ENVIRONMENTAL AND PHYSIOLOGICAL FACTORS AFFECTING THE UPTAKE OF PHOSPHATE BY CHLOROBIUM-LIMICOLA

The uptake of soluble phosphate by the green sulfur bacterium Chlorobi um limicola UdG6040 was studied in batch culture and in continuous cul tures operating at dilution rates of 0.042 or 0.064 h(-1). At higher d ilution rates, washout occurred at phosphate concentrations below 7.1 mu M. This concentration was reduced to 5.1 mu M when lower dilution r ates were used. The saturation constant for growth on phosphate (K-mu) was between 2.8 and 3.7 mu M The specific rates of phosphate uptake i n continuous culture were fitted to a hyperbolic saturation model and yielded a maximum rate (Va(max)) of 66 nmol P (mg protein)(-1) h(-1) a nd a saturation constant for transport (K-t) of 1.6 mu M. In batch cul tures specific rates of phosphate uptake up to 144 nmol P (mg protein) (-1) h(-1) were measured. This indicates a difference between the pote ntial transport of cells and the utilization of soluble phosphate for growth, which results in a significant change in the specific phosphor us content. The phosphorus accumulated within the cells ranged from 0. 4 to 1.1 mu mol P (mg protein)(-1) depending on the growth conditions and the availability of external phosphate. Transport rates of phospha te increased in response to sudden increases in soluble phosphate, eve n in exponentially growing cultures. This is interpreted as an advanta ge that enables Chl. limicola to thrive in changing environments.