COMPARATIVE KINETIC STUDIES OF PHOSPHATE‐LIMITED GROWTH AND PHOSPHATE UPTAKE IN PHYTOPLANKTON IN CONTINUOUS CULTURE1

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Abstract
A comparative kinetic study of phosphate‐limited growth and phosphate uptake was carried out in chemostat cultures of Anabaena flos‐aquae Lyng. Bréb., Ankistrodesmus falcatus (Corda) Ralfs, Asterionella formosa Hass., Fragilaria crotonensis Kitt., and Microcystis sp. Lemm. For each test organism the growth rate (μ) can be described as a function of total cell phosphorus (P), i.e. cell quota (q), or hot‐water‐extractable P (qsp).Phosphate uptake rate in each species examined was a function of external P concentration (S) and intracellular P levels. The substrate parameter for uptake (Km) remained constant at all growth rates, but the apparent maximum uptake rate (Vm') increased with decreasing μ, or q, in all test organisms. At low growth rates Vm' was greater than the calculated steady‐state uptake rate (μq) by two to three orders of magnitude because Vm' is the uptake rate at S ≫ Km and μq is the rate at S ≪ Km. The difference between Vm' and μm decreased and virtually disappeared as μ approached the physiological maximum growth rate (μm), where q = qm and S ≫ Km.An inverse relationship existed between Vm' and qsp which could be described by a function that mathematically resembles noncompetitive inhibition in enzyme kinetics. The inverse relation between Vm' and (q – q0) was described by a three‐parameter function. This empirical function provided a good description of this inverse relation over the range from Vm' at q approaching q0 up to and including calculated net, maximum uptake rates at q = qm.