Growth and physiology of potassium-limited chemostat cultures of Paracoccus denitrificans

Abstract

In potassium-limited chemostat cultures of Paracoccus denitrificans the maximum specific growth rate (µmax) was found to depend on the input potassium concentration: At 0.21mM µmax was 0.10–0.11 h-1; at 0.44 mM 0.15–0.16 h-1 and at 0.66 mM 0.20–0.21 h-1. The plots of the specific rates of oxygen-, succinate-and potassium consumption against μ gave straight lines. The intracellular potassium concentration was a linear function of μ and varied from 1% (0.13 M) at a μ value of 0.034 h-1 to 2.2% (0.29 M) at μ=0.26 h-1; the potassium concentration gradient and the potassium concentration in the culture fluid in the steady state were dependent on the input potassium concentration. The potassium concentration gradient varied from 8,900-1,200. At all μ values 20–25% of the total energy production was used for potassium transport. 350,100 and 30 ATP molecules were calculated to be required to maintain one potassium ion intracellular during 1 h at μ values of 0.034, 0.197 and 0.257 h-1 respectively. It is concluded that the amount of circulation of potassium is dependent on the potassium concentration gradient or on the potassium concentration in the culture in the steady state. The dependency of µmax on the input potassium concentration was explained by the assumption that at low input potassium concentrations the net uptake of potassium (influx-efflux) is not rapidly enough to maintain the high potassium gradient in the existing cells and to establish it in the newly formed cells. At high μ values and at high input potassium concentrations µmax is limited by the specific rate of oxygen consumption, which was found to be 11–12 mmol O2 g dry weight-1 h-1 at µmax for potassium-, succinate-and sulphate-limited chemostat cultures.