Apart from their utility in regulation of pH, bicarbonates may promote the formation of spores by increasing COo concentration, as shown by Powell and Hunter (1955). Proliferating vegetative cells, when centrifuged, washed, and shaken in distilled water, form spores only if the prior growth medium is conducive to sporulation. However, B. subtilis derived from an asporogenous medium sporulates in distilled water when supplied with both yeast extract and salts, but not if one of these supplements is omitted (Murrell, 1955), indicating that the spore-generating mechanism is not seriously impaired by limited cultivation in asporogenous media. The known facts, briefly surveyed, indicate that mineral salts are essential for the formation of bacterial spores. The fact that synthetic media without added salts do not produce spores, and the fact that the inadequacy for spore formation of many complex organic media can be corrected by the addition of suitable minerals support this contention. The level of minerals required for sporulation varies with the organism and with cultural conditions such as kind and concentration of nutrients, oxygen supply, temperature, and pH. The importance of manganese in the sporulating process is conspicuously evident. It is required by a wide variety of mesophilic and thermophilic aerobes, at concentrations above those needed for active vegetative growth, and, with one apparent exception, cannot be replaced by any other mineral element. Manganese has been found to broaden the temperature and pH range over which sporulation occurs (Amaha et al, 1956).
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