Recombination in Bacteria: Outcrossing Escherichia coli K 12

Abstract

THE discovery of recombination in Escherichia coli^1,2 has given to bacterial genetics a much wider scope than it had before. Three years after its first publication, however, the results obtained by Leder-berg with the strain known as K 12 still stand alone, no other bacterial strain having been found to show a similar behaviour. This is partly due to the fact that demonstration of recombination is a slow business, owing to the work required for the preparation of suitable substrains. In fact, the only method known so far is still the original one of mixing substrains having different growth requirements on a minimal medium where neither parental strain can grow, but on which cells possessing some of the synthetic capacities of one strain and some of the other will be able to form colonies. As such colonies, called by Lederberg 'prototrophs', usually appear at a very low rate, care must be taken that recombination is not simulated by back-mutation in either parental strain.