Freeze-dried Bacillus megaterium IAM 1166 spores humidified with water vapor to a water content of above 30% germinated spontaneously without the addition of any germinant. Differential scanning calorimetric thermogram of the spores thus germinated had absorption peaks at about 100° and 130° other than a large peak due to the evaporation of spore water. Both 100° and 130° peaks were characteristic of spores germinating spontaneously by water vapor and corresponded to those in the standard Ca-DPA precipitate deposited at room temperature. The reflection spectra of germinated spores also agreed with those of the standard Ca-DPA. Since the weight decrease in thermogravi-metric analysis, the water content by the Karl Fischer method, and the elementary analysis of the standard Ca-DPA showed that 1mol of Ca-DPA was bound by 1.5mol of H2O, it was concluded that 1mol of Ca-DPA in germinated spores was hydrated by 1.5mol of H2O. It is also suggested that the macromolecule-Ca-DPA complex in dormant spores might be transformed into a free state of Ca-DPA hydrate by water vapor, produces more Ca-DPA hydrate molecules autocatalytically, and thus triggers the spontaneous germination by setting free more and more functional macromolecules.
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Maeda et al. (1974) studied this question.