Section 5 — Mutagenesis 



tagen-treated phages on the bacterial cell were 

 recently reported. Thus, these were mutations 

 found in the descendants of the phages treated. 

 Induced phage mutations arising directly after 

 the treatment of bacteriophages were also 

 reported. There are no reports, however, on 

 such cases with actinophages, nor are there 

 reports on obtaining induced mutations in 

 actinophages in general. 



The authors of the present work tried to obtain 

 mutations in extracellular actinophages by 

 exposing them to mutagens and to reveal 

 mutations immediately after the treatment of 

 phages with mutagens. For this purpose the 

 authors used an actinophage belonging to the 

 phage group that affects streptomycin producing 

 cultures. H-mutations were studied. As the host 

 cultures sensitive strain A. streptomycini B-6 

 and resistant strain A. streptomycini No. 675 

 were used. Spontaneous frequency of H-type 

 mutations in our phage was 1 per 10 3 of all 

 inoculated corpuscles. As mutagens u. v. -light, 

 nitrous acid and sarcolysine hydrochloride were 

 used. 



Repeated tests have shown that sarcolysine 

 hydrochloride pronouncedly increases the fre- 

 quency of H-type mutations which exceeded in 

 some experiments the frequency of spontaneously 

 occurring mutations byor der 2 or 3, whereas 

 u.v.-light and nitrous acid did not produce any 

 notable increase of the mutation frequency. 



Thus, it was the first case of obtaining induced 

 mutations in actinophages and, what is more 

 important — in extracellular actinophages. 



Further studies of sarcolysine as a mutagen 

 were carried out with several derivatives of this 

 preparation which differed from sarcolysine 

 hydrochloride in an additional amino acid 

 chain. A number of polyfunctional chlore- 

 thylamines were also studied. 



The fact that all the mutagens used cause 

 mutations in extracellular actinophages may 

 serve as a ground for a new interpretation of the 

 mode of phage mutation. 



5.6. The Action of Some Mutagenic Agents on 

 Bacteriophage 0X-174. J. H. van de Pol 

 and G. A. van Arkel (Utrecht, The Nether- 

 lands) 



The inactivation of bacteriophage OX-174 with 

 nitrous acid (Tessman, 1959) and ultraviolet 

 rays (Setlow and Boyce, 1960) follows a single- 

 hit kinetics. It has also been found for the inac- 

 tivation of T4 with hydroxylamine by Freese and 

 coworkers (1961). We likewise found for 0X-174, 

 when treated with nitrous acid and ultraviolet 



rays, an inactivation curve that was single-hit. 

 Upon treatment of the phage by hydroxylamine, 

 however, an inactivation curve was obtained 

 that extrapolated at zero time to approximately 

 2. In contrast to expectations the inactivation of 

 OX-174 by hydroxylamine thus appears to be 

 a double-hit event. Results will be presented of 

 experiments performed in order to test possible 

 explanations of the curves. 



Another notable finding was that the in- 

 activation constant depended on the way the 

 phage was grown, presumably on the medium 

 used for propagation. The nature of this differ- 

 ence in sensitivity will be discussed. 



The mutagenic action of hydroxylamine was 

 studied by determining the number of host 

 range mutants appearing on C/0S, a phage- 

 resistant mutant of E. coli C (Van de Pol, 

 Vendrig and Van Arkel, 1963; cf. Van Arkel and 

 Van de Pol, these abstracts). A method has been 

 developed for the detection of the induced 

 mutants. The number of mutants was measured 

 as a function of the dose, and was compared to 

 the values calculated assuming either single- or 

 double-hit kinetics of mutagenesis. 



The effect of mutagenic agents on isolated 

 0X-DNA and on double-stranded phage DNA is 

 under investigation. 



5.7. Synergistic Mutational Effects Between Radi- 

 ations and Chemicals. Delbert M. Shankel 

 (Lawrence, U.S.A.). 



When cells of Escherichia coli are impinged on 

 membrane filters, subjected to nonlethal dosages 

 of ultraviolet light and subsequently incubated 

 in media containing certain chemicals, e.g. 

 caffeine, theophylline, theobromine, a great 

 increase in mutant numbers occurs. This increase 

 is much greater than the total obtained from the 

 two treatments employed separately. These 

 "synergistic" effects of the chemicals can be 

 prevented partially by the inclusion of very 

 small amounts of other chemicals such as 

 cysteine or 2-animo,4-sulfonamido-phenyl-disul- 

 fide in the post-irradiation phenotypic expression 

 medium. The synergistic activity of the caffeine- 

 type compounds appears to be related to certain 

 features of their chemical structure. The amount 

 of ultraviolet dosage plays a crucial role in the 

 synergistic effect; nonlethal dosages providing 

 for the maximal synergistic effect, while in- 

 creasing dosages result in the gradual disap- 

 pearance of the synergistic activity. Radioactive 

 tracer experiments indicate that the synergistic 

 chemicals are not incorporated into the nucleic 

 acids of the cells. No synergistic relationship 



57 



