Physiological characteristics of chemostatically grownCitrobacter freundii as a function of the specific growth rate and type of nutrient limitation

Abstract

Citrobacter freundii was grown aerobically in a chemostat on a mineral medium witn galactose or glucose as carbon and energy sources under limitation by carbon or nitrogen source respectively. At various specific growth rates ranging from 7 to 95% μ_max the culture in steady state was analysed and growth yield, specific metabolic rate of substrate utilization, intracellular concentration of pyruvate, ATP, ADP, AMP and energy charge were determined and plotted as functions of dilution rate. In all four types of experiments the physiological state of cells remained practically independent of dilution rate up toD = 0.6 μ_max, and at a given specific growth rate nearly independent on μ_max and type of limitation. At approximatelyD = 0.6 μ_max, which is close to the maximum output dilution rateD _m, the physiological state of the cells changed: growth yields decreased and intr cellular pyruvate and adenylates concentrations increased. Consequently, in a given medium two dilution rates exist at which growth rate dx/dt is the same but the physiology of the population is quite different.