Waksman — 76 — Actinomycetes 



ScHAAL (387) has recently shown by means of sectoring of S. scabies 

 strains that as many as nine sectors appeared in a single colony. The 

 sectors varied in the nature of their mycelium, in the rate of growth of 

 the culture, and in pigmentation. Thus the variants showed not only 

 differences in physiological characteristics from that of the parent cul- 

 ture, but even in morphology. The formation of spirals and the direc- 

 tion of turns varied with the culture. There was little variation, how- 

 ever, in the size of the cells. 



The effects of nutrition were particularly marked. Production of 

 aerial mycelium was inhibited by a high nitrogen content of the medium. 

 The presence of thiamine favored rapid growth of the cultures and pro- 

 duction of sectors. 



Various cultures of S. scabies isolated from diseased potatoes differed 

 considerably in their pathogenicity. There was no correlation, how- 

 ever, between the pathogenicity and the cultural characteristics of the 

 strain. The variants obtained from a given culture also differed from 

 the mother culture in their pathogenicity to potatoes. 



Thomas (421) isolated six physiologic races of S. scabies which 

 distinctly differed in pathogenicity on ten different potato varieties or 

 selections. The most favorable sources of carbon for the growth were 

 sucrose, cellulose, inulin, and maltose. Increasing the nitrogen, phos- 

 phorus, and potash content of the medium retarded the production of 

 aerial mycelium. Nitrogen and phosphorus were generally favorable 

 for growth; potash tended to retard it. The different races also showed 

 marked variation in their sensitivity to antiseptics and to extracts of the 

 mycelium of certain fungi. Maximum growth and stability were ob- 

 served on peat soil; mineral soils tended to retard or inhibit growth and 

 increase variability in the races studied. The more pathogenic races 

 were most stable on most media. Some variant types were peculiar to 

 individual races, but certain types were produced frequently by several 

 races, which pointed to a close genetic relationship between those races. 



These variations make one wonder, therefore, whether the many 

 species described (298) as causative agents of potato scab represent dis- 

 tinct species or only variants of one type of culture. 



Another important economic group of actinomycetes, namely, the 

 organisms producing antibiotics, show marked variation in culture. 

 Several variants were obtained from S. grisetis. They differed morpho- 

 logically in formation of aerial mycelium, and physiologically in produc- 

 tion of streptomycin, formation of acid, rate of glucose consumption, 

 autolysis, and production of pigment. Intermediary variants were also 

 obtained. 



The freshly isolated streptomycin-producing strain of S. grisetis 

 formed typical aerial mycelium, characteristic of the species. It 

 changed the reaction of a glucose-containing medium to alkaline, pro- 

 duced characteristic types of surface and submerged growth, underwent 

 only limited lysis, and was markedly resistant to the antibiotic action of 



