Proposed mechanism for generation and localization of new cell division sites during the division cycle of Escherichia coli.

The earliest detectable event at future sites of cell division in Escherichia coli is the appearance of paired periseptal annuli that flank the site of formation of the division septum. The development and localization of these structures were followed as the cell progressed through the division cycle. The data suggest that (i) new periseptal annuli are generated from annuli already in position at the midpoint of the newborn cell; (ii) the nascent annuli are then displaced laterally during cell elongation to positions at 1/4 and 3/4 cell length; and (iii) the annuli at 1/4 and 3/4 cell length are retained during division, becoming the midpoint annuli of the newborn cells at the sites of the forthcoming division septum. The results indicate that the sites of future divisions can be identified and committed to the division process prior to the division cycle in which these sites are utilized for septum formation, and they suggest a model in which preexisting sites of cell division generate future division sites by a replication/displacement mechanism.