Oxygen defense systems in obligately thermophilic bacteria

Ten strains of Gram-negative, aerobic, obligately thermophilic bacteria were examined for their response to oxygen toxicity by comparing static with shaken cultures. All of the organisms tested had measurable levels of superoxide dismutase, catalase, and peroxidase. Aeration generally did not result in an increased level of superoxide dismutase in any of the thermophiles. Aeration of organisms obligate for n-alkane substrate caused an increase in cellular peroxidase levels and a corresponding decrease in catalase. The thermophiles that grew on either n-alkanes or complex media did not grow on the hydrocarbon in aerated culture but on a complex medium, aeration effected an increased level of catalase. With the exception of a pink-pigmented thermophile which, when aerated, did not have an increased level of the three oxygen defense enzymes, most of the thermophiles surveyed had an increased level of catalase or peroxidase when exposed to increased oxygen tension. The activity of the enzymes was determined at temperatures from 25 to 65 degrees C and the former temperature was satisfactory for these experiments.