Oxygen and "strictly anaerobic" intestinal bacteria. II. Oxygen metabolism in strictly anaerobic bacteria.

Oxygen metabolism of "strictly anaerobic" intestinal bacteria was investigated and compared in 25 strains. Washed cell suspensions of all the bacterial strains, in which growth in a medium initially equilibrated with a gas mixture consisting of 5% O2, 5% CO2, and 90% N2 was almost the same as under anaerobic conditions, absorbed O2 at high rate. Such O2 uptake was inhibited by NaN3. Most strains in which growth was inhibited either partially or completely in the same oxygenic condition absorbed O2 at a comparably low rate, and in many cases, such O2 uptake was not inhibited by NaN3. However, in a certain strain incapable of growth in the initial presence of dissolved O2, absorption of O2 was as high as that in some aerobic bacteria, and it was inhibited by NaN3. Little interrelationship was found between the degree of oxygen tolerance and the activities of NADH-peroxidase, H2O2-splitting reaction or superoxide dismutase. A slight interrelationship seems to be present in the case of NADH oxidase even though many exceptions were recognized. All the strains studied had the activities of superoxide dismutase, the absence of which has been regarded as the enzymatic basis of strict anaerobiosis of "strictly anaerobic" bacteria. Some strict anaerobes had high an activity of this enzyme as some aerobic bacteria. The differences in the levels of this activity seem to have some interrelationship not with differences in the degree of oxygen tolerance but with those in the genus to which every strain belongs taxonomically.