Establishment of exponential growth after a nutritional shift-up in Escherichia coli B/r: accumulation of deoxyribonucleic acid, ribonucleic acid, and protein

Abstract

The accumulation of DNA, RNA and protein was followed in cultures of E. coli B/r during exponential growth in different media and for 2 h after a nutritional shift-up from succinate minimal medium (growth rate [.mu.1] = 0.67 doublings/h) to glucose plus amino acids medium (.mu.2 = 3.14 doublings/h). During postshift growth of the culture, the amounts of RNA (R), DNA (D) and protein (P) increased such that the ratios of the increments (.DELTA.R/.DELTA.P; .DELTA.D/.DELTA.P) were constants (k1, k2). This implies that the rates of accumulation of nucleic acids and protein form time-invariant ratios; i.e., (dR/dt):(dD/dt):(dP/dt) = k1:k2:1. These constants change from their preshift value to their final postshift value (i.e., k1 and k2) within a few minutes after the shift. k1 is a function of the activity of ribosomes, but k2 is related to the initiation of rounds of DNA replication. These parameters and the observed change in the doubling time of RNA (= .mu.2/.mu.1) were used to derive kinetic equations that describe the accumulation of DNA, RNA, protein and cell mass during the 2-3 h transition period after a shift-up. The calculated kinetics agree closely with the observed kinetics.