Energy metabolism in Streptococcus cremoris during lactose starvation

The ATP pool of Streptococcus cremoris in a lactose-limited chemostat depletes rapidly when lactose is consumed. The decrease of the intracellular ATP concentration parallels the dissipation of the electrochemical proton gradient. The adenylate energy charge of growing cells is 0.8 but drops rapidly to 0.2 when the cells enter the starvation phase.One of the early events of lactose starvation is a rapid increase of the pools of phosphoenolpyruvate and inorganic phosphate. The accumulation of phosphoenolpyruvate is temporarily and levels off at a much lower value than in growing cells; the accumulation of phosphate is of a more permanent nature. Despite the low PEP concentration starved cells are, after 24 h of incubation in the absence of lactose, still able to take up lactose, to synthesize ATP and to generate quickly an electrochemical proton gradient.Abbreviations PEP phosphoenolpyruvateDedicated to Prof. Dr. Gerhart Drews on the occasion of his 60th birthday