THE FORMATION OF SPORES BY BACTERIA HI 



an interesting enzyme, because it was active in the intact spore and 

 was heat-resistant, withstanding temperatures up to 100° C. Upon more 

 careful study we found that the enzyme remained heat-resistant even 

 after the spores germinated. Furthermore, this enzyme was attached 

 to some colloidal particles. Upon separation from the carrier by means 

 of sonic oscillation, it became heat-sensitive. 



These observations stimulated us and others to look for more en- 

 zymes in spores. Prior to this time most bacteriologists had assumed 

 that spores were devoid of enzymes, because most studies had resulted 

 in negative findings. A variety of enzymes similar to the racemase have 

 now been found in the spores of aerobic bacilli (Lawrence, 1955; 

 Nakata, 1956). A heat-resistant catalase is present in most aerobic 

 spores, and also a heat-resistant ribosidase— an enzyme which hydro- 

 lyzes adenosine into adenine and ribose. Ribosidase has also been 

 shown to be associated with a collodial particle; the heat-resistant 

 catalase, however, does not appear to be particulate. There is strong 

 evidence to suspect the existence in spores of other heat-resistant en- 

 zymes, particularly proteolytic enzymes ( Levinson, 1957 ) . These may, 

 in fact, be the ones responsible for the -changes occurring during stor- 

 age and also during heat shock, for if these are like racemase, they will 

 not be destroyed by the temperatures used for heat sensitization, and 

 the reactions they bring about may be materially speeded up at these 

 higher temperatures. 



\^arious dormant enzymes have since been found to exist in spores, 

 in addition to those mentioned abo\'e. These become activated when 

 the spores germinate or are ruptured mechanically. In the dormant 

 state they must be resistant to heat, because such enzymes can be 

 found in spores which are germinated after heating. In fact, it appears 

 from the work of Church and Halvorson ( 1955 ) that a higher activity 

 may be obtained from spores exposed to heat shock than from un- 

 heated spores. Although these enzymes are resistant to heat in the dor- 

 mant state, they cire heat-sensitive after germination and after me- 

 chanical rupture of the spores. The mechanisms involved in conferring 

 heat resistance on spores also appear to render them inactive. 



The third observation I mentioned above— namely, that spores con- 

 tain the chemical dipicolinic acid— also has proved to be a very power- 

 ful stimulus to researchers in spore physiology. This observation, as 

 well as the one concerning the heat-resistant enzymes, was a natural 

 consequence from Hills' early discovery. Powell and her co-workers 

 (1953-54), while studying germination, detected a number of organic 

 compounds which had been secreted during the process. They then 

 proceeded to examine the supernatants from germinated spore sus- 

 pensions, and they discovered that dipicolinic acid, along with other 

 materials, was released from the spores during germination. Among 



