| Abstract: | Bacteriostatic doses of 5-methyltryptophan and of 7-azatryptophan exert a complete inhibition on the in vitro production of filtrable hemolysin by Escherichia coli. This inhibition is readily overcome by L-tryptophan, and does not seem to be specific but secondary to an interference with de novo protein synthesis and cell multiplication as is observed with chloramphenicol in sensitive strains. Although the influence of the two tryptophan analogs on hemolysin production and cell multiplication is similar, their mechanism of action at the molecular level appears to be different. The addition of 50 µg/ml 7-azatryptophan which causes an unbalanced growth characterized by an arrest of the cellular division and an increase of cell size, blocks the production of an active hemolysin. Exposure to 4 µg/ml 5-methyltryptophan also prevents cell multiplication and hemolysin production but no sign of unbalanced growth is evident. Mitomycin C in concentrations sufficient to prevent increase in the number of viable units provokes an extreme elongation of E. coli cells and, apparently, does not stop the synthesis of hemolysin. In blocking the production of hemolysin the three inhibitors of protein synthesis used in this study were more effective than mitomycin C an agent known to affect deoxyribonucleic acid synthesis and to induce extrachromosomic genetic factors. Results of conjugation experiments also described here support the finding of other workers that the genetic factor that controls the production of the filtrable hemolysin in E. coli can be transmitted by conjugation. Acridine orange eliminated the hemolytic property from a large proportion of the population of a hemolytic strain which did not carry the R factor, but was little effective in the strains which had received both the R factor and the hemolytic character by conjugation. |
