ZINDER AND LEDERBERG 



225 



CELL COUNT 



Fig. 1. Assay of FA. FA (LT-2) and cells (LA-22) were mixed at various dilutions 

 and plated on minimal agar. Prototrophs were counted after 48 hours. 



tivate FA was of particular interest. 

 Enzymatic activity was verified by 

 testing samples of the reaction mixture 

 for reduction of the viscosity of thy- 

 mus nucleic acid (kindly supplied by 

 Dr. R. D. Hotchkiss). Similar controls 

 were not done for the other enzymes. 



Evocation of FA. The properties of 

 phages latent in Salmojiella have been 

 summarized by Burnet and McKie 

 (1929) and Boyd (1951). Lysogenic 

 phages, i.e., those obtained from lyso- 

 genic bacteria, poorly lyse sensitive 

 cultures and readily provoke second- 

 ary resistant lysogenic forms. Visible 

 lysis of sensitive cells is observed only 

 at low multiplicities of infection. With 

 higher multiplicities there is little evi- 

 dence of lysis. When phage is added 

 to broth cultures, the tube does not 

 clear, and the bacteria grow at a re- 

 duced but significant rate. PLT-22 is 

 typical of these phages. 



To determine whether PLT-22 was 

 unique in its FA evoking activity, a 



variety of treatments was applied to 

 resting and growing cells of LT-2 

 strains. FA was not detected in the 

 filtrates of young cultures or after 

 autolysis with benzene, extraction of 

 dried cells, treatment with high con- 

 centrations of antibiotics (penicillin, 

 bacitracin, and aureomycin), or com- 

 plete phage lysis. Dilute antibiotics, 

 lithium chloride, and crystal violet 

 yielded variable FA. High activity is 

 most readily detected in the filtrates of 

 cultures treated with lysogenic phages. 

 These results indicate that FA is not 

 released by mechanical, chemical, or 

 biological disruption of cells. How- 

 ever, various deleterious agents elicit 

 its appearance in a way that may 

 parallel the action of latent phage. The 

 most effective concentrations of these 

 reagents were those which only 

 slightly inhibited the cells. FA has also 

 been detected in aged cultures when 

 autolysis sets in. This may be due to 

 the action of mutant lysogenic phage. 



