106 



THE ACTIXOMYCETES, Vol. I 



were changes of a cultui'al and morpho- 

 logical nature; fewer changes of a physio- 

 logical and biochemical nature; and no 

 change in the antibiotic nature of the organ- 

 isms. This is cjuite at variance with the 

 above reports on the production of mutants 

 from the streptomycin-producing S. griseus 

 and streptothricin-forming S. lavendulae. 



Mutations 



The concept of "mutation" and the usage 

 of this term has led to a particular contro- 

 \'ersy. The term has been applied to "sudden 

 changes which are neither the result of a 

 process d gradual acclimatization or educa- 

 tion ror of selective isolation." In recent 

 years the subjects of mutations and varia- 

 tions among microorganisms have gained 

 new impetus from studies on the nutrition 

 of the organisms, involving growth factors 

 and metabolites, formation of antibiotics, 

 and development of resistance to a given 

 antibiotic to which they were originally sen- 

 sitive. 



The formation of mutiuits by actinomy- 

 cetes has long been recognized. These were 

 considered as special types of ^^ariants. The 

 formation of new strains through the muta- 

 tion of a culture, however, is more fimda- 

 mental and hereditary. White strains were 

 obtained from blue-pigmented forms; strains 

 free from aerial mycelium, from those pro- 

 ducing such mycelium; red strains, from 

 orange-yellow forms. These mutations were 

 accompanied by changes in morphological, 

 cultural, and physiological charactei's which 

 differentiated the new strains from the 

 mother cultui'(\'<. The differences thus ob- 

 tained may l)e so distinct as to give the new 

 strain a characteristic of a species. 



Krassiluikov and his collaborators made 

 a detailed study of such stable mutants. 

 They emphtisized that the \'ariations or 

 mutations take place from the simpler to the 

 more complex forms, as from micrococci to 

 mycobacteria, fioin mycobacteria to no- 



cardias, and from nocardias to streptomyces ; 

 the reverse phenomenon occurs but seldom. 

 This reasoning led Krassiluikov to the con- 

 clusion that actinomycetes are present in 

 natural substrates, such as soil, largely in the 

 form of micrococci. Kedrovski, however, 

 emphasized that the reverse is true, actino- 

 mycetes giving rise to rod-shaped forms of 

 the tuberculosis type. 



Spontaneous mutations in stored spores of 

 streptomyces were studied by Wainright. 



Saltations 



x\mong the mutations, the phenomena of 

 saltations occupy an important place among 

 the actinomycetes (Rippel and Witter). 

 They are similar in natiu'e to those occurring 

 in colonies of fungi or bacteria. New forms 

 appear in a colony either as sectors or as 

 daughter colonies. These sectors may differ 

 from the mother colony by the presence or 

 absence of aerial mycelium, by a change in 

 color of the substrate or aerial mycelium, by 

 structure or rate of growth of the colony, by 

 presence or absence of "fairy rings," etc. 

 (Lieske, Kriss, Krassiluikov). These sal- 

 tants, upon careful transfer to fresh media, 

 will produce new stable varieties; they differ 

 from the original species in their morpho- 

 logical, physiological, or cultural properties. 

 Some of these saltants could easily be desig- 

 nated as different species had their origin 

 not been known. 



Schaal found as many as nine sectors in a 

 single colony of S. scabies. The cultures ob- 

 tained from these sectors \^aried in the nature 

 of the mycelium, in the rate of growth, and 

 in the pigmentation. The formation of spirals 

 and the direction of the turns in the spirals 

 were also variable characters. Nutrition 

 exerted a marked effect: production of aerial 

 mycelium was inhibited by a high nitrogen 

 content of the medium; ])resence of thiamine 

 favor(>d rapid growth and the formation of 

 sectors. There was no correlation, Iiow(>\-er. 



