X-Ray Induced Mutant Strains of Escherichia Coli

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Abstract
Following a 2d x-ray treatment with 180,000 r of 2 mutant strains of E. coli, 16 new mutant strains have been obtained from 1,741 single colony isolations. One mutant strain was obtained from 1,902 isolations from unirradiated material. 14 of the strains required single known growth factors in addition to the requirement of the strain from which they were derived for biotin or for threonine. The growth factors required by these strains include proline, glutamic acid or proline, leucine, isoleucine, phenylalanine, methionine, cystine, histi-dine, thiamin and thiazole. 3 strains required unidentified substances present in yeast extract. The 10 mutants derived from the biotin-requiring strain all required biotin, and in the 7 mutants from the strain requiring threonine, the original requirement also persisted. The specificity of the requirements was tested by substituting biochemically related substances. Thus there are, for instance, 2 types of mutants requiring thiamin; one type can utilize thiazole instead, the other can not. The results are said to be consistent with the theory that growth-factor requirements in bacteria result from hereditable changes analogous to the true gene mutations of Neurospora.

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