Modified method of application of ethyl methanesulfonate for induction of Escherichia coli mutants.

An efficient modification of ethyl methanesulfonate mutagenic action is based on mutagenization of small volumes of cell suspensions in micro-sample tubes. This provides for a rapid and safe handling of solutions of cancerogenic mutagens. A 3-4-h exposition to 30-40 mmol/L of mutagen appeared optimal, inducing more than 20% auxotrophs or, after a simultaneous application of the penicillin method, 60% of auxotrophs. Moreover, the modification proved its value in repeated applications of ethyl methanesulfonate, resulting in an accumulation of various mutation types. Consecutive mutations were accompanied by an increase in sensitivity. Based on the distribution of nucleoids in the mutagenized population, the penicillin method was modified to allow detection of mutants segregated from cells with several nucleoids.