This Article Full Text Full Text (PDF) Supplemental material Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Inoue, J.-I. Articles by Ohkuma, M. Search for Related Content PubMed PubMed Citation Articles by Inoue, J.-I. Articles by Ohkuma, M.

 Previous Article

Eukaryotic Cell, October 2007, p. 1925-1932, Vol. 6, No. 10
1535-9778/07/$08.00+0     doi:10.1128/EC.00251-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Hydrogen Production by Termite Gut Protists: Characterization of Iron Hydrogenases of Parabasalian Symbionts of the Termite Coptotermes formosanus ^,

Jun-Ichi Inoue,^1,2 Kanako Saita,^1, Toshiaki Kudo,¹ Sadaharu Ui,² and Moriya Ohkuma^1*

Environmental Molecular Biology Laboratory, RIKEN, Wako, Saitama 351-0198,¹ Division of Biotechnology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi 400-8510, Japan²

Received 12 July 2007/ Accepted 13 August 2007

Cellulolytic flagellated protists in the guts of termites produce molecular hydrogen (H₂) that is emitted by the termites; however, little is known about the physiology and biochemistry of H₂ production from cellulose in the gut symbiotic protists due to their formidable unculturability. In order to understand the molecular basis for H₂ production, we here identified two genes encoding proteins homologous to iron-only hydrogenases (Fe hydrogenases) in Pseudotrichonympha grassii, a large cellulolytic symbiont in the phylum Parabasalia, in the gut of the termite Coptotermes formosanus. The two Fe hydrogenases were phylogenetically distinct and had different N-terminal accessory domains. The long-form protein represented a phylogenetic lineage unique among eukaryotic Fe hydrogenases, whereas the short form was monophyletic with those of other parabasalids. Active recombinant enzyme forms of these two Fe hydrogenases were successfully obtained without the specific auxiliary maturases. Although they differed in their extent of specific activity and optimal pH, both enzymes preferentially catalyzed H₂ evolution rather than H₂ uptake. H₂ evolution, at least that associated with the short-form enzyme, was still active even under high hydrogen partial pressure. H₂ evolution activity was detected in the hydrogenosomal fraction of P. grassii cells; however, the vigorous H₂ uptake activity of the endosymbiotic bacteria compensated for the strong H₂ evolution activity of the host protists. The results suggest that termite gut symbionts are a rich reservoir of novel Fe hydrogenases whose properties are adapted to the gut environment and that the potential of H₂ production in termite guts has been largely underestimated.

---

* Corresponding author. Mailing address: Environmental Molecular Biology Laboratory, RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198, Japan. Phone: 81 48 467 9648. Fax: 81 48 462 4672. E-mail: mohkuma{at}riken.jp

Published ahead of print on 31 August 2007.

Supplemental material for this article may be found at http://ec.asm.org/.

Present address: Kumamoto Industrial Research Institute and Kumamoto University, Kumamoto 862-0901, Japan.

---

Eukaryotic Cell, October 2007, p. 1925-1932, Vol. 6, No. 10
1535-9778/07/$08.00+0     doi:10.1128/EC.00251-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Hongoh, Y., Sharma, V. K., Prakash, T., Noda, S., Toh, H., Taylor, T. D., Kudo, T., Sakaki, Y., Toyoda, A., Hattori, M., Ohkuma, M. (2008). Genome of an Endosymbiont Coupling N2 Fixation to Cellulolysis Within Protist Cells in Termite Gut. Science 322: 1108-1109 [Abstract] [Full Text]