Chemical Changes Occurring During 

 Spore Germination 



Joan F, Powell 



Microbiological Research Department, Ministry of Supply, 

 Porton, Wiltshire, England 



IN OUR STUDIES of spore germination, we have taken loss of heat resistance 

 as the criterion of germination (Wynne and Foster, 1948). Early 

 studies showed that loss of heat resistance was associated with more 

 readily measurable changes such as decreased refractive index and increased 

 permeability to stains (Powell, 1950). In subsequent studies we therefore 

 assessed germination by nephelometry or by examination of stained films. 

 We found that while the above changes were taking place the germinating 

 spore excreted solid material equivalent to 30 percent of its dry weight into 

 the medium, at the same time swelling slightly (Powell and Strange, 1953). 

 This excretory process occurred when germination took place in a medium 

 containing only the specific germination stimulant, or in a nutrient tryptic 

 digest broth, or spontaneously in water suspension as a result of heat activa- 

 tion (Powell and Strange, 1953). The composition of the excreted material, 

 the "germination exudate," was remarkably similar in all the Bacillus species 

 we examined. 



Composition of the Germination Exudate 



The most striking common property of germination exudates w^as their 

 strong and characteristic ultraviolet absorption. The substance responsible 

 for this absorption was isolated from germination exudates of B. megaterium 

 and identified (Powell, 1953) as the calcium salt of pyridine-2:6-dicarboxylic 

 acid (calcium dipicolinate) . Calcium dipicolinate accounted for 50 to 60 

 percent of the dry weight of germination exudates and therefore repre- 

 sented approximately 15 percent of the dry weight of resting spores. We 

 have observed the ultraviolet absorjition spectrum of calcium dipicolinate 

 in extracts from disintegrated resting spores of B. megaterium, B. subtilis, B. 

 cereus, B. polymyxa, B. sphaericus, and also of Clostridium sporogenes, CI. 

 tetani, CI. histolyticum, and CI. septicum. 



The remainder of the germination exudate consisted of free amino acids, 

 peptides, and small amounts of protein. A non-dialyzable peptide of char- 

 acteristic constitution and of molecular weight in the region of 10,000 was 

 invariably present (Strange and Powell, 1954). This peptide represented 



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