EFFECT OF THE TEMPERATURE OF GROWTH OF ESCHERICHIA COLI ON THE FORMATION OF BETA-GALACTOSIDASE.

Marr, Allen G. (University of California, Davis), John L. Ingraham, and Craig L. Squires. Effect of the temperature of growth of Escherichia coli on the formation of beta-galactosidase. J. Bacteriol. 87:356-362. 1964.-The synthesis of beta-galactosidase was measured during exponential growth of Escherichia coli in a succinate-minimal medium over a temperature range of 10 to 43 C for the following: (i) a constitutive strain, and (ii) an inducible cryptic strain, induced maximally with isopropyl-thio-beta-d-galactopyranoside (IPTG), or induced submaximally with IPTG. The differential rates of synthesis of beta-galactosidase were identical for the constitutive strain and for the fully induced strain; the rates were constant from 20 to 43 C, and decreased progressively with a decrease in temperature below 20 C. Thus, in the absence of specific repression, the ability of E. coli to produce beta-galactosidase decreases at low temperature. The differential rate of the submaximally induced culture was minimal between 20 and 30 C, and increased progressively with temperature both above 30 C and below 20 C. That the repressor concentration is maximal at 20 C was established by measuring the rate of induced synthesis of beta-galactosidase as a function of the concentration of IPTG; the relative concentrations of repressor were 1.00:3.28:0.25 at 40, 20, and 10 C, respectively. After an abrupt change in temperature, the differential rate of a submaximally induced culture changed gradually to the rate of the steady state, which is in agreement with the proposal that the effect of temperature is on the concentration of repressor and not on the equilibrium between repressor and its site of action. The effect of temperature on catabolic repression was determined by comparing the differential rate of synthesis of beta-galactosidase by a constitutive strain grown in succinate-minimal medium with the rate in glucose-minimal medium at various temperatures; the ratio of the rates in the two media decreased progressively and approached 2.0 as the temperature of growth was increased.