Synchronous Growth of Enteric Bacteria

Abstract

Helmstetter and Cummings devised a technique of synchronization in which cells are implanted on a membrane filter and the membrane is subjected to reverse flow of liquid medium. The cells in the effluent stream have predominantly the characteristics of newborn cells. The advantage of this technique is that the population experiences a minimum of physiological stress; hence, the behavior of the synchronous culture should reflect the normal divisional cycle. The disadvantage is that strains other than Escherichia coli B/r cannot be synchronized. We have found that a modification of the method makes it possible to synchronize several strains of E. coli , including both male and female strains, as well as Salmonella typhimurium LT2. The principal difference in technique is a prolonged period (>400 doublings) of cultivation in glucose minimal medium at 30 C and at low density (<5 × 10 6 cells/ml) prior to implantation. This precaution was taken to insure that the bacterial growth population is in a steady state of balanced growth. From the resulting synchronous growth, the distribution of interdivision times has been computed; these distributions have coefficients of variation in the range 0.18 to 0.22 and are not appreciably skewed.