Rate maintenance of cell division in Escherichia coli: analysis of a simple nutritional downshift

A competitive (nonmetabolizable) inhibitor of glucose uptake, a-methylglucoside, was used to limit the growth ofEscherichia coli. Cell division during such a nutritional shift-down was studied in batch cultures and with the "baby-machine " technique. Following a brief delay, the rate of division was maintained for 60 to 70 min in batch cultures and for an extended period in the baby machine. Decreases in cell size were due, in part, to a possible reduction in the mass per chromosome origin at the time of replication initiation and a shorter time interval between initiation and the subsequent division. These unusual findings suggest that this method for abrupt change in growth rate without modifying repression patterns is useful for studying the control ofvarious aspects of the bacterial cell. A bacterial cell divides C + D min after initiation of chromosome replication (10). Initiation capacity builds up during its preceding doubling time, T min. Cell mass at initiation is, to a first approximation, 27-multiple of a mini-mal value, Mi, where n is an integer greater than or equal to (C + D)/T (5, 25). The resultant increase of cell size with growth rate, 1/, at least in Escherichia coli and Salmonell