Phosphate-limited growth of Chromatium vinosum in continuous culture

Abstract

Chromatium vinosum DSM 185 was grown in continuous culture at a constant dilution rate of 0.071 h-1 with sulfide as the only electron donor. The organism was subjected to conditions ranging from phosphate limitation (SR-phosphate=2.7 μM and SR-sulfide=1.8 mM) to sulfide limitation (SR-phosphate=86 μM and SR-sulfide=1.8 mM). At values of SR-phosphate below 7.5 μM the culture was washed out, whereas SR-phosphate above this value resulted in steady states. The saturation constant (Kμ) for growth on phosphate was estimated to be between 2.6 and 4.1 μM. The specific phosphorus content of the cells increased from 0.30 to 0.85 μmol P mg-1 protein with increasing SR-phosphate. The specific rate of phosphate uptake increased with increasing SR-phosphate, and displayed a non-hyperbolic saturation relationship with respect to the concentration of phosphate in the inflowing medium. Approximation of a hyperbolic saturation function yielded a maximum uptake rate (Vmax) of 85 nmol P mg-1 protein h-1, and a saturation constant for uptake (Kt) of 0.7 μM. When phosphate was supplied in excess 8.5% of the phosphate taken up by the cells was excreted as organic phosphorus at a specific rate of 8 nmol P mg-1 protein h-1.