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Journal of Bacteriology, June 2002, p. 3114-3121, Vol. 184, No. 11
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.11.3114-3121.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Functional Role for a 2-Oxo Acid Dehydrogenase in the Halophilic Archaeon Haloferax volcanii

Christian Wanner and Jörg Soppa*

Biozentrum Niederursel, Goethe University, D-60439 Frankfurt, Germany

Received 19 October 2001/ Accepted 15 March 2002

The archaeon Haloferax volcanii was previously shown to contain and transcribe the genes for a 2-oxo acid dehydrogenase (OADH) complex, but their presence remained a mystery because no enzymatic activity with any of the known OADH substrates could be found, and an inactivation of one of the genes did not lead to any phenotype. Here we report the identification of an additional oadh gene cluster in the genome of H. volcanii. In contrast to previously known oadh loci, it contains three genes, oadh2A1, oadh2A2, and oadh2ld, with coding capacity for the E1{alpha} and E1ß subunits and an unattached lipoyl domain, but it is devoid of the genes for a complete E2 and an E3. The genes were isolated by complementation of a nitrate respiration-deficient mutant of H. volcanii and therefore were shown to be functional in vivo. Phylogenetic analyses revealed that the deduced E1{alpha} and E1ß subunits of OADH2 group with bacterial acetoin dehydrogenases but not with the OADH1 subunits, and thus, H. volcanii has obtained the two gene groups independently. Comparison of the wild type and the mutant allowed us to exclude a function of OADH2 in the aerobic or anaerobic degradation of acetoin or glucose. Instead, it could be shown that OADH2 is important during nitrate-respirative growth on Casamino Acids. Many physiological and biochemical experiments failed to indicate that OADH2 uses any of the previously known OADH substrates. Growth potentials of the mutant were markedly different in media with a single carbon source versus media with mixed carbon sources.


* Corresponding author. Mailing address: Goethe-Universität, Biozentrum Niederursel, Marie-Curie-Str. 9, D-60439 Frankfurt, Germany. Phone and fax: 49-69-798 29564. E-mail: soppa{at}em.uni-frankfurt.de.


Journal of Bacteriology, June 2002, p. 3114-3121, Vol. 184, No. 11
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.11.3114-3121.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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