An investigation of adhesion and detachment in slime mould amoebae using columns of hydrophobic beads

Vegetative amoebae of Dictyostelium discoideum (strain AX2) adhere to columns of hydrophobic beads (Bio-Beads SM-2) which have been coated with axenic growth medium. This binding is blocked by sodium azide and other inhibitors of aerobic respiration. Bound cells are not detached by lowering the temperature but they can be eluted from the column by including azide in the medium. However, this effect is critically influenced by temperature. The elution profiles become progressively shallower as the temperature is lowered. The profiles represent a set of probability distributions whose means and variances increase with decreasing temperature. Below 20 degrees C, the mean time to cell detachment is a linear function of temperature. A statistical model of this azide-stimulated detachment has been developed which closely predicts the real data. It assumes that each amoeba has k binding sites whose stochastically independent behaviour is governed by a parameter theta; the mean time to detachment of each site is 1/theta. Both parameters have been estimated. The value of k is close to 3 and does not vary with temperature below 20 degrees C. In contrast, theta varies in such a way that the value of 1/theta increases linearly with decreasing temperature, so paralleling the behaviour of the mean cell detachment time.