Growth and division of Escherichia coli

Two assumptions frequently have been made in studies on the growth of individual bacteria. The increase in volume of rod-shaped bacteria has been assumed to consist of an increase only in length; thus, measurements of length have been used to estimate the volume of a cell (A. L. Koch et al., J. Gen. Microbiol. 29:421, 1962; J. F. Collins and M. H. Richmond, J. Gen. Microbiol. 28:15, 1962). Secondly, it has been assumed that the cytoplasm of the mother cell is equally divided between the two daughter cells (A. L. Koch and M. Schaechter, J. Gen. Microbiol. 29:435, 1962). We present evidence that these assumptions are substantially correct. Escherichia coli ML30 was grown for five generations in glucose minimal medium at 30 C. Cells were harvested by centrifugation, washed, and suspended in distilled water. A sample of the suspension was sprayed on Formvar-coated grids and air-dried. Electron micrographs were made with a final magnification of 20,000 X. The outlines of the cells were regular and showed no appreciable alteration of shape. Lengths and diameters of 214 cells were measured from the micrographs. If growth consists of an increase only in length, regression of diameter as a function of length should show a slope of zero. Linear regression of the data gave a slope of 0.0032 0.0099 micron