Glucose excretion by the symbiotic Chlorella of Spongilla fluviatilis

Chlorella sorokiniana strain 211-40c, a symbiotic Chlorella isolated from a freshwater sponge, excreted between 3% and 5% of assimilated 14CO2 as glucose in the light, with a pH optimum around 5. This percentage increased when the illuminance was lowered (to 15% at 200 lx). Release of [14C]glucose continued in the dark and could be inhibited by the uncoupler carbonyl cyanide p-trifluoromethyoxyphenylhydrazone (FCCP). Net efflux of glucose occurred even at a concentration ratio of extracellular/intracellular glucose of 4. This, together with the sensitivity to FCCP, is taken as evidence for active transport. Exogenous [14C]glucose was taken up by the cells under conditions of net glucose efflux, showing uptake and excretion to take place simultaneously.