Inhibition of growth of the green algaChlorella pyrenoidosa by unsaturated fatty acids

The activity of a number of unsaturated fatty acids in inhibiting the growth of the green algaChlorella pyrenoidosa has been studied using the paper disk-agar plate method. Acrylic and undecylenic acids were highly active, but other θ-unsaturated fatty acids tested were only weakly active. Oleic and elaidic acids were inactive at 0.2 M, but other C₁₈-C₂₂ acids with 2 to 6 double bonds were generally active down to a concentration of 0.01–0.005 M. Activity with chaulmoogric acid was noted down at 0.002–0.001 M. Diffusion rates of the acids through the agar seem to affect the size of the inhibition zones. The implications that polyunsaturated fatty acids may play a role in algal ecology are discussed.