Carbon Monoxide Inhibition of Azotobacter in Microrespiration Experiments

Abstract

Nitrogen fixation by Azotobacter vinelandii is specifically inhibited by carbon monoxide in micro-respiration experiments. The range in which specific inhibition obtains (0.1-0.5%) is about 10 times greater than is required for a similar inhibition of the symbiotic system in inoculated red clover plants. The results of these experiments are almost identical with those obtained in macro total nitrogen studies and thus confirm the reliability of the indirect micro-respiration method for investigating the mechanism of biological nitrogen fixation. Azotobacter kept on N-free medium in air assimilates ammonium and urea somewhat more rapidly than N/sub 2/. The rate of uptake of nitrate, nitrite and asparagine is low and variable. The same is true even to a greater degree with aspartate and glutamate. When cultures are adapted to these sources of nitrogen, i.e., previously grown in their presence, the rate of assimilation of nitrate and nitrite equals or even slightly exceeds N/sub 2/ fixation. Uptake of asparagine is likewise improved. The results of adaptation with aspartate and glutamate were inconclusive. 9 references, 6 figures, 5 tables.