Isolation, Growth, and Physiology of Acidophilic Chlamydomonads¹,²

SUMMARY A buffered, chelated, defined medium was developed for isolation and growth of acid‐bog flagellates and for physiological studies of bog chlamydomonads. Hydrogen ion tolerances of Chlamydomonas acidophila, C. sphagnophila 121 A, C. sphagnophila IU293, and, C. reinhardi were determined. Only C. acidophila grew at pH 2.0. It did not grow at pH 7.0 or 8.0 as did the other chlamydomonads tested. Liver fraction “L” and Fe permitted growth of C. acidophila at pH 2.0 equal to control growth at pH 5.0. Neither C. sphagnopliila 121A nor C. reinhardi grew at pH 2.0 with these additions. Hydrogen ion seems to be excluded from the cell interior of acid‐tolerant species. They remained green ( ie, pheophytinization did not occur) when cultured below pH 5.0. C. acidophila grew in the dark with glucose as sole source of carbon and energy. Acetate, glycolate, and glyoxylate were assimilated in the dark if glucose was also present. C. sphagnophila 121A did not grow in the dark on any of the 51 organic carbon compounds tested. C. acidophila and C. sphagnophila 121A seem promising tools for determining biochemical mechanisms responsible for differences in H + tolerances. Presumably specialized cell walls or membranes are involved.