens.…”

Determination of microbial diversity in environmental samples: pitfalls of PCR-based rRNA analysis

“…For almost all analyses of microbial ecosystems ampli¢ed 16S rRNA genes have to be separated prior to subsequent sequencing and/or hybridization as they constitute a heterogeneous mixture of sequences. Exceptions are`one-species' microbial communities like the highly speci¢c symbiosis between a sulfur-oxidizing bacterium and a marine nematode [16] and co-cultures of two microorganisms of di¡erent kingdoms (Bacteria and Archaea), which allowed speci¢c PCR ampli¢cation [109].…”

Determination of microbial diversity in environmental samples: pitfalls of PCR-based rRNA analysis

“…For almost all analyses of microbial ecosystems amplified 16S rRNA genes have to be separated prior to subsequent sequencing and/or hybridization as they constitute a heterogeneous mixture of sequences. Exceptions are ‘one‐species’ microbial communities like the highly specific symbiosis between a sulfur‐oxidizing bacterium and a marine nematode [16]and co‐cultures of two microorganisms of different kingdoms ( Bacteria and Archaea ), which allowed specific PCR amplification [109].…”