Diameter of cells of a thermosensitive dnaA mutant of Escherichia coli cultivated at intermediate temperatures.

Strains of Escherichia coli K-12 carrying the dnaA46 mutation exhibited a progressively decreasing DNA concentration and a progressively increasing cell size as the temperature was raised from 31 to 37 degrees C. Above 37 degrees C, steady-state exponential growth could not be maintained. The increase in average cell size with increasing growth temperature was due to an increase in cell length. There was no change in cell width. This seems to rule out the hypothesis that the increase in cell width in thy strains cultivated on low concentrations of thymine is due to the decrease in DNA concentration which also occurs under these conditions.