Mutation or Variation ofEscherichia coliwith Respect to Growth Requirements

Abstract

Nine mutant strains of E. coli were obtained by single-colony isolation from cultures which had been transferred serially in a broth medium with and without x-ray treatment. A synthetic medium, capable of supporting growth of the parent strain, fails to support growth of a mutant strain without the addition of a particular growth factor. 8 of these strains appear to have lost the ability to synthesize nicotinamide, thiamine, methionine, lysine, cystine, arginine, threonine or tryptophane. One strain with less sharply defined growth requirements grows in the presence of either glycine or serine. Although the mutant strains occasionally revert to the parent strain, the rate of reversion is not great enough to interfere seriously with the use of these strains as test organisms.