EFFECTS OF CARBOXYLIC ACIDS ON GROWTH AND PHOTOSYNTHESIS OF HAEMATOCOCCUS PLUVIALIS

The effects of a number of carboxylic acids on growth of Haematococcus pluvialis were examined at pH 5.0 and 7.5. The rate of growth at pH 5.0 was less than at pH 7.5. Of the acids examined, only glycolic and glyoxylic acids stimulated growth. A number of these acids were inhibitory, and in most cases this was more marked under acidic conditions. Malonic acid, at a concentration of 5 mM, had little effect on growth at either pH 5.0 or 7.5.The rate of photosynthesis was depressed at pH 5.0 compared with the rate at pH 7.5, but more so in the presence of malonic than succinic acid. In the malonate culture there was no accumulation of organic acids or glutamate in the cells, indicating that the activity of succinic dehydrogenase was not blocked. Malonic acid did, however, suppress the amount of carbon in the alcohol-insoluble residue, and increased the protein to polysaccharide ratio in the newly formed insoluble residue.None of the carboxylic acids examined served as a source of carbon for heterotrophic growth in the dark. Acetate and glycolate did, however, serve as a source of carbon for growth in the light under carbon dioxide free conditions. Glycolate was effective at both pH 7.5 and 5.0, but acetate was toxic at the latter pH.The minimum pH for growth of the alga was between 4.0 and 4.5. Amino acids and amides, added as a source of nitrogen for growth, were used poorly, if at all, at both pH 5.0 and 7.5.