The effect of sporulation temperature on sporal characteristics ofBacillus subtilis A
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Spores ofBacillus subtilis A were produced at different temperatures (23°–49°C) and examined for a number of sporal characteristics. Spore heat resistance increased with sporulation temperature to 45°C, with spores grown at 49°C showing a dramatic reduction in resistance. Spore crops showed biphasic thermal death curves whether enumerated on germination medium with or without calcium dipicolinate. This strain produces both rough and smooth variants. Of the spores produced at 23°C, 99% were rough, had a density of 1.305, and an average core/core + cortex volume ratio of 0.1838. At 49°C, 99% were smooth, had a density of 1.275, and an average volume ratio of 0.3098. Between these temperatures both spore types were produced. There appeared to be no direct correlation with sporulation temperature, heat resistance, and dipicolinate content. There was an increase in both the magnesium and calcium contents to 45°C with a dramatic reduction at 49°C. The 1.305 density spores had higher calcium and dipicolinate contents than the 1.275 spores, although both spore types showed biphasic thermal death curves. The mechanisms involved in determining which spore type (rough/smooth) is produced at a specific growth temperature is unknown.
KeywordsVolume Ratio Growth Temperature Specific Growth Average Volume Heat Resistance
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