The Coupling of Phosphate Accumulation to Acid Production by a Non-growing Streptococcus

Abstract

SUMMARY: Accumulation of phosphate by washed, stored suspensions of stationary phase streptococcal strain SL-1 is strictly energy-dependent, essentially unidirectional and coupled stoichiometrically to acid production. At saturating concentrations of extracellular glucose and phosphate, incubation at varying pH values alters the rates of phosphate accumulation and concomitant fermentation of glucose such that coupling remains intact. Extracellular pH, while not affecting the coupling of phosphate accumulation to acid production, determines the total capacity for accumulation of phosphate and consequently the point of uncoupling of these processes. The conditions of cell storage profoundly affect the pH dependency of phosphate accummulation. During phosphate accumulation, the intracellular o-PO4 pool contracts by more than 50 %. About half of the accumulated phosphate appears in a high molecular weight fraction (i.e. insoluble in cold HClO4) under conditions which contraindicate net nucleic acid synthesis, protein synthesis or the incorporation of exogenous glucose carbon into high molecular weight cell constituents. The data are consistent with the hypothesis that stationary phase streptococcus SL-1 synthesizes inorganic polyphosphates.