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Journal of Bacteriology, July 2000, p. 3854-3857, Vol. 182, No. 13
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Role of the Azotobacter vinelandii Nitrogenase-Protective Shethna Protein in Preventing Oxygen-Mediated Cell Death

R. J. Maier* and F. Moshiridagger

Department of Microbiology, University of Georgia, Athens, Georgia 30602-2605

Received 21 January 2000/Accepted 7 April 2000

Azotobacter vinelandii strains lacking the nitrogenase-protective Shethna protein lost viability upon carbon-substrate deprivation in the presence of oxygen. This viability loss was dependent upon the N2-fixing status of cultures (N2-fixing cells lost viability, while non-N2-fixing cells did not) and on the ambient O2 level. Supra-atmosheric O2 tensions (40% partial pressure) decreased the viable cell number of the mutant further, and the mutant had a slightly higher spontaneous mutation frequency than the wild type in the high-O2 conditions. Iron starvation conditions, which resulted in fourfold-reduced superoxide dismutase levels, were also highly detrimental to the viability of the protective protein mutants, but these conditions did not affect the viability of the wild-type strain. Nitrogenase or other powerful reductants associated with N2 fixation may be sources of damaging partially reduced oxygen species, and the production of such species are perhaps minimized by the Shethna protein.

* Corresponding author. Mailing address: University of Georgia, Department of Microbiology, 815 Biological Sciences Bldg., Athens, GA 30602-2605. Phone: (706) 542-2323. Fax: (706) 542-2674. E-mail: rmaier{at}arches.uga.edu.

dagger Present address: The Monsanto Company, St. Louis, MO 63198.

Journal of Bacteriology, July 2000, p. 3854-3857, Vol. 182, No. 13
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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