NATURE OF ANTIBIOTIC SUBSTANCES 119 



NATURE OF ANTIBIOTIC SUBSTANCES 



It has already been established that antagonistic actinomycetes read- 

 ily produce a variety of different types of antibiotic substances. Some of 

 these have been isolated and even crystallized and information has been 

 gained concerning their chemical nature. Others have been obtained in 

 the form of crude but highly active preparations. Still others are known 

 but they have not been isolated as yet and have, therefore, been rather 

 insufficiently studied. So far, eight substances have been definitely 

 recognized: actinomycetin, actinomycin, streptothricin, streptomycin, 

 proactinomycin, micromonosporin, litmocidin, and mycetin. 



Among the various antagonistic actinomycetes, five species have 

 been studied in detail and, therefore, deserve particular attention, 

 namely, S. antibioticus (974), S. lavendulae (979), 5. griseus (830), 

 A'', gardneri (313), and S. albus (1000). 



S. antibioticus produces a highly active antibiotic substance that has 

 been isolated and described as actinomycin. It was shown to be antago- 

 nistic to all species of bacteria tested as well as to many fungi (Table 

 19). Actinomycin is not affected by heat. It is soluble in ether and in 

 alcohol as well as in other solvents, but in water only in very high dilu- 

 tions. It is highly toxic to animals. 



Several species of actinomycetes are capable of producing actinomy- 

 cin in both organic and synthetic media, the yield varying with the or- 

 ganism (955a, 1002a). The addition of 0.25 per cent agar to stationary 

 cultures increases considerably the growth of the organism and the pro- 

 duction of actinomycin. The presence of a small amount of starch, phos- 

 phate, and sodium chloride was also found to be favorable. Actinomy- 

 cin-producing forms are strictly aerobic, and are able to produce actino- 

 mycin only when grown either in very shallow layers or under aerated 

 or agitated submerged conditions. 



S. lavendulae is capable of inhibiting the growth of many gram- 

 negative and gram-positive bacteria. It produces an antibiotic substance 

 designated as streptothricin. 



For the production of streptothricin, the tryptone can be replaced by 

 a variety of simple nitrogenous compounds, such as glycine (Table 

 20), alanine, aspartic acid, asparagine, and glutamic acidj the carbo- 



