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Journal of Bacteriology, November 1998, p. 5689-5696, Vol. 180, No. 21
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

A Cytochrome cbb3 (Cytochrome c) Terminal Oxidase in Azospirillum brasilense Sp7 Supports Microaerobic Growth

Kathleen Marchal,1 Jun Sun,1 Veerle Keijers,1 Huub Haaker,2 and Jos Vanderleyden1,*

F.A. Janssens Laboratory of Genetics, KULeuven, 3001 Heverlee, Belgium,1 and Department of Biochemistry, Agricultural University, 6703 HA Wageningen, The Netherlands2

Received 25 March 1998/Accepted 17 August 1998

Spectral analysis indicated the presence of a cytochrome cbb3 oxidase under microaerobic conditions in Azospirillum brasilense Sp7 cells. The corresponding genes (cytNOQP) were isolated by using PCR. These genes are organized in an operon, preceded by a putative anaerobox. The phenotype of an A. brasilense cytN mutant was analyzed. Under aerobic conditions, the specific growth rate during exponential phase (µe) of the A. brasilense cytN mutant was comparable to the wild-type specific growth rate (µe of approximately 0.2 h-1). In microaerobic NH4+-supplemented conditions, the low respiration of the A. brasilense cytN mutant affected its specific growth rate (µe of approximately 0.02 h-1) compared to the wild-type specific growth rate (µe of approximately 0.2 h-1). Under nitrogen-fixing conditions, both the growth rates and respiration of the wild type were significantly diminished in comparison to those under NH4+-supplemented conditions. Differences in growth rates and respiration between the wild type and the A. brasilense cytN mutant were less pronounced under these nitrogen-fixing conditions (µe of approximately 0.03 h-1 for the wild type and 0.02 h-1 for the A. brasilense cytN mutant). The nitrogen-fixing capacity of the A. brasilense cytN mutant was still approximately 80% of that determined for the wild-type strain. This leads to the conclusion that the A. brasilense cytochrome cbb3 oxidase is required under microaerobic conditions, when a high respiration rate is needed, but that under nitrogen-fixing conditions the respiration rate does not seem to be a growth-limiting factor.

* Corresponding author. Mailing address: F.A. Janssens Laboratory of Genetics, KULeuven, Kardinaal Mercierlaan 92, 3001 Heverlee, The Netherlands. Phone: 32 16 329679. Fax: 32 16 321966. E-mail: jozef.vanderleyden{at}agr.kuleuven.ac.be.

Journal of Bacteriology, November 1998, p. 5689-5696, Vol. 180, No. 21
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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