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Journal of Bacteriology, November 2007, p. 8145-8153, Vol. 189, No. 22
0021-9193/07/$08.00+0     doi:10.1128/JB.01017-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Dissection of the Caffeate Respiratory Chain in the Acetogen Acetobacterium woodii: Identification of an Rnf-Type NADH Dehydrogenase as a Potential Coupling Site{triangledown}

Frank Imkamp,1 Eva Biegel,1 Elamparithi Jayamani,2 Wolfgang Buckel,2 and Volker Müller1*

Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Max-von-Laue-Str. 9, 60438 Frankfurt, Germany,1 Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps University, 35032 Marburg, Germany2

Received 27 June 2007/ Accepted 2 September 2007

The anaerobic acetogenic bacterium Acetobacterium woodii couples caffeate reduction with electrons derived from hydrogen to the synthesis of ATP by a chemiosmotic mechanism with sodium ions as coupling ions, a process referred to as caffeate respiration. We addressed the nature of the hitherto unknown enzymatic activities involved in this process and their cellular localization. Cell extract of A. woodii catalyzes H2-dependent caffeate reduction. This reaction is strictly ATP dependent but can be activated also by acetyl coenzyme A (CoA), indicating that there is formation of caffeyl-CoA prior to reduction. Two-dimensional gel electrophoresis revealed proteins present only in caffeate-grown cells. Two proteins were identified by electrospray ionization-mass spectrometry/mass spectrometry, and the encoding genes were cloned. These proteins are very similar to subunits {alpha} (EtfA) and ß (EtfB) of electron transfer flavoproteins present in various anaerobic bacteria. Western blot analysis demonstrated that they are induced by caffeate and localized in the cytoplasm. Etf proteins are known electron carriers that shuttle electrons from NADH to different acceptors. Indeed, NADH was used as an electron donor for cytosolic caffeate reduction. Since the hydrogenase was soluble and used ferredoxin as an electron acceptor, the missing link was a ferredoxin:NAD+ oxidoreductase. This activity could be determined and, interestingly, was membrane bound. A search for genes that could encode this activity revealed DNA fragments encoding subunits C and D of a membrane-bound Rnf-type NADH dehydrogenase that is a potential Na+ pump. These data suggest the following electron transport chain: H2 -> ferredoxin -> NAD+ -> Etf -> caffeyl-CoA reductase. They also imply that the sodium motive step in the chain is the ferredoxin-dependent NAD+ reduction catalyzed by Rnf.

* Corresponding author. Mailing address: Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University of Frankfurt/Main, Max-von-Laue-Str. 9, 60438 Frankfurt, Germany. Phone: 49-69-79829507. Fax: 49-69-79829306. E-mail: vmueller{at}bio.uni-frankfurt.de

{triangledown} Published ahead of print on 14 September 2007.

Journal of Bacteriology, November 2007, p. 8145-8153, Vol. 189, No. 22
0021-9193/07/$08.00+0     doi:10.1128/JB.01017-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Schut, G. J., Adams, M. W. W. (2009). The Iron-Hydrogenase of Thermotoga maritima Utilizes Ferredoxin and NADH Synergistically: a New Perspective on Anaerobic Hydrogen Production. J. Bacteriol. 191: 4451-4457 [Abstract] [Full Text]  
  • Herrmann, G., Jayamani, E., Mai, G., Buckel, W. (2008). Energy Conservation via Electron-Transferring Flavoprotein in Anaerobic Bacteria. J. Bacteriol. 190: 784-791 [Full Text]  


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