DIFFERENTIATION BETWEEN RADIATION-SENSITIVE AND -RESISTANT MUTANTS OF ESCHERICHIA COLI, STRAIN B

Abstract

Morphological heterogeneity in cell sizes of Escherichia coli, strains B, B/r, and BSprevents estimation of the viable cell count by the indirect turbidimetric method. The average dry weights of E. coli B, B/r, and BS, when grown in acetate synthetic medium, are 0.16, 0.10, and 0.13 picograms per cell respectively. Increased radiation sensitivity was correlated with those bacterial populations showing decreased intracellular glycogen content, decreased lipopolysaccharide–lipoprotein content, R-colony forms, and cellular elongation. The radiation-sensitive strains contained more DNA, RNA, and protein per cell than the radiation-resistant mutant; however, no significant differences were evident in the DNA, RNA, and protein contents on a dry weight basis. No qualitative differences in the monosaccharides or their derivatives were found. Intracellular glucose synthesis and accumulation preceded DNA, RNA, and protein synthesis throughout the lag and early logarithmic growth phases for all three strains. Multiple forms of intracellular glycogen complexes were present in all three strains. In addition to unbound glycogen and protein-bound glycogen, a bound form of glycogen was consistently associated with crude fractions which contained the DNA, RNA, and lipopolysaccharide constituents. Increased lability of the cold TCA-insoluble bound glycogen to hot TCA and alpha-amylase hydrolysis was correlated with increased radiosensitivities of the organisms.