20 A. L. PlERSTORFF 



and Hill (1921), Waksman (1922), Bayliss (1924), or Waksman and 

 Davison (1926) should be consulted. Waksman and Davison (1926: 

 L08-114) list the enzymes whieh are produced by bacteria as: catalase, 

 cytase, diastase, emulsin, hemolysins, gelase, invertase, lipase, lactase, 

 maltase, meliases, pyocyanase, oxidases (tyrosinase and luciferase), 

 proteases (gelatinase and casease), reductases, rennet, urease, and prob- 

 ably an enzyme similar to erepsin which causes bacteriophage. Most 

 of the information concerning bacterial enzymes does not relate to 

 phytopathogenic species. However, the enzymes secreted by phytopatho- 

 genie fungi have received considerable attention from plant pathologists 

 in studies on parasitism. 



In an effort to throw more light on the food requirements and patho- 

 genicity of Bacillus amylovorus, a study of the enzymes produced by 

 this organism in artificial media was made. 



It is a well-known phenomenon that apple shoots are susceptible to 

 attacks of B. amylovorus as long as meristematic tissue is forming, 

 and that as soon as the terminal bud forms the shoots can be repeatedly 

 inoculated with only occasional infection. Experimentally, the host 

 can be placed at the temperature for optimum growth of the parasite, 

 abundant water can be supplied, and still no infections may occur. 

 A possible explanation is that some chemical change has taken place 

 within the host which has made it impossible for the parasite to get 

 food through the action of its enzymes. For example, the phloridzin 

 content of apple twigs as determined by Harvey (1925) shows a close 

 parallel with growth processes. The presence or absence of this 

 compound may be one of the influencing factors in susceptibility or 

 resistance. 



Since enzymes cannot be defined in chemical terms and can be detected 

 in a medium only by the products formed, this method of determining 

 their presence was used. If a given product was split by a culture of 

 B. amylovorus and such a cleavage did not occur in the uninoculated 

 check, it was assumed that this change was brought about by an enzyme 

 produced by the bacteria. The pH and temperature requirements, the 

 influence of the presence or absence of certain salts, the production 

 of extracellular and intracellular enzymes, and the fact that certain 

 enzymes may be unstable or inactivated in the absence of their substrate 

 or products of their reaction, was carefully considered in each case. 



All cultures used for enzyme tests were adjusted to optimum ranges 

 of pH for the respective enzymes, unless otherwise noted. It was 

 noticed that alkaline cultures tended to become more acid, and acid 

 cultures more alkaline. This was especially true of the bouillon and 

 pectic compound cultures. 



