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Journal of Bacteriology, April 2007, p. 2805-2812, Vol. 189, No. 7
0021-9193/07/$08.00+0     doi:10.1128/JB.01360-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

A Novel Ferredoxin-Dependent Glutamate Synthase from the Hydrogen-Oxidizing Chemoautotrophic Bacterium Hydrogenobacter thermophilus TK-6{triangledown}

Masafumi Kameya, Takeshi Ikeda, Miyuki Nakamura, Hiroyuki Arai, Masaharu Ishii,* and Yasuo Igarashi

Department of Biotechnology, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan

Received 28 August 2006/ Accepted 9 January 2007

Glutamate synthases are classified according to their specificities for electron donors. Ferredoxin-dependent glutamate synthases had been found only in plants and cyanobacteria, whereas many bacteria have NADPH-dependent glutamate synthases. In this study, Hydrogenobacter thermophilus, a hydrogen-oxidizing chemoautotrophic bacterium, was shown to possess a ferredoxin-dependent glutamate synthase like those of phototrophs. This is the first observation, to our knowledge, of a ferredoxin-dependent glutamate synthase in a nonphotosynthetic organism. The purified enzyme from H. thermophilus was shown to be a monomer of a 168-kDa polypeptide homologous to ferredoxin-dependent glutamate synthases from phototrophs. In contrast to known ferredoxin-dependent glutamate synthases, the H. thermophilus glutamate synthase exhibited glutaminase activity. Furthermore, this glutamate synthase did not react with a plant-type ferredoxin (Fd3 from this bacterium) containing a [2Fe-2S] cluster but did react with bacterial ferredoxins (Fd1 and Fd2 from this bacterium) containing [4Fe-4S] clusters. Interestingly, the H. thermophilus glutamate synthase was activated by some of the organic acids in the reductive tricarboxylic acid cycle, the central carbon metabolic pathway of this organism. This type of activation has not been reported for any other glutamate synthases, and this property may enable the control of nitrogen assimilation by carbon metabolism.

* Corresponding author. Mailing address: Department of Biotechnology, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan. Phone: (81)-3-5841-5143. Fax: (81)-3-5841-5272. E-mail: amishii{at}mail.ecc.u-tokyo.ac.jp.

{triangledown} Published ahead of print on 19 January 2007.

Journal of Bacteriology, April 2007, p. 2805-2812, Vol. 189, No. 7
0021-9193/07/$08.00+0     doi:10.1128/JB.01360-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Miura, A., Kameya, M., Arai, H., Ishii, M., Igarashi, Y. (2008). A Soluble NADH-Dependent Fumarate Reductase in the Reductive Tricarboxylic Acid Cycle of Hydrogenobacter thermophilus TK-6. J. Bacteriol. 190: 7170-7177 [Abstract] [Full Text]  


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