Dormancy of Bacterial Endospores: Regulation of Electron Transport by Dipicolinic Acid.

One of the most common features in the metamorphism of diverse biological systems is the conversion of these systems into a quiescent, dormant state. Although the properties of these dormant states have in general been well described (inert or weak metabolic activity and resistance to external chemical and physical factors), there is relatively little information on the internal regulatory mechanisms involved in either maintaining the dormant state or elevating its conversion to a metabolically active form. In microbes these stages are well illustrated by the processes of sporulation and germination of bacterial endospores. The mature endospore is a highly refractile body which is resistant to heat and chemical agents and, although it contains several enzymes, is inert metabolically. Activation evokes a latent carbohydrate metabolizing system, a number of individual enzymes, and prepares the system for a triggered germination with loss of heat resistance upon the addition of simple germinating agents. ' These observations, together with the dependence of over-all germination on metabolic activity,2 suggest an enzymic regulatory mechanism for dormancy. A priori one would expect this regulatory mechanism to reflect some fundamental chemical or biochemical difference between the dormant and vegetative states. Two such dramatic differences are the unique presence in spores of DPA', I and elevated levels of divalent metals.4' 5 Our attention was directed toward these components as playing a role in dormancy, since (i) DPA synthesis and divalent metal uptake are essential for, and immediately precede, the production of resistant spores;5 6 (ii) activation of dormant spores is associated with the partial release into the medium of DPA salts;7 (iii) germination parallels the complete release of DPA.7 8 The recent demonstration that DPA stimulates the rate of oxygen uptake from glucose oxidation in spore extracts9 and an analysis of the pathway of glucose metabolism'0 provided a basis for examining the regulatory role of DPA on spore metabolism. The present experiments were designed to classify further the basis of the DPA stimulatory effect.