Thermal penicillinase derepression and temperature dependence of penicillinase production inducible and constitutive strains of Bacillus cereus

The basal level of penicillinase production in strain 569 reaches a maximum at 42 °. The induction ratio (induced/basal) reaches a maximum (42.6) at approximately 30 ° and falls to approximately 1.4 at 42 °. Culturing Bacillus cereus 569 (inducible) at 42 ° and lowering the temperature leads to an increase in penicillinase production (thermal derepression) equal to the level induced by cephalothin (CT). As reported earlier, induction in strain 569 at 42 ° does not occur when the cells are treated with a penicillin, here the analogue CT, at 42 °; however, treatment with CT at 37 ° followed by incubation at 42 ° gave the induced response. Constitutive mutants 569/H and 5/B showed a twofold change in the level of penicillinase upon going from 20 ° to 46 °, with specific activity increasing steadily to 46 °. A model is presented to explain these and other related data in the B. cereus penicillinase system.