Cell Width inEscherichia coli: Interrogating Coupling to Nucleoid Structure

Cell dimensions of rod-shaped bacteria such as Escherichia coli are connected to mass growth and chromosome replication. It divides ≈20 min after termination of the replication cycle that initiates ≈40 min earlier at a relatively constant mass. Cells enlarge by elongation only, but at faster growth in richer media they are also wider. Width determination occurs in the divisome during the division process, coupled, temporally and spatially, to the ratio between the rates of growth and replication. The elusive signal directing the mechanism for width determination is related to the tightly linked duplications of the nucleoid (DNA) and the sacculus (peptidoglycan), the only two structures (macro-molecules) existing in a single copy. Six biologically meaningful parameters related to the key number of replication positions are reasonable candidates to convey such a signal. The current analysis discovered that of these, nucleoid complexity is the most likely parameter affecting cell width. As a corollary, a new, indirect approach to estimate replication rate is revealed.