Wirkung von aminoacridinen auf die intrazelluläre vermehrung und die auslösung von mutationen beim phagen χ von Serratia marcescens

Abstract

Zusammenfassung Development of the temperate phage χ of Serratia marcescens HY is inhibited by acriflavine (ACF), acridine yellow (AG), or proflavine (PF). When any one of these acridines is present during the entire laten periode, the mean burst size is the more reduced the higher the concentration of the dye. The size distribution of single bursts of treated and untreated infected cells indicates that this decrease is due to a reduction of the burst size in more or less all of the cells, and not to inactivation of most of the cells and a normal burst size of a few unaffected (resistant) ones. In experiments where an acridine was present only during part of the latent period and then diluted out, phage development revealed three phases of different sensitivity of acridines: During the first 20 min, inhibition occurred only at high concentrations ( e.g. 30 μg ACF/ml); between the 20th and 50th minute acridines caused only little additional inhibition; and from 50 min up to complete lysis of the culture (onset of normal lysis at about 65 min after infection) the burst size was strongly reduced even at low concentrations, ( e.g. 5 μg ACF/ml): the more so the later the dye was withdrawn. The assume that during the first phase early synthesis is affected; that the second phase represents the period of DNA replication; and that during the highly acridine sensitive third phase, maturation of phage particles is affected. This interpretation of the third phase is supported by the observation that mature phages in artificially lysed cells (without any dye) first appeared 50 min after infection. When cells were first grown at a low concentration of an acridine and then transferred to a high concentration cell division resumed after a much shorter lag than without this pretreatment. Since only 3–4 cell duplications had occurred at the low concentration, this “adaptation” is probably not due to selection of resistance mutants. “Adapted” cells did allow phage development at higher concentrations than “unadapted” ones. In untreated lysates, four types of plaque mutants of phage χ can be distinguished. Among these, one (type e) predominates. None of the three acridines when applied under various conditions increased the frequency of any of the mutants remarkably. Only b mutants showed a small significant increase. But this could be due to selection because the burst size of this mutant was less reduced by acridines than that of the wild type. The lack of mutagenicity of acridines in phage χ as compared with phage T4 could be due to the induction of mutations, mainly by affecting recombination rather than replication since in phage χ only one “round of mating” takes place (compared to five in phage T4). The burst size of e mutants is only half that of the wild-type phage. Since their frequency in a normal lysate is not changed after one growth cycle, counter selection must have been compensated for by spontaneous mutation; and, since it is not influenced by acridines, the high spontaneous frequency of e mutations must be due to a mechanism which is not influenced by acridine intercalation into DNA.