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

Abstract

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, H₂ and CO₂ 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 ¹³C-labeled acetate was formed in ¹³C-DCM-grown RM cultures, indicating acetate was not a direct product of DCM metabolism. The data were reconciled with DCM mineralization and H₂ consumption via CO₂ reduction to acetate and methane by homoacetogenic and methanogenic partner populations, respectively. In contrast, Dehalobacterium formicoaceticum produced ¹³C-labeled acetate and formate from ¹³C-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 H₂ <100 ppmv. These findings have implications for carbon and electron flow in environments where DCMmore » is introduced through natural production processes or anthropogenic activities.« less

Authors:

Chen, Gao ^[1]; Fisch, Alexander R. ^[2]; Gibson, Caleb M. ^[2]; Erin Mack, E. ^[3]; Seger, Edward S. ^[4]; Campagna, Shawn R. ^[2]; Löffler, Frank E.  ^[5]

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+ Show Author Affiliations

1. Univ. of Tennessee, Knoxville, TN (United States). Center for Environmental Biotechnology and Dept. of Civil and Environmental Engineering
2. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry
3. Corteva Agriscience, Wilmington, DE (United States)
4. The Chemours Company, Wilmington, DE (United States). Chemours Corporate Remediation Group
5. Univ. of Tennessee, Knoxville, TN (United States). Center for Environmental Biotechnology, Dept. of Civil and Environmental Engineering, Dept. of Chemistry, Dept. of Microbiology, and Dept. of Biosystems; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Joint Institute for Computational Sciences (JIBS)

Publication Date:

Mon Jan 06 00:00:00 EST 2020

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1606041

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

The ISME Journal

Additional Journal Information:

Journal Volume: 14; Journal Issue: 4; Journal ID: ISSN 1751-7362

Publisher:

Nature Publishing Group

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES