Abstract
Conclusions and Summary
(1) Temperature and atmosphere exert an important influence upon the effects produced by ultraviolet irradiation of the mesophile and thermophile studied. These effects are noted even in the relatively inert spore stage of each. Although the thermophile was more sensitive than the mesophile to the lethal action of a given dose of ultraviolet radiation, it was affected to a lesser degree by changes in temperature during irradiation in the air. Temperature changes exerted almost no effect upon the thermophile when oxygen was excluded from the suspension during irradiation, while the mesophile was markedly affected. This would be the expected result if the thermophile possessed heat-stable nuclear proteins, and damage due to the radiation were not additive with that resulting from heat-denaturation. Mutation incidence at 99.9% killing fell to below normal levels at 75 and 100°C for the mesophile and thermophile, respectively, possibly due to selection. (2) The relative mutability of the two was also confirmed by the determination of fermentation (mannose) mutants, and by isolation of biochemical mutants using the Davis(12) technic. Such mutants were readily isolated from B. globigii cultures, but only a limited number of vitaminless and amino acidless, and no purineless or pyrimidineless mutants could be isolated from the thermophilic cultures. Generally, the thermophile was much less mutabile than the mesophile as compared by streptomycin resistant, fermentation and biochemical mutants.
Get full access to this article
View all access options for this article.