Studies of algal antibiosis using Haematococcus and Chlamydomonas

Five common freshwater algae were grown in the ten possible two‐membered combinations. No two species grew as well in mixed cultures as they did separately. One combination, Haematococcus‐Chlamydomonas, was selected for more detailed study. When grown together in the same container, Haematococcus pluvialis and Chlamydomonas reinhardi were found to be incompatible. The latter invariably dominated the cultures, usually within 3–5 days after inoculation. The rate at which Chlarmydomonas eliminated Haematococcus was influenced by a number of factors, the most important being light intensity and nitrogen source. Inhibition of Haematococcus was due to a fat‐like extracellular substance that was soluble in alkaline medium, somewhat heat stable, and steam distillable from an acid medium. The inhibitor was produced by Chlamydomonas and liberated upon the death of the cells. It is suggested that the inhibitor is probably a long‐chain fatty acid or mixture of such acids. Eight long‐chain, unbranched, saturated, and unsaturated fatty acids of known composition were assayed against six algae. Palmitic was the most toxic saturated acid tested, linoleic the most toxic unsaturated. Haematococcus was the most sensitive alga tested, Chlorella and Scenedesmus the least sensitive. There was a relatively narrow range of concentrations between those causing no inhibition and complete inhibition in the case of Haematococcus. The results of the present study are compared with those from other investigations of algal antibiosis.