PHOSPHATE-UPTAKE BY ZOOXANTHELLAE ISOLATED FROM CORALS

[P-32]orthophosphate was used to study phosphate uptake by Symbiodinium sp. isolated from the hermatypic coral Acropora formosa. The results for phosphate uptake are uniphasic and obey Michaelis-Menten kinetics. The value for the Michaelis constant (K(m) was 14-mu-M. Phosphate uptake was dependent on light. Preincubation of freshly isolated zooxanthellae in the presence of 500-mu-M phosphate caused a significant decrease in uptake capacity. These results suggest that the zooxanthellae in this study originate from conditions where phosphate is depleted. The results are discussed in relation to the depletion-diffusion hypothesis for nutrient uptake in zooxanthellate symbiosis.