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  Energy conservation associated with ethanol formation from H2 and CO2 in Clostridium autoethanogenum involving electron bifurcation

Mock, J., Zheng, Y., Mueller, A., Ly, S., Tran, L., Segovia, S., et al. (2015). Energy conservation associated with ethanol formation from H2 and CO2 in Clostridium autoethanogenum involving electron bifurcation. Journal of Bacteriology, 197(18), 2965-2980. doi:10.1128/jb.00399-15.

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https://doi.org/10.1128/jb.00399-15 (Publisher version)
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 Creators:
Mock, J.1, Author           
Zheng, Y.2, Author           
Mueller, A., Author
Ly, S., Author
Tran, L., Author
Segovia, S., Author
Nagaraju, S., Author
Kopke, M., Author
Durre, P., Author
Thauer, R.2, Author           
Affiliations:
1Department of Biochemistry, Alumni, Max Planck Institute for Terrestrial Microbiology, Max Planck Society, ou_3266311              
2Emeriti Biochemistry of Anaerobic Microorganisms, Max Planck Institute for Terrestrial Microbiology, Max Planck Society, ou_3266289              

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 Abstract: Most acetogens can reduce CO2 with H-2 to acetic acid via the Wood-Ljungdahl pathway, in which the ATP required for formate activation is regenerated in the acetate kinase reaction. However, a few acetogens, such as Clostridium autoethanogenum, Clostridium ljungdahlii, and Clostridium ragsdalei, also form large amounts of ethanol from CO2 and H-2. How these anaerobes with a growth pH optimum near 5 conserve energy has remained elusive. We investigated this question by determining the specific activities and cofactor specificities of all relevant oxidoreductases in cell extracts of H-2/CO2-grown C. autoethanogenum. The activity studies were backed up by transcriptional and mutational analyses. Most notably, despite the presence of six hydrogenase systems of various types encoded in the genome, the cells appear to contain only one active hydrogenase. The active [FeFe]-hydrogenase is electron bifurcating, with ferredoxin and NADP as the two electron acceptors. Consistently, most of the other active oxidoreductases rely on either reduced ferredoxin and/or NADPH as the electron donor. An exception is ethanol dehydrogenase, which was found to be NAD specific. Methylenetetrahydrofolate reductase activity could only be demonstrated with artificial electron donors. Key to the understanding of this energy metabolism is the presence of membrane-associated reduced ferredoxin:NAD(+) oxidoreductase (Rnf), of electron-bifurcating and ferredoxin-dependent transhydrogenase (Nfn), and of acetaldehyde: ferredoxin oxidoreductase, which is present with very high specific activities in H-2/CO2-grown cells. Based on these findings and on thermodynamic considerations, we propose metabolic schemes that allow, depending on the H-2 partial pressure, the chemiosmotic synthesis of 0.14 to 1.5 mol ATP per mol ethanol synthesized from CO2 and H-2.

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Language(s): eng - English
 Dates: 2015-09
 Publication Status: Issued
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: eDoc: 717075
ISI: 000360712700008
DOI: 10.1128/jb.00399-15
 Degree: -

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Title: Journal of Bacteriology
  Other : J. Bacteriol.
Source Genre: Journal
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Publ. Info: Washington, DC : American Society for Microbiology (ASM)
Pages: - Volume / Issue: 197 (18) Sequence Number: - Start / End Page: 2965 - 2980 Identifier: ISSN: 0021-9193
CoNE: https://pure.mpg.de/cone/journals/resource/954925410823