UC San Diego

Escherichia coli, the most thoroughly studied model organism, is a rod- shaped bacterium that elongates at an exponential rate relative to its length. Recent studies have suggested that E. coli cells contain regions that are inert; that is, they do not contribute to the elongation of the cell. It is likely that these regions are mostly contained in the semispherical poles of the cell. Using the formulas for the idealized geometry of an E. coli cell (a cylinder plus two semispheres), I derived models for the exponential elongation of the cell. To test the validity of each model, I collected length data over time from growing E. coli cells and fit the data to the models. The data best fit a model in which E. coli cells contain inert regions of length equal to two times the radius of the cell, which is the combined length of the poles of the cell. The data thus present evidence in support of the existence of inert polar regions of E. coli cells