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J Bacteriol. 1968 January; 95(1): 143-146
Copyright © 1968 American Society for Microbiology. All Rights Reserved.

Taxonomy of Azotomonas Species

Department of Bacteriology, University of Wisconsin, Madison, Wisconsin 53706

ABSTRACT

The ability of two strains of Azotomonas insolita and one strain classified only as Azotomonas species to use molecular nitrogen was investigated by use of several techniques. Molecular ¹⁵N₂ incorporation by growing cultures of Azotomonas was inconsistent and limited. In addition, attempts to demonstrate nitrogen fixation in growing cultures by the radioactive ¹³N₂ technique were negative. Experiments were done in which the total nitrogen content of a culture was determined by a micro-Kjeldahl method. None of these experiments resulted in a significant increase in total nitrogen. Attempts to show a diauxie effect, that is, transition from growth on NH₄⁺ to N₂, were also unsuccessful. Nitrogen fixation by cell-free extracts of A. insolita was negative, as determined by reduction of N₂ to NH₃, and reduction of cyanide, of acetylene, and of azide. These negative results suggest that the taxonomic reclassification of the genus Azotomonas should be considered.