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Spore Refractility in Variants of Bacillus cereus Treated with Actinomycin D

^a Department of Bacteriology and Immunology, University of Western Ontario, London 72, Ontario
Department of Biochemistry, University of Western Ontario, London 72, Ontario

ABSTRACT

Refractility as indicated by light microscopy, electron microscopy of thin sections, and freeze fracture etching was increased and maintained in a cortexless mutant, A(–)1, of Bacillus cereus var. alesti by the addition during sporulation stage 4 of actinomycin D, which prevents the terminal lysis of spore core associated with sporulation in this organism. ⁴⁵Calcium uptake levels and dipicolinic acid (DPA) content were similarly maintained. The location of these components appears to be in the spore protoplast. In the parent A(–), treated with actinomycin D during stage 4, spore particles with similar morphology to the mutant, that is without a cortex and with the characteristics of refractility, were obtained. A major difference in sensitivity to actinomycin D between the processes of ⁴⁵Ca uptake and DPA synthesis was observed. Some heat resistance in A(–) made cortexless by actinomycin D could be observed. These studies indicate that the role of the cortex is not to produce the dehydrated refractile spore state but to maintain it.

¹ M.R.C. Research Associate, Medical Research Council of Canada.

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