CHAPTER 10 



Lytic Mechanisms 



Lysis of microbial cells in general and of 

 actinomycete cells in particular comprises a 

 nmnber of reactions, some of which fre- 

 quently are considered as enzymatic proc- 

 esses. These can be classified into three 

 groups: (a) autolytic reactions, in which the 

 growing cells, at a certain stage of their de- 

 velopment, undergo lysis; (b) bacteriolytic 

 processes, whereby certain complex mechan- 

 isms involving also enzymatic reactions 

 produced by actinomycetes have the capac- 

 ity to dissolve the cells of various bacteria, 

 living or dead; (c) sensitivity of actino- 

 mycetes to phages, designated as acti- 

 nophages and specific for each organism. The 

 first two groups of lytic reactions, or those of 

 autolysis and bacteriolysis, are known to oc- 

 cur not only among bacteria and actinomy- 

 cetes, but also in yeasts and filamentous 

 fungi. The sensitivity to phages, however, is 

 characteristic, so far as we now know, of only 

 bacteria and actinomycetes. 



Actinomycetes also possess certain other 

 lytic mechanisms. It is sufficient to mention, 

 for example, the ability of various forms to 

 cause the lysis of red blood cells. The anti- 

 biotics produced by actinomycetes may 

 bring about reactions involving lysis of vari- 

 ous microorganisms; these mechanisms fall 

 into a group by themselves and are treated 

 in detail in Chapter 15. 



Autolysis 



One of the most characteristic properties 

 of various actincjmycetes is their ability to 



undergo lysis. The animal pathogens were 

 the first to receive consideration for their 

 capacity to lyse at certain stages of growth. 

 Later, this phenomenon was shown to hold 

 true also for plant pathogens. Finally, some 

 of the soil saprophytes were found to pos- 

 sess the same property. 



The mechanisms responsible for the proc- 

 esses of autolysis among actinomycetes 

 have been variously called lysins, autolysins, 

 actinolysins. Dimitriev first described, in 

 1934, the phenomenon of lysis among patho- 

 genic actinomycetes isolated from actino- 

 mycosis of man. The capacity for lysis of 

 actinomycete colonies grown on nutrient me- 

 dia was studied by Dimitriev and Firinkov, 

 who came to the conclusion that this ca- 

 pacity is proof of the bacterial nature of ac- 

 tinomycetes. 



Dimitriev and Souteeff (1936) later re- 

 ported that when an actinomycete culture, 

 grown on agar media, underwent lysis, the 

 phenomenon was associated with the forma- 

 tion of a certain type of colony. Two types 

 of daughter colonies were produced as a re- 

 sult of lysis: one was similar to the mother 

 colony and characterized by its capacity for 

 lysis; the other did not lyse and was morpho- 

 logically different from the first. The cul- 

 tures originating from the colonies capable of 

 undergoing l.ysis were strongly proteolytic 

 and produced no aerial mycelium. The non- 

 lysing colonies yielded cultures that were less 

 proteolytic; they fornKxl a chalky white aer- 

 ial mycelium; the reaction of the medium 



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