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Journal of Bacteriology, October 2006, p. 6808-6815, Vol. 188, No. 19
0021-9193/06/$08.00+0     doi:10.1128/JB.00781-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Biochemical and Molecular Characterization of the Biosynthesis of Glutamine and Glutamate, Two Major Compatible Solutes in the Moderately Halophilic Bacterium Halobacillus halophilus{dagger}

Stephan H. Saum,1,{ddagger} Jasmin F. Sydow,2,{ddagger},§ Peter Palm,3 Friedhelm Pfeiffer,3 Dieter Oesterhelt,3 and Volker Müller1,2*

Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, Frankfurt am Main, Germany,1 Microbiology, Department of Biology I, Ludwig Maximilians University, Munich, Germany,2 Max-Planck-Institute of Biochemistry, Department of Membrane Biochemistry, Martinsried, Germany3

Received 31 May 2006/ Accepted 13 July 2006

The moderately halophilic, chloride-dependent bacterium Halobacillus halophilus produces glutamate and glutamine as main compatible solutes at external salinities of 1.0 to 1.5 M NaCl. The routes for the biosynthesis of these solutes and their regulation were examined. The genome contains two genes potentially encoding glutamate dehydrogenases and two genes for the small subunit of a glutamate synthase, but only one gene for the large subunit. However, the expression of these genes was not salt dependent, nor were the corresponding enzymatic activities detectable in cell extracts of cells grown at different salinities. In contrast, glutamine synthetase activity was readily detectable in H. halophilus. Induction of glutamine synthetase activity was strictly salt dependent and reached a maximum at 3.0 M NaCl; chloride stimulated the production of active enzyme by about 300%. Two potential genes encoding a glutamine synthetase, glnA1 and glnA2, were identified. The expression of glnA2 but not of glnA1 was increased up to fourfold in cells adapted to high salt, indicating that GlnA2 is the glutamine synthetase involved in the synthesis of the solutes glutamate and glutamine. Furthermore, expression of glnA2 was stimulated twofold by the presence of chloride ions. Chloride exerted an even more pronounced effect on the enzymatic activity of preformed enzyme: in the absence of chloride in the assay buffer, glutamine synthetase activity was decreased by as much as 90%. These data demonstrate for the first time a regulatory role of a component of common salt, chloride, in the biosynthesis of compatible solutes.

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

§ Present address: Institut de Biologia Molecular de Barcelona (CSIC) and Institut de Recerca Biomedica, Parc Cientific de Barcelona, Barcelona, Spain.

{ddagger} S.H.S. and J.F.S. contributed equally to this study.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, October 2006, p. 6808-6815, Vol. 188, No. 19
0021-9193/06/$08.00+0     doi:10.1128/JB.00781-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Saum, S. H., Muller, V. (2007). Salinity-Dependent Switching of Osmolyte Strategies in a Moderately Halophilic Bacterium: Glutamate Induces Proline Biosynthesis in Halobacillus halophilus. J. Bacteriol. 189: 6968-6975 [Abstract] [Full Text]  


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