PHOTOSYNTHESIS OF ZOOCHLORELLA CELLS ISOLATED FROM FRESH-WATER BAIKALSPONGE LUBOMIRSKIA-BAICALENSIS

Photosynthetic characteristics were examined in symbiotic zoohlorella cells isolated from the fresh-water sponge Lubomirskia baicalensis col lected from Lake Baikal. Photosynthesis was saturated at a light inten sity of about 20 W/m2. Maximum gas exchange rates were observed at 30- degrees-C both in light and in darkness. Measurements of the rate of C O2-dependent oxygen evolution showed that freshly isolated zoochlorell a has a low affinity for CO2, which increased upon cell adaptation to air. The half-saturation constants for all soluble inorganic carbon fo rms, measured at different pH, suggest that CO2 is the principal carbo n form transported into the cell. At low pH, zoochlorella cells can ex crete up to 40% of the assimilated carbon into the external medium.