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Journal of Bacteriology, July 2009, p. 4286-4297, Vol. 191, No. 13
0021-9193/09/$08.00+0     doi:10.1128/JB.00145-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Autotrophic Carbon Dioxide Assimilation in Thermoproteales Revisited {triangledown}

W. Hugo Ramos-Vera, Ivan A. Berg, and Georg Fuchs*

Mikrobiologie, Fakultät Biologie, Albert Ludwigs Universität—Freiburg, Freiburg, Germany

Received 3 February 2009/ Accepted 24 April 2009

For Crenarchaea, two new autotrophic carbon fixation cycles were recently described. Sulfolobales use the 3-hydroxypropionate/4-hydroxybutyrate cycle, with acetyl-coenzyme A (CoA)/propionyl-CoA carboxylase as the carboxylating enzyme. Ignicoccus hospitalis (Desulfurococcales) uses the dicarboxylate/4-hydroxybutyrate cycle, with pyruvate synthase and phosphoenolpyruvate carboxylase being responsible for CO2 fixation. In the two cycles, acetyl-CoA and two inorganic carbons are transformed to succinyl-CoA by different routes, whereas the regeneration of acetyl-CoA from succinyl-CoA proceeds via the same route. Thermoproteales would be an exception to this unifying concept, since for Thermoproteus neutrophilus, the reductive citric acid cycle was proposed as a carbon fixation mechanism. Here, evidence is presented for the operation of the dicarboxylate/4-hydroxybutyrate cycle in this archaeon. All required enzyme activities were detected in large amounts. The key enzymes of the cycle were strongly upregulated under autotrophic growth conditions, indicating their involvement in autotrophic CO2 fixation. The corresponding genes were identified in the genome. 14C-labeled 4-hydroxybutyrate was incorporated into the central building blocks in accordance with the key position of this compound in the cycle. Moreover, the results of previous 13C-labeling studies, which could be reconciled with a reductive citric acid cycle only when some assumptions were made, were perfectly in line with the new proposal. We conclude that the dicarboxylate/4-hydroxybutyrate cycle is operating in CO2 fixation in the strict anaerobic Thermoproteales as well as in Desulfurococcales.

* Corresponding author. Mailing address: Mikrobiologie, Fakultät Biologie, Schänzlestr. 1, D-79104 Freiburg, Germany. Phone: 49-761-2032649. Fax: 49-761-2032626. E-mail: georg.fuchs{at}biologie.uni-freiburg.de

{triangledown} Published ahead of print on 1 May 2009.

Journal of Bacteriology, July 2009, p. 4286-4297, Vol. 191, No. 13
0021-9193/09/$08.00+0     doi:10.1128/JB.00145-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Kockelkorn, D., Fuchs, G. (2009). Malonic Semialdehyde Reductase, Succinic Semialdehyde Reductase, and Succinyl-Coenzyme A Reductase from Metallosphaera sedula: Enzymes of the Autotrophic 3-Hydroxypropionate/4-Hydroxybutyrate Cycle in Sulfolobales. J. Bacteriol. 191: 6352-6362 [Abstract] [Full Text]  


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