A metabolic model for acetate uptake under anaerobic conditions by glycogen accumulating organisms: Stoichiometry, kinetics, and the effect of pH

A metabolic model for the stoichiometry of acetate uptake under anaerobic c onditions by an enriched culture of glycogen accumulating organisms (GAOs) was developed and tested by experimental studies. Glycogen served as the so urce of both reducing power and energy to drive the process of acetate upta ke. The amount of glycogen consumed and poly-beta -hydroxyvalerate (PHV) ac cumulated in the cells increased with increasing pH, indicating that the en ergy requirements for acetate uptake increased:with pH. The composition of the accumulated poly-beta -hydroxyalkanoates (PHAs) was adequately predicte d using the assumption that acetyl-CoA and propionyl-CoA condense randomly to produce PHA. In addition, the rate of acetate uptake was strongly affect ed by the pH. The rate decreased with increasing pH and this dependence cou ld be described with a saturation type of expression. A comparison of the r ate of acetate uptake at low pH with the rates observed in enriched culture s of phosphorus accumulating organisms (PAOs) indicated that GAOs are able to compete effectively with PAOs in nutrient removal systems under certain conditions. (C) 2001 John Wiley & Sons, Inc.