Nutrient uptake kinetics and growth of zooxanthellae maintained in laboratory culture

Abstract

Growth characteristics and nutrient uptake kinetics were determined for zooxanthellae (Gymnodinium microadriaticum) in laboratory culture. The maximum specific growth rate (μmax) was 0.35 d-1 at 27 °C, 12 hL:12 hD cycle, 45 μE m-2 s-1. Anmmonium and nitrate uptake by G. microadriaticum in distinct growth phases exhibited Michaelis-Menten kinetics. Ammonium half-saturation constants (Ks) ranged from 0.4 to 2.0 μM; those for nitrate ranged from 0.5 to 0.8 μM. Ammonium maximum specific uptake rates (Vmax) (0.75 to 1.74 d-1) exceeded those for nitrate (0.14 to 0.39 d-1) and were much greater than the maximum specific growth rate (0.35 d-1), suggesting that ammonium is the more significant N source for cultured zooxanthellae. Ammonium and nitrate Vmax values compare with those reported from freshly isolated zooxanthellae. Light enhanced ammonium and nitrate uptake; ammonium inhibited nitrate uptake which was not reported for freshly isolated zooxanthellae, suggesting that physiological differences exist between the two. Knowledge of growth and nutrient uptake kinetics for cultured zooxanthellae can provide insight into the mechanisms whereby nutrients are taken up in coral-zooxanthelae symbioses.