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Abstract
Summary: Mutuants of Escheriachia coli were induced by u.v. light and selected by the criterion that they formed small colonies on a nutrient agar at normal temperature. Nine slow-growing mutant strains were isolated. These mutants were characterized and compared during exponential growth in a nutrient medium with respect to doubling time, average cell mass, and DNA and RNA contents. The mutants showed only two groupings of doubling times, approximately 60 min and 35 min, as compared with 20 min for the parent. The Mutants were heterogeneous with regard cell mass, ranging from considerably larger than the parent to smaller. There was no constancy between average cell mass and the population doubling time. RNA:mass and DNA:mass ratios were similar among mutant strains with the same doubling time despite large variations in average cell mass.
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