Meeting Abstract
Tropical reef-building corals obtain most of their energy in the form of reduced carbon provided by endosymbiotic algae (dinoflagellates of the genus Symbiodinium). However, during times of physiological stress, for example high temperature, corals can expel their symbionts in a process termed bleaching, which often is fatal to the coral. Bleaching events have become more common in the past few decades, and have been associated with a number of anthropogenic impacts, including rising sea surface temperatures. However, the causes of the breakdown in the symbiosis are still poorly understood. We hypothesize that a contributing factor is a difference in adaptation temperature between the partners, which would be apparent in differences in temperature-dependence of enzyme kinetics. We are attempting to determine the optimal physiological temperature range of each member of the symbiosis by sequencing and expressing common metabolic enzymes and measuring kinetic parameters (Km, kcat, Arrhenius activation energy), to determine whether enzymes from these taxa have similar functional responses across a physiologically realistic range of temperatures. In addition, we are comparing enzymes from Symbiodinium clades C and D, the latter of which may be more resistant to bleaching than the former. Our initial results indicate that coral (Acropora millepora) and Symbiodinium clade C glyceraldehyde-3-phosphate dehydrogenases (GAPDHs) indeed are adapted to different thermal regimes, with the coral enzyme having greater sensitivity to temperature, evidenced by a higher Arrhenius activation energy and a more rapid increase in Km and kcat as temperature increases.
