CHEMICAL CHANGES DURING SPORE GERMINATION 81 



properties are common to all spores? We have all had experience enough 

 to agree that not all the spores, even in a single clone, are resistant; so 

 resistance per se could not be accepted without considerable rationalization. 

 Furthermore, not all bacterial spores are germinatable by methods by which 

 the bacteriologist can detect germination, so we cannot use as a definition 

 of a spore: a cell that can germinate. Also, not all bacteria we ordinarily 

 regard as competent in this matter do form spores under conditions which 

 are physiologically homogeneous and where other clonal members do spor- 

 ulate. Hence, conditions for sporulation have no absolute implications for 

 our definition. Not all spores are heat activatable, and those which are 

 respond differently to different temperatures. I will admit that I thought the 

 Illinois group had a clue to the answer when they came up with the alanine- 

 alanine racemase story. But they did too nianv experiments and the hope 

 for general applicability of this feature is not as sustaining now as it ap- 

 peared to be when that work was first reported. 



One could extend this list, but presently, and I advisedly use the term 

 "presently," the only things I know to be common to all bacterial spores 

 are (1) they are produced inside another cell, and (2) they all contain dipi- 

 colinic acid. The first of these requires no additional comment. What about 

 dipicolinic acid, which so far as my knowledge goes, has not been found 

 absent in any of the aerobic or anaerobic spores thus far tested. It being 

 present in surprisingly high percentage in the resistant form of the bacterial 

 cell and undetectable in the non-resistant vegetative form, and the fact that 

 it has not been recorded as occurring in any other biological system, make 

 it very easy to ascribe a preponderant, if not compelling, importance to this 

 compound in the underlying mechanisms of resistance. Although I see no 

 serious objection to this assumption, it is nevertheless worth emphasizing 

 to you the state of our information on this subject by the reminder that 

 the evidence for a direct role of dipicolinic acid in resistance can only be 

 regarded as circumstantial. Other possibihties, such as its representing a 

 metabolite of amino acid metabolism similar to the analogous pipecolic acid 

 in other systems, could be eliminated if we had more specific information 

 on the function of dipicolinic acid. Are there any other substances, unique 

 or common, present in significant amounts in spores? A host of other ques- 

 tions could be asked, but they devolve to one: this biologically unique com- 

 pound probably has some special significance for the known properties of 

 spores. 



The work of Dr. Curran and of Dr. Powell, indicating an unusual concen- 

 tratibn of calcium in spores, naturally focusses attention upon a relation 

 between this cation and dipicolinic acid. This question became all the more 

 attractive when work in Dr. Powell's laboratory suggested that dipicolinic 



