I.VrK" MlCll ANISMS 



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a t'r(^sli culttii-c of S. grisciis, j)hafi;(' nuilti|)li- 

 cation was ohtaiiicd. After six transfers, I'acli 

 pliaiic particle inci'eased to 7") X 10'"". I'liaf2;e- 

 resistant strains \\(>re I'eatiily isolated; sneh 

 enltures retained tluMr capacity to pi-oduce 

 streptomycin Iml wvvv not al)solntel>- fi-ee 

 from phaii;(\ 



To obtain acti\'e phages, a .']- to ."j-day-old 

 sliaken cnlture of a streptomycin-producinji; 

 strain of N. (irisciis is filtered aseptically 

 through paper and inocuhUxnl on i)lates. A 

 given phage preparation is inoculated into 

 the young cultures, allowed to incuhate foi' 

 24 to 72 hours, and filtered through a Seitz 

 filter. Dilutions of phage, ranging from 1 : 10'' 

 to 1:10'- are added to 10-ml l)ortion^; of the 

 sterile nutrient agar, previously inoculated 

 with 0. 1 -ml portions of the paper-filtered cul- 

 ture; the agar is poiu'ed into plates; these are 

 incubated at 28°C for 2 days. The plaque 

 counts are then made and calculated for 1 

 ml of culture. Some preparations gave 4 X 

 10"' or more particles per milliliter (Koerber 

 et al., Walton). 



Reilly c( al. reported that actinophage at- 

 tacks only the streptomycin-producing 

 strains of S. griseus. Xo efTect was obtained 

 on streptomycin-producing organisms other 

 than S. griseus. Strains of S. griseus that did 

 not produce streptomycin did not allow 

 phage multiplication; the phage may thus 

 actually be destroyed or adsorbed. 



The actinophage of S. griseus multiples 

 only on living cell material and not on the 

 heat-killed material of this organism. The ac- 

 tinophage has an optimum temperature for 

 nniltiplication at 28°C. It does not multiply 

 at 37°C or above. Actinophage can withstand 

 a temperature of 75°C for 1 houi-, but is 

 completely destroyed at 100°C in 10 min- 

 utes. Actinophage can be stored at (3°C with- 

 out loss of activity, but storage at 28°C or at 

 higher temperatures results in a loss of ac- 

 tivit.v, the rate of loss being proportional to 

 the increase in temperature. The phage is 

 more rapidly destroyed in organic media 



'I'aiu.h 13 



l\[licl of (iildilioii of pltiKjv upon pliiujc iiiiill I pi Icu- 



lioii (Hid streptoiin/cin prodiiclion htj different 



slrrplonii/ces in slationary cuUureii (Reilly, 



Harris, and Wak.smati) 



* Each 60-ml flask of culture received at start 

 0.1 ml of M-1 phage, amounting to 7 X 10' par- 

 ticles per milliliter of medium. 



than in water. It is also inactivated in acid 

 media. It was suggested, therefore, that a 

 phage-infected culture of an actinomycete be 

 grown in an acid medium to free the culture 

 from the phage. The action of phage takes 

 place best in organic media; very little or no 

 action is obser\'ed in synthetic media. 



Other antibiotic-producing streptomyces 

 are also subject to attack by specific phages. 

 This is true, for example, of the chlortetra- 

 cycline-producing S. aureofaciens (Weindling 

 and Karpos). 



