A CONTINUOUS CULTURE STUDY OF PHOSPHATE UPTAKE, GROWTH RATE AND POLYPHOSPHATE IN SCENEDESMUS SP.1

Abstract

SUMMARYThe kinetics of phosphate uptake and growth in Scenedesmus sp. have been studied in continuous culture with particular reference to the shifts in the cellular P compounds as a function of growth rate.Uptake velocity is a function of both internal and external substrate concentrations and can be described by the kinetics of noncompetitive enzyme inhibition. The concentrations of polyphosphates (alkali‐extractable or 7‐min) can he substituted as inhibitors in the kinetic equation. The apparent half‐saturation constant of uptake. Km, is 0.6 μM. The apparent half‐saturation concentration for growth is less than Km, by 1 order of magnitude. Growth is a function of cellular P concentrations, and the polyphosphates (alkali‐extractable or 7‐min) appear to regulate growth rate directly or indirectly. To understand P limitation, therefore, it is necessary to measure both external P and internal polyphosphate levels. Evidence indicates that alkali‐extractable polyphosphates, which can be quantitatively determined by a simple method of measuring surplus P, are involved in cell division process find that a maintenance concentration of functional phosphate exists in the form of poly phosphates. Alkaline phosphatase activity has an inversely linear relationship to growth rate and to the reciprocals of both polyphosphates and surplus P. Changes in lipid P, RNA P, and presumably all other forms except DNA are related to changes in growth rate.