Taxonomy of Azotomonas species.

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 (15)N(2) incorporation by growing cultures of Azotomonas was inconsistent and limited. In addition, attempts to demonstrate nitrogen fixation in growing cultures by the radioactive (13)N(2) 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 NH(4) (+) to N(2), were also unsuccessful. Nitrogen fixation by cell-free extracts of A. insolita was negative, as determined by reduction of N(2) to NH(3), and reduction of cyanide, of acetylene, and of azide. These negative results suggest that the taxonomic reclassification of the genus Azotomonas should be considered.