The differential effect of actinomycin D on the biosynthesis of enzymes in Bacillus subtilis and Bacillus cereus

Abstract

Relatively low concentrations (0.05–0.1 μg/ml) of actinomycin D cause marked inhibition of the growth of Bacillus cereus and Bacillus subtilis and have a striking differential effect on enzyme production. In B. subtilis a concentration of the drug causing 30% inhibition of growth will almost abolish induction of α-glucosidase (α- d-glucoside glucohydrolase, EC 3.2.1.20) without affecting penicillinase (penicillin amidohydrolase, EC 3.5.2.6) induction. In B. cereus the sensitivity of the penicillinase-forming system to inhibition by actinomycin depends upon the state of inducibility and the stage of induction: in preinduced cultures of the inducible strain, the system is temporarily (up to 40 min) much more resistant than in cells induced simultaneously with addition of the drug; whereas in the constitutive mutant it is unaffected for nearly 2 h. Very low concentrations of actinomycin (0.01–0.025 μg/ml) may stimulate the rate of induced penicillinase formation in B. subtilis by up to 100%, but have much less effect, if any, on production of the enzyme in constitutive mutants. These findings are believed to lend some support to the messenger RNA hypothesis as applied to enzyme formation in these organisms and suggest that messenger RNA for penicillinase formation in B. cereus may be metabolically stable for up to 40 min. They also suggest the possibility that the differential effect of actinomycin (at concentrations insufficient to saturate the DNA of the cell) may be due to differences in its combining affinity for different genes.