A Study of Some Environmental Factors Which Control Endospore Formation by a Strain of Bacillus mycoides

Abstract

Accumulation of the byproducts of metabolism, such as the acid products of glycolysis, tends to inhibit sporulation. Oxygen may be necessary for some process in the formation of endospores, but its principal effect is in greatly increasing the rate of metabolism and the degree to which nutrients are utilized. As a result, there is a minimum accumulation of byproducts; e.g., glucose is oxidized to CO2 and probably water, and acids do not accumulate in the medium. Although endospores may be formed within a long interval of pH, there is an opt. between pH 6.6 and 6.8. The significance of this optimum is not clear, and may well be related to the utilization of nutrients and the accumulation of by-products. Vitamin B1 promotes sporulation (but does not seem to affect growth) on agar slants of a simple medium in which there is a tendency for acid by-products to accumulate; it has no effect on either growth or sporulation in agar slants of vitamin-free casein hydrolyzate in which no acid by-products accumulate. The effect of the vitamin in the synthetic medium is indirect and due to an increase in the rate of decarboxylation of the acid byproducts. It is assumed that the vitamin is readily synthesized in the casein hydrolyzate medium. Gradual drying does not usually affect sporulation unless it affects growth and the availability of nutrients. . With rare exceptions, when drying exerts an effect it is detrimental. Suspending vegetative cells in dist. water promotes sporulation of the uninjured cells. MgSO4 increases the vegetative population. It has a beneficial effect on sporulation when the O2 supply is low or limited. Endospores do not germinate in dist., water or in an incomplete medium, such as a synthetic medium without a source of available energy, but they readily germinate in the presence of the necessary nutrients, even if the environment is unsuitable for further growth. It is concluded that, in this strain of B. mycoides, endospores are formed most readily by healthy cells faced with starvation in the presence of O2.