112 MOLECULES, VIRUSES, AND BACTERLV 



the Other materials were calcium ions and a spore peptide. The occur- 

 rence of dipicolinic acid was of special interest because it was the first 

 time this chemical had been reported in a natural product. A follow-up 

 of these studies has shown that dipicolinic acid is a normal constituent 

 of all spores of bacteria (both aerobes and anaerobes), and that it is 

 present in considerable quantities, varying from 6 per cent to 12 

 per cent of the dry weight of normal spores. As soon as these announce- 

 ments were made, all the workers in spore research examined their 

 spores for this chemical and were able to confirm the observation of 

 Powell. 



Further studies on this chemical have brought out a number of 

 interesting points in connection with the physiology of the bacterial 

 spore. Nearly all the dipicolinic acid is released into the outside 

 medium when the spores germinate. The release of this acid correlates 

 almost perfectly with the loss in heat resistance, the loss in refractility, 

 and the gain in stainability; this provides good circumstantial evidence 

 that dipicolinic acid plays an essential role in the unique heat-resistant 

 properties of spores. Studies made on the activation of the dormant 

 enzymes through heat shock, germination, or mechanical rupture also 

 show a very good correlation between the release of the dipicolinic 

 acid and the activation of these enzymes (Murty and Halvorson, 

 1957b). This gives further circumstantial evidence for the importance 

 of dipicolinic acid in the protection of these enzymes in the intact spore. 

 The acid is also released from the spores when they are killed by heat 

 (Lund, personal communication). This fact has been demonstrated in 

 a number of laboratories. The temperature that is required is dependent 

 upon the heat tolerance of the spores themselves. For instance, the 

 spores of thermophilic organisms must be heated to a higher tempera- 

 ture to release the dipicolinic acid than those of some less resistant 

 aerobic organisms. In a recent announcement, Foster (1959) reported 

 that dipicolinic acid can be released from spores of Bacillus mega- 

 terium at temperatures ranging from 70° to 100° C. As the temperature 

 is increased, less time is required. 



These numerous observations have led investigators in this area of 

 study to believe that spores are made heat-resistant and their enzymes 

 are protected by a complex collodial structure involving a polymer 

 formed from dipicolinic acid, calcium, and special peptides. It would 

 be interesting indeed to know more about the nature of this complex. 

 So far it has remained obscure, because no means has yet been found 

 to rupture the spore and retain the complex. Any form of mechanical 

 rupture breaks up the complex and releases the dipicolinic acid in the 

 same way that germination does. The breaking of this complex during 

 germination may well be an enzymatic process, and the enzymes may 

 be activated by mechanical rupture as well, so that when spores are 



