RADIATION RESISTANCE AND GENETIC SEGREGATION IN A LARGE CELL POSSIBLY POLYPLOID STRAIN OF ESCHERICHIA COLI

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Abstract
E. coli P6 is a large cell strain obtained after camphor treatment of a purlne-requiring strain of E. coll B, designated 82/r. The results of comparative radiation sensitivity and genetic recombination tests on the two strains fortify the evidence of Ogg and Zelle that P6 may be a diploid or polyploid derivative of 82/r. P6 was found to be markedly more resistant to X-rays, gamma rays and UV. Whereas 82/r exhibited exponential survival curves following X-ray and gamma ray treatment, P6 was characterized by sigmoidal or multihit survival curves and estimated radiation target numbers corresponded to those observed in a polyploid series of yeast. P6 displayed a significantly higher frequency of prototroph formation in crosses with E. coli K-12 and E. coli B mutants than did the parent strain 82/r. The segregation of cell size and gamma ray resistance among prototrophs of crosses involving P6 were also compatible with the hypothesis that P6 may be diploid or polyploid.

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