Relationship between cortex content and properties of Bacillus sphaericus spores

Abstract

The muramic lactam content of spores of B. sphaericus mutants defective in meso diaminopimelic acid synthesis increased almost linearly with an increase of meso diaminopimelic acid concentration in the medium. Since muramic lactam content is a measure of cortex content, the amount of cortex in spores of the mutants can be easily varied by changing the meso diaminopimelic acid concentration in the medium. Characteristic properties were tested in spores containing different amounts of cortex. Critical amounts of cortex were associated with different spore properties. Refractility and dipicolinic acid accumulation in the spores both required about 20% of the maximum cortex content (although refractility is independent of dipicolinic acid content). For xylene and octanol resistance, about 25% of the maximum cortex content was required. However, for heat resistance, more than 90% of the maximum cortex content was required; heat resistance was, therefore, more closely related to the amount of cortex than to the amount of dipicolinic acid in the spore. Furthermore, for accumulation of Ca2+ in the spore, the existence of both cortex and dipicolinic acid in the spore was essential.