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J Bacteriol. 1969 March; 97(3): 1093-1098
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Nitrogen Fixation by Rhodospirillum rubrum Grown in Nitrogen-limited Continuous Culture¹

^a Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706

ABSTRACT

Cell-free extracts of the photosynthetic bacterium Rhodospirillum rubrum were inconsistent in reducing N₂. An internally illuminated fermentor, designed for the continuous culture of this organism on N₂ under nitrogen-limited conditions, produced cells which yielded cell extracts with consistent activity for cell-free N₂ fixation. A nitrogen-limited continuous culture, supplied ammonia rather than N₂, gave cell-free extracts with even more active N₂ fixation. Extracts of cells grown in the fermentor with glutamate nitrogen as the limiting nutrient in continuous culture did not reduce N₂, but whole cells fixed ¹⁵N-enriched N₂. The discovery that cells from ammonia and glutamate nitrogen-limited continuous cultures are capable of N₂ reduction suggests that R. rubrum cells produce the N₂-reducing enzymes in response to conditions of nitrogen deficiency rather than in response to the presence of N₂. Examination of the effect of the pN₂ on N₂ reduction by cell-free preparations of R. rubrum indicated that the K(N₂) is approximately 0.071 atm. Cell-free extracts from R. rubrum were tested for their ability to reduce substrates other than N₂.

² Present address: Enchanter, Inc., Oceanographic Research, Costa Mesa, Calif. 92627.

¹ Published with the approval of the Director of the Wisconsin Agricultural Experiment Station.

This article has been cited by other articles:

• Ludden, P., Burris, R. (1976). Activating factor for the iron protein of nitrogenase from Rhodospirillum rubrum. Science 194: 424-426 [Abstract]