Frequency of Recombination in E. coli K 12

Abstract

ACCORDING to the technique introduced by Lederberg¹ and generally adopted, the cross between two bacterial strains differing in growth-factor deficiencies is carried out by means of mixing on “minimal medium”² suspensions of young cultures of the two strains, which have been washed by centrifugation twice in saline. In the course of research in this Department, we observed that if instead crosses are made between the first supernatant liquids, which are usually thrown away, the ratio of prototrophs to parental cells is many times greater.