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Applied and Environmental Microbiology, March 2007, p. 1665-1671, Vol. 73, No. 5
0099-2240/07/$08.00+0     doi:10.1128/AEM.02565-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Redirection of Metabolism for Biological Hydrogen Production{triangledown} ,{dagger}

Federico E. Rey,1,2 Erin K. Heiniger,1 and Caroline S. Harwood1*

Department of Microbiology, University of Washington, Seattle, Washington 98195-7242,1 Department of Microbiology, University of Iowa, Iowa City, Iowa 522422

Received 2 November 2006/ Accepted 3 January 2007

A major route for hydrogen production by purple photosynthetic bacteria is biological nitrogen fixation. Nitrogenases reduce atmospheric nitrogen to ammonia with the concomitant obligate production of molecular hydrogen. However, hydrogen production in the context of nitrogen fixation is a rather inefficient process because about 75% of the reductant consumed by the nitrogenase is used to generate ammonia. In this study we describe a selection strategy to isolate strains of purple photosynthetic bacteria in which hydrogen production is necessary for growth and independent of nitrogen fixation. We obtained four mutant strains of the photosynthetic bacterium Rhodopseudomonas palustris that produce hydrogen constitutively, even in the presence of ammonium, a condition where wild-type cells do not accumulate detectable amounts of hydrogen. Some of these strains produced up to five times more hydrogen than did wild-type cells growing under nitrogen-fixing conditions. Transcriptome analyses of the hydrogen-producing mutant strains revealed that in addition to the nitrogenase genes, 18 other genes are potentially required to produce hydrogen. The mutations that caused constitutive hydrogen production mapped to four different sites in the NifA transcriptional regulator in the four different strains. The strategy presented here can be applied to the large number of diverse species of anoxygenic photosynthetic bacteria that are known to exist in nature to identify strains for which there are fitness incentives to produce hydrogen.

* Corresponding author. Mailing address: Department of Microbiology, Box 357242, 1959 N. E. Pacific Street, University of Washington, Seattle, WA 98195-7242. Phone: (206) 221-2848. Fax: (206) 543-8297. E-mail: csh5{at}u.washington.edu.

{triangledown} Published ahead of print on 12 January 2007.

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

Applied and Environmental Microbiology, March 2007, p. 1665-1671, Vol. 73, No. 5
0099-2240/07/$08.00+0     doi:10.1128/AEM.02565-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Zou, X., Zhu, Y., Pohlmann, E. L., Li, J., Zhang, Y., Roberts, G. P. (2008). Identification and functional characterization of NifA variants that are independent of GlnB activation in the photosynthetic bacterium Rhodospirillum rubrum. Microbiology 154: 2689-2699 [Abstract] [Full Text]  


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