306 PRINCIPLES OF SOIL MICROBIOLOGY 



Species differentiation. For a study of cultural and biochemical 

 characteristics of the organisms, a group of media may be recom- 

 mended, which will help to bring out the salient features. 



1. Synthetic media, as described above: 



(a) Modified Czapek's agar 



(b) Krainsky's glucose agar 



(c) Malate-glycerin agar (Conn) 



(d) Citrate-glycerin agar (Conn) 



Temperature of incubation 25°, period of incubation 7 to 15 days. 



2. Gelatin, 15 per cent in distilled water, reaction unadjusted; temperature 

 of incubation 16° to 18°; period of incubation 30 days. 



3. Sterile skimmed milk; temperature of incubation 25° and 37°; observations 

 made daily. 



4. Potato plug, 25°, for 7 days. 



5. Starch agar, 25°, 10 to 15 days (test for diastatic strength). 



6. Nutrient peptone agar, 25°, 7 to 15 days. 



General morphology to be studied by direct examination of colony on plate by 

 means of low power. For detailed study, the method of Drechsler to be used, 

 magnification 1000 to 1200. 



The cultural characteristics of actinomyces in these media make pos- 

 sible the suggestion of the following tentative key for their differentia- 

 tion, until a more permanent one based on morphological studies can 

 take its place. 



KEY TO THE IDENTIFICATION OF SPECIES OF SOIL ACTINOMYCES 



(Based chiefly on physiological characteristics) 



A. Formation of a soluble pigment on all media containing protein substances: 

 I. Pigment deep brown (chromogenus types): 



1. A brown pigment is produced on tyrosine agar: 



(a) Pigment dark brown; white to cream-colored growth on 



synthetic media; soluble brown pigment on synthetic 

 media containing arabinose, glucose or lactose 



A. scabies 



A number of strains of Actinomyces were isolated from 



potato scab lesions; it was suggested that there is no 



justification for including all these organisms in one 



species. 58 * 



(b) Pigment faint brown; sulfur-yellow soluble pigment on 



creatinine solution; aerial mycelium on glucose agar is 

 ocher to reddish ocher colored A. olivochromogenus 



&8a Millard, VV. A., and Burr, S. A study of twenty-four strains of Actino- 

 myces and their relation to types of common scab of potato. Ann. Appl. Biol., 

 13:580-644. 1926. 



