Correlation Between Rate of Cell Growth and Rate of DNA Synthesis in Escherichia coli B/r

The rates of cell growth and of DNA synthesis have been measured in synchronized cultures of Escherichia coli B/r growing with three different doubling times, from 27 to 80 min. Cell volume was found to increase linearly over the cell cycle, the rate of increase doubling at a precise cell age for each growth rate. The time at which the rate of cell growth doubled was also found to be the time at which new rounds of DNA synthesis were initiated. However, it was found that these two events could be separated in time by inhibiting DNA synthesis for a short period by the addition of nalidixic acid. It is concluded that neither event is the direct trigger for the other.