Carbon Monoxide Inhibition of Azotobacter in Microrespiration Experiments.

Extremely small quantities of carbon monoxide in air inhibit nitrogen fixation by red clover plants inoculated with Rhizobium trifolii (Lind and Wilson, 1941). In preliminary trials with Azotobacter vinelandii Wyss (1941) found a similar inhibition at carbon monoxide concentrations about 10 times those required for the symbiotic system. We have made a detailed study of the inhibition of this azotobacter using several sources of combined nitrogen to determine specificity for the nitrogen fixation process. Two methods have been used, each of which possesses certain advantages: a macro method which periodically measures directly the nitrogen fixed and a micro method which indirectly estimates nitrogen fixation by determining the increase in rate of respiration with time. The macro method is relatively longtime, 30-40 hr in comparison with the 4-7 hr required in the respiration studies. The results of the macro experiments have been described by Lind and Wilson (1942); in this paper the micro-respiration data are discussed.