G.J.J. Kortstee

Regulation of polyphosphate metabolism in Acinetobacter strain 210A grown in carbon- and phosphate-limited continuous cultures

The response of Acinetobacter strain 210A to low phosphate concentrations was investigated in P- or C-limited chemostat cultures. The organism accumulated poly-β-hydroxybutyric acid under P-deprivation, at phosphate concentrations ranging from 0.1 to 0.7 mM. The amount of biomass was proportional to the phosphate concentration in the medium and no polyphosphate was formed. When shifting a culture from P- to C-limitation phosphate was accumulated as polyphosphate. No poly-β-hydroxybutyrate could be detected in these cells. The amount of polyphosphate in the cell showed a hysteresis. When cultures were shifted from low to high phosphate concentrations, polyphosphate reached a maximum of about 60 mg P per gram of dry weight at about 3 times excess phosphate (ca. 2.5 mM Pi). It decreased to 45 mg P per gram dry weight at approximately 5 times the phosphate needed for growth (ca. 3.5 mM Pi). In the reverse case (high to low) polyphosphate did never exceed 45 mg P per gram dry weight. The specific activities of alkaline phosphatase and the phosphate uptake system were induced at residual Pi concentrations below the detection limit (<10 μM). The specific uptake rate followed also a hysteresis. The specific activities of polyphosphatase and polyphosphate: AMP phosphotransferase increased when polyphosphate formation was possible.

Polyphosphate formation by Acinetobacter johnsonii 210A: effect of cellular energy status and phosphate-specific transport system

Abstract In acetate-limited chemostat cultures of Acinetobacter johnsonii 210A at a dilution rate of 0.1 h−1 the polyphosphate content of the cells increased from 13% to 24% of the biomass dry weight by glucose (100 mM), which was only oxidized to gluconic acid. At this dilution rate, only about 17% of the energy from glucose oxidation was calculated to be used for polyphosphate synthesis, the remaining 83% being used for biomass formation. Suspensions of non-growing, phosphate-deficient cells had a six- to tenfold increased uptake rate of phosphate and accumulated polyphosphate aerobically up to 53% of the biomass dry weight when supplied with only orthophosphate and Mg2+. The initial polyphosphate synthesis rate was 98 ± 17 nmol phosphate min−1 mg protein−1. Intracellular poly-β-hydroxybutyrate and lipids served as energy sources for the active uptake of phosphate and its subsequent sequestration to polyphosphate. The H+-ATPase inhibitor N,N′-dicyclohexylcarbodiimide caused low ATP levels and a severe inhibition of polyphosphate formation, suggesting the involvement of polyphosphate kinase in polyphosphate synthesis. It is concluded that, in A. johnsonii 210A, (i) polyphosphate is accumulated as the energy supply is in excess of that required for biosynthesis, (ii) not only intracellular poly-β-hydroxybutyrate but also neutral lipids can serve as an energy source for polyphosphate-kinase-mediated polyphosphate formation, (iii) phosphate-deficient cells may accumulate as much polyphosphate as activated sludges and recombinants of Escherichia coli designed for polyphosphate accumulation.

Ecological aspects of biological phosphorus removal in activated sludge systems

Inorganic polyphosphate (poly-P) is a linear polymer of many tens or hundreds of inorganic phosphate (Pi) residues linked by high-energy phosphoanhydride bonds (Fig. 1) and usually consists of mixtures of different molecular sizes. Thermodynamically the standard free energy of hydrolysis of the anhydride linkage yields about 38 kJ per phosphate bond at pH 5. The energy storage function of poly-P depends on the ability of the bond cleavage reaction to effect phosphorylation and thereby conserve the energy associated with the hydrolytic action (Dawes, 1990).

Polyphosphate-accumulating bacteria and enhanced biological phosphorus removal

More than 50 years ago, Jeener and Brachet (1944) observed that addition of inorganic phosphate (Pi) to a suspension of yeast cells previously subjected to phosphate starvation induced massive accumulation of a basophilic substance within the cells. Soon afterwards this substance was isolated and identified as inorganic polyphosphate (polyP) (Schmidt et al.1946; Wiame 1948). This was by no means the first isolation of polyP from a microorganism. As early as 1888 Liebermann had obtained polyP from yeast, probably metaphosphate. Over the next 50 years hardly any paper on this polyP from yeast appeared. The work of Wiame and others marks the beginning of biological research on inorganic polyP.