This Article Full Text Full Text (PDF) Other Versions of this Article: AEM.01160-07v1 73/23/7562    most recent 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 Google Scholar Google Scholar Articles by Masukawa, H. Articles by Sakurai, H. Search for Related Content PubMed PubMed Citation Articles by Masukawa, H. Articles by Sakurai, H. Agricola Articles by Masukawa, H. Articles by Sakurai, H.

 Previous Article  |  Next Article 

Applied and Environmental Microbiology, December 2007, p. 7562-7570, Vol. 73, No. 23
0099-2240/07/$08.00+0     doi:10.1128/AEM.01160-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Effects of Disruption of Homocitrate Synthase Genes on Nostoc sp. Strain PCC 7120 Photobiological Hydrogen Production and Nitrogenase

Department of Biological Sciences, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293,¹ Department of Biology, School of Education, Waseda University, Nishiwaseda 1, Shinjuku, Tokyo 169-8050, Japan²

Received 23 May 2007/ Accepted 30 September 2007

In the case of nitrogenase-based photobiological hydrogen production systems of cyanobacteria, the inactivation of uptake hydrogenase (Hup) leads to significant increases in hydrogen production activity. However, the high-level-activity stage of the Hup mutants lasts only a few tens of hours under air, a circumstance which seems to be caused by sufficient amounts of combined nitrogen supplied by active nitrogenase. The catalytic FeMo cofactor of nitrogenase binds homocitrate, which is required for efficient nitrogen fixation. It was reported previously that the nitrogenase from the homocitrate synthase gene (nifV) disruption mutant of Klebsiella pneumoniae shows decreased nitrogen fixation activity and increased hydrogen production activity under N₂. The cyanobacterium Nostoc sp. strain PCC 7120 has two homocitrate synthase genes, nifV1 and nifV2, and with the hupL variant of Nostoc sp. strain PCC 7120 as the parental strain, we have constructed two single mutants, the hupL nifV1 strain (with the hupL and nifV1 genes disrupted) and the hupL nifV2 strain, and a double mutant, the hupL nifV1 nifV2 strain. Diazotrophic growth rates of the two nifV single mutants and the double mutant were decreased moderately and severely, respectively, compared with the rates of the parent hupL strain. The hydrogen production activity of the hupL nifV1 mutant was sustained at higher levels than the activity of the parent hupL strain after about 2 days of combined-nitrogen step down, and the activity in the culture of the former became higher than that in the culture of the latter. The presence of N₂ gas inhibited hydrogen production in the hupL nifV1 nifV2 mutant less strongly than in the parent hupL strain and the hupL nifV1 and hupL nifV2 mutants. The alteration of homocitrate synthase activity can be a useful strategy for improving sustained photobiological hydrogen production in cyanobacteria.

Published ahead of print on 12 October 2007.