The viability of spores of some Bacillus species

The percentage of spores of Bacillus subtilis capable of giving rise to macro-colonies (“viability”) has been determined. Under optimum conditions (heat-activation and inclusion of dextrose in the counting medium) about 30% of spores formed colonies. This figure appeared to increase to about 70% on prolonged cold storage (0–10°). The viability of spores decreased with increase in the manganese content of the sporulation medium. Spores of four other species of Bacillus examined were not heat-activatable and were unaffected by the dextrose content of the counting medium. They showed viabilities of 40–75%.