Coral reefs edification is based on the formation of a calcium carbonate skeleton by scleractinian corals ad on the symbiotic association that many of them establish with photosynthetic Dinoflagellates from the genus Symbiodinium. Both processes involve the transport and the use of inorganic carbon (Ci) coming from seawater for photosynthesis, and from animal metabolism for calcification. This work focused on the molecular and physiological study of poorly known mechanisms that allow the utilization of Ci in corals.
Previous physiological studies suggested different strategies in the Ci uptake between in hospite and free-living Symbiodinium. We cloned a P-type H+- ATPase gene involved in algal CO2-Concentrating Mechanisms. This gene is the first to show a symbiosis-dependent expression in the symbiont.
Carbonic Anhydrases (CAs) are key enzymes in coral physiology. This work allowed the cloning and the localization of two CAs. The first one is involved in calcification while the second one is likely to play a role in the intracellular pH regulation and the CO2 / HCO3- equilibrium. A pharmacological study of these two enzymes identified inhibitor and activator compounds that have been then used in physiology experiments. This last approach may represent a new and more accurate way of studying the role of CAs in coral physiology. This work is currently complemented by the characterization of new CA isoforms and other actors of Ci transport in scleractinian corals.
Key words: Stylophora pistillata; inorganic carbon; biomineralization; CO2- concentrating-mechanism; Carbonic anhydrase.