ZINDER AND LEDERBERG 



et ai, 1951). These "large bodies" 

 formed mixed floccules with added 

 bacterial cells. 



Treatment of Salmonella with FA- 

 eliciting phage or penicillin results in 

 the formation of chains after one and 

 one-half hours of incubation, and by 

 three hours only "snakes" with swol- 

 len bulbular central portions are pres- 

 ent (Fleming et al., 1950). Debris and 

 small granules are also seen. FA has 

 also been produced by this time. The 

 supernatants of these cultures were 

 difficult to sterilize by conventional 

 means. Filtration through eight or 

 fourteen pound test Mandler candles 

 resulted in filtrates with a viable count 

 of about 100 per ml. Comparable fil- 

 trates of untreated cultures have regu- 

 larly proven to be sterile. Sintered py- 

 rex "UF" filters were found to be 

 suitable for sterile filtration of active 

 filtrates. 



These observations are reminiscent 

 of the L-forms of bacteria particularly 

 as interpreted by Klieneberger-Nobel 

 (1951), Dienes and Weinberger 

 (1951), and Tulasne (1951). There" is, 

 however, no evidence of a functional 

 relationship between L-forms and 

 transduction. We have not yet suc- 

 ceeded in obtaining L-colony growth 

 from our cultures that would permit 

 more direct tests, nor have other 

 workers made genetic analyses of L- 

 type growth to fortify speculations on 

 their role in a life cycle. 



Sources a?id range of activity of FA. 

 FA has been defined thus far as a spe- 

 cific product of strain LA-2 with the 

 single capacit\' of transducing a par- 

 ticular mutant of LT-22. However, 

 other direct crosses involving LA-2 2 

 had given prototrophs. To determine 

 if FA could be obtained from other 

 strains, a simplified test was applied, 

 involving the selection of streptomycin 

 resistant prototrophs, "SRP" (Leder- 

 berg, 1951a). SW-435 (LA-22 SO was 



227 



grown in mixed culture with each of 

 fifty different wild type (streptomycin 

 sensitive prototrophs) S. typhijmiriiim 

 strains, and the mixture plated on mini- 

 mal agar containing 500 mg per L of 

 streptomycin. Twenty-eight of the 

 crosses yielded evident recombinants, 

 showing that FA could probably be 

 produced by many strains. 



FA has been isolated from each of 

 twenty-five tested strains of S. typhi- 

 muriuni w^hen the proper stimulus was 

 found. PLT-22 served for the many 

 strains susceptible to it, which prob- 

 ably explains the success of the SRP 

 crosses, while other lysogenic phages 

 (from the Lilleengen series) stimu- 

 lated other strains resistant to PLT-22. 

 In general, inoculation of 10^ cells of 

 5. ty phiinuriiim and 10^ to 10^ par- 

 ticles of a lysogenic phage to which it 

 is susceptible into 10 ml of fresh broth 

 will yield FA after four hours of in- 

 cubation. Penicillin in low concentra- 

 tions (one to five units per ml) was 

 successful for some cultures. 



A demonstration of recombination 

 in Salmonella was initially sought and 

 found in terms of the recovery of pro- 

 totrophs from mixed platings of auxo- 

 trophs. A more complete proof of 

 typical sexualitv^ would depend upon 

 the occurrence of new combinations 

 of "unselected markers" (Lederberg, 

 1947). SW-478 (LA-22 Gal- Xyl- 

 iMtl-, SO was crossed with SW-414 

 (LA-2 Gal+, Xyl + , Mtl + , SO on 

 EML agar containing one of the vari- 

 ous sugars so that one unselected fer- 

 mentative character could be scored 

 directly on the cross plate. Of some 

 20,000 prototrophs screened, none dif- 

 fered from SW-478 except in their 

 nutrition. In addition to mutational 

 differences, LA-22 and LA-2 differed 

 intrinsically in ability to utilize malate, 

 alanine, or succinate as the sole carbon 

 source required for growth. All of the 

 prototrophs resembled LA-22. With a 



