Mineralization versus fermentation: evidence for two distinct anaerobic bacterial degradation pathways for dichloromethane

• Published in: The ISME Journal 2020-04, Vol.14 (4), p.959-970
• Main Authors: Chen, Gao, Fisch, Alexander R., Gibson, Caleb M., Erin Mack, E., Seger, Edward S., Campagna, Shawn R., Löffler, Frank E.
• Format: Article
• Language: English
• Subjects: 631/326/171; 704/172; 82/16; 82/58; 82/6; Acetates - metabolism; Acetic acid; Anaerobiosis; Anoxic conditions; Anthropogenic factors; Bacteria, Anaerobic - metabolism; BASIC BIOLOGICAL SCIENCES; Biodegradation; Biodegradation, Environmental; Biomedical and Life Sciences; Carbon - metabolism; Carbon dioxide; Carbon Dioxide - metabolism; Culture; Dichloromethane; Ecology; Euryarchaeota - metabolism; Evolutionary Biology; Fermentation; Free energy; Gas chromatography; Hydrogen - metabolism; Life Sciences; Mass spectrometry; Mass spectroscopy; Metabolites; Methane - metabolism; Methylene Chloride - chemistry; Methylene Chloride - metabolism; Microbial Ecology; Microbial Genetics and Genomics; Microbiology; Mineralization; Mixed culture; NMR; Nuclear magnetic resonance; Peptococcaceae - metabolism; Pollutants; Pure culture
• ISSN: 1751-7362; 1751-7370
• DOI: 10.1038/s41396-019-0579-5

Dichloromethane (DCM) is an anthropogenic pollutant with ozone destruction potential that is also formed naturally. Under anoxic conditions, fermentation of DCM to acetate and formate has been reported in axenic culture Dehalobacterium formicoaceticum , and to acetate, H 2 and CO 2 in mixed culture RM, which harbors the DCM degrader ‘ Candidatus Dichloromethanomonas elyunquensis’. RM cultures produced 28.1 ± 2.3 μmol of acetate from 155.6 ± 9.3 μmol DCM, far less than the one third (i.e., about 51.9 µmol) predicted based on the assumed fermentation model, and observed in cultures of Dehalobacterium formicoaceticum . Temporal metabolite analyses using gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectroscopy revealed that no 13 C-labeled acetate was formed in 13 C-DCM-grown RM cultures, indicating acetate was not a direct product of DCM metabolism. The data were reconciled with DCM mineralization and H 2 consumption via CO 2 reduction to acetate and methane by homoacetogenic and methanogenic partner populations, respectively. In contrast, Dehalobacterium formicoaceticum produced 13 C-labeled acetate and formate from 13 C-DCM, consistent with a fermentation pathway. Free energy change calculations predicted that organisms with the mineralization pathway are the dominant DCM consumers in environments with H 2