Failure of Putative Nitrogen-fixing Bacteria to Fix Nitrogen

SUMMARY Analyses, tests with isotopic nitrogen and tests for acetylene and isocyanide reduction, using both continuous and batch cultures, were made with seven strains of putative nitrogen-fixing bacteria and three local isolates. Only two (single strains of Mycobacterium flavum and Pseudomonas azotogensis) fixed nitrogen; the active pseudomonad differed in several respects from the organism originally reported. Other Pseudomonas, Nocardia and Azotomonas species and the three local isolates did not fix; some simulated nitrogen fixation in cultural tests most impressively, but proved simply to be very efficient scavengers of traces of fixed nitrogen.