Physiological and geometrical conditions for cell division in Escherichia coli.

During recovery of division in filaments of a temperature-sensitive DNA replication mutant, DNA-less cells were formed with a broad variation in cell lengths. It is argued that segregated nucleoids are necessary to indicate the site of division and that, in their absence, the cell has no additional mechanism to locate the division site. A second condition for division is based on geometrical arguments: the cell must be able to reestablish its original surface to volume ratio or its diameter, either of which may decrease during elongation. Electron microscopy and auto-radiography of radio-labelled sacculi prepared from E. coli MC4100 lysA, cultured in glucose minimal medium, showed that these cells elongate at a constant diameter and double their rate of surface synthesis during the constriction period.