SUMMARY: F donor bacteria were treated with u.v. radiation, mitomycin C, nitrous acid, hydroxylamine or caffeine, and then incubated for various periods in broth at 37° before conjugation. U.v. radiation, mitomycin C and nitrous acid increased the fertility of F populations, but hydroxylamine and caffeine did not. The maximal effect of u.v. irradiation was obtained after using a dose 50-100 ergs/mm. and after 45 min. incubation in broth of irradiated bacteria before conjugation. The maximal effect of mitomycin C occurred after treatment with 1-3 μg./ml. and after 110 min. incubation in broth. Depending on the strain used, the fertility of the population increased 8-20 times after u.v. irradiation and 5-21 times after mitomycin C. The effect of u.v. irradiation could be photoreactivated up to 50%. Following treatment of strain 1655 with nitrous acid (0.01 ), a three- to four-fold increase in the yield of conjugation was obtained, although irregularly. Caffeine (0.01%) enhanced the effect of u.v. irradiation about two-fold. Chloramphenicol blocked the expression of the effect of u.v. irradiation and mitomycin C. The effect of chloramphenicol was not permanent, because after its removal followed by further incubation the fertility of the F population increased to the same degree as in the samples in which the bacteria, previously exposed to u.v. radiation or mitomycin C, were incubated in broth without chloramphenicol.


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