Section: New Results

Bacterial growth inhibition by acetate

High concentrations of organic acids such as acetate inhibit growth of Escherichia coli and other bacteria. This phenomenon is of interest for understanding bacterial physiology but is also of practical relevance. Growth inhibition by organic acids underlies food preservation and causes problems during high-density fermentation in biotechnology. The development of new approaches for the relief of growth inhibition by acetate during high-density fermentation of E. coli is one of the motivating assumptions for the work of IBIS in the IPL project COSY (Sections 7.2 and 6.8 below).

What causes growth inhibition by acetate? Classical explanations invoke the uncoupling effect of acetate and the establishment of an anion imbalance. During his PhD thesis, Stéphane Pinhal investigated an alternative hypothesis: the perturbation of acetate metabolism due to the inflow of excess acetate. In an experimental and modelling study published in the Journal of Bacteriology [23], Stéphane Pinhal, Delphine Ropers, Hans Geiselmann, and Hidde de Jong developed a set of isogenic strains that remove different parts of the metabolic network involved in acetate metabolism. Analysis of these strains revealed that the inflow of acetate accounts for 20% of the growth-inhibitory effect through a modification of the acetyl phosphate concentration. While the study does not provide a definite answer to the question of what accounts for the remaining 80% of the reduction in growth rate, some of the observations argue against a prominent role of uncoupling in growth inhibition by acetate in the conditions tested.