Environmental and physiological factors affecting the uptake of phosphate by chlorobium limicola

The uptake of soluble phosphate by the green sulfur bacterium Chlorobium limicola UdG6040 was studied in batch culture and in continuous cultures operating at dilution rates of 0.042 or 0.064 h-1. At higher dilution rates, washout occurred at phosphate concentrations below 7.1 &mgr;M. This concentration was reduced to 5. 1 &mgr;M when lower dilution rates were used. The saturation constant for growth on phosphate (K&mgr;) was between 2.8 and 3.7 &mgr;M. The specific rates of phosphate uptake in continuous culture were fitted to a hyperbolic saturation model and yielded a maximum rate (Vamax) of 66 nmol P (mg protein)-1 h-1 and a saturation constant for transport (Kt) of 1.6 &mgr;M. In batch cultures specific rates of phosphate uptake up to 144 nmol P (mg protein)-1 h-1 were measured. This indicates a difference between the potential transport of cells and the utilization of soluble phosphate for growth, which results in a significant change in the specific phosphorus content. The phosphorus accumulated within the cells ranged from 0.4 to 1.1 &mgr;mol P (mg protein)-1 depending on the growth conditions and the availability of external phosphate. Transport rates of phosphate increased in response to sudden increases in soluble phosphate, even in exponentially growing cultures. This is interpreted as an advantage that enables Chl. limicola to thrive in changing environments.