THE STEADY-STATES OF CONTINUOUS CULTURES WITH LOW RATES OF MEDIUM RENEWAL PER CELL

Continuous cultures of the chlorophyte Dunaliella tertiolecta R.W. But cher were stabilized for different sets of dilution rates d and nitrat e concentrations so in the renewal milieu. Cell concentrations at equi librium were compared to the theoretical concentrations obtained using differential equations postulated in Droop's model. The experimental data were in agreement with the theoretical when the rate of nutrient renewal per cell exceeded a certain limit R. Coupling different values of d and s(o) where the limit R is not attained - for example, low va lues of d with high value of s(o) - algal density at equilibrium is in ferior to the theoretical density. Algal mass, calculated from cell vo lume, is also inferior to theoretical mass, although to a lesser exten t. It is suggested that when the rate of renewal R (which is probably species specific) is insufficient, the population of cells is inhibite d by the emergence of unfavourable factors (e.g. insufficient eliminat ion of toxic excretion, predominant bacterial activity). In these extr eme experimental conditions, as the population is not uniquely limited by the limiting factor, the hypotheses supported by the Droop's model and the continuous culture theory become non-verifiable.