Calorimetrie Study of Escherichia coli Growth on Bouillon Medium

Heat evolution during the growth of Escherichia coli in a stationary culture on bouillon medium was continuously monitored with a conduction-type batch calorimeter at different pHs and temperatures. The growth thermograms were found to be reproducible within percent errors of ±2.1%, ±0.8% and ±1.5% for the peak time of a thermogram, the peak height and the total heat evolution, respectively. The mean heat evolution for the formation of a unit E. coli cell was co = (1.69 ±0.08) X 10^—8 J cell^{— 1} at pH 6.2 and 37°C. The mean heat evolution rate per unit cell during growth was _1, which was consistent with values calculated for other microbial cells. The growth rate constant calculated on kinetic analysis of the growth thermograms was μ = 0.532 ± 0.068 hr ^-1 at pH 6.2 and 37°C. The pH dependence of the growth rate constant showed that the growth activity of E. coli cells on bouillon medium is maximum in the pH range of 5.5 to 6.5. From the temperature-dependent variations in the growth rate constant, the apparent activation energy of E. coli growth was found to be E_a =65.3 ±7.1 kJ mol^-1.