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Applied and Environmental Microbiology, January 1999, p. 339-341, Vol. 65, No. 1
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Symbiotic Deficiencies Associated with a coxWXYZ Mutant of Bradyrhizobium japonicum

Marci Ann Surpindagger and Robert J. Maier*

Department of Biology, The Johns Hopkins University, Baltimore, Maryland 21218-2685

Received 8 July 1998/Accepted 26 October 1998

The terminal oxidase complexes encoded by coxMNOP and coxWXYZ were studied by analysis of mutations in each of the two oxidases. Carbon monoxide difference spectra obtained from membranes of coxMNOP mutant bacteroids were like those obtained for the wild type, whereas bacteroid membranes of a coxWXYZ mutant were deficient in CO-reactive cytochrome b. Experiments involving cyanide inhibition of oxidase activity were consistent with the conclusion that the coxX mutant is deficient in a membrane-associated O2-binding component. The viable cell number (bacteria that could be recultured from crushed nodules) was 20 to 29% lower for the coxX mutant than for the wild-type or the CoxN- strain. In three separate greenhouse studies, nodules of a coxX mutant had significantly lower (28 to 34% less) acetylene reduction rates than the wild-type nodules did, and plants inoculated with a double mutant (coxMNOP coxWZYZ) had rates 30% lower than those of wild-type-inoculated plants.

* Corresponding author. Present address: Department of Microbiology, The University of Georgia, 527 Biological Sciences, Athens, GA 30602-2605. Phone: (706) 542-2323. Fax: (706) 542-2674. E-mail: rmaier{at}arches.uga.edu.

dagger Present address: Plant Biology Laboratory, The Salk Institute for Biological Studies, San Diego, CA 92186-5800.

Applied and Environmental Microbiology, January 1999, p. 339-341, Vol. 65, No. 1
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.




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