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SUMMARY Many different strains of Bacillus cereus and members of other species of the genus Bacillus were induced to lyse by exposure to the proper concentration of mitomycin C, a radiomimetic drug. For some bacilli, induction of lysis occurred only in Casamino acids containing medium but not in nutrient broth +yeast extract medium, whereas other bacilli showed the opposite behaviour. The efficiency of induction was a function of the growth phase of the culture and of the concentration of mito- mycin C. Induction of lysis in B. thuringiensis resulted in the release of oedema factor and phospholipase into the medium. Mitomycin C-induced lysis of B. cereus was prevented by adding chloramphenicol, actino- mycin D, or 5-fluorouracil deoxyriboside up to 40 min. later. There appeared to be no sequential loss of susceptibility to inhibition by these compounds as expected. INTRODUCTION The close relationship between lysis induced by ultraviolet ( u.v.) radiation and the production of the oedema-producing toxin by a strain of Bacillus cereus (6464) was reported by Altenbern (1962). Further work showed that either u.v.-radiation or mitomycin C, a radiomimetic agent, could be used as an inducing agent. Many other strains of B. cereus tested gave mitomycin C-induced lysis like that ob- served for strain 6464. The study was then expanded to include many species of the genus Bacillus and sometimes several strains of a species. The present paper is mainly a survey of the action of mitomycin C on members of the genus Bacillus, including the effect of medium on ease of induction, the rate of induced lysis, the production of phospholipase and toxin by strains of B. thuringiensis and B. anthracis, and the effects of chloramphenicol, actinomycin D and 5-fluorouracil deoxyriboside on the course of mitomycin C-induced lysis in certain species. METHODS The various organisms used in this work were maintained as spore stocks in soil. Regular spore suspensions were prepared from potato-extract agar slopes as described by Thorne (1962). Two media were routinely used: (1) the Casamino acids medium; (2) the nutrient broth +yeast extract-medium (NBY) described by Thorne (1962). Cultures of the various organisms in logarithmic growth were prepared by in- oculation of tubes with 5 ml. of either of the liquid media with enough spores to give finally 106 sporeslml. These tubes were then incubated on a shaker at 37" until the

Inducible Lytic Systems in the Genus Bacillus