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Bacillus stearothermophilus was adapted to 37 ~ C (mesophilic culture) and to 55~ (thermophilic culture) by cultivation via an intermediate temperature of 46~ In the crude extract of the thermophilic bacterial cells the glucokinase, glucose-6-phoslahate dchydrogenase, glyeeraldehyde-3-phosphate dehydrogenase and isocitrate dehydrogenase are more thermostable than the corresponding enzymes in the crude extract of mesophilic cells. At the intermediate temperature of 46~ both types are probably formed.
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37 ~ C-precultures of Bacillus caldotenax were further cultivated (in different samples) at 5~ intervals between 30~ and 70~ It was shown that in 70~ of the above mentioned enzymes more thermostable forms and in 37 ~ C-cells more thermolabile forms are present.
Furthermore, as demonstrated in the case of glucose-6-phosPhatc isomerase and isocitrate dehydrogenase, cells cultured in the temperature range between 30--50~ produced thermolabile enzyme variants (M-type), while cultures between 60--70~ produced thermostable variants (Th-type). At cultivation temperatures above 50~ a pronounced lag-period expressing the metabolic changes was found. In the lagperiod, mesophilic enzymes are no longer present as early as 20 min after increasing the temperature (70~ and synthesis of thermostable enzymes starts about 1 h before the beginning of growth.
- Similar results were obtained with Bacillus caldotenax precultivated at 70~ and cultivated between 30~ and 70 ~ C.