Symbiodiniaceae Cell Cloning from Corals: High Salinity Activates Endogenous Tolerance against the Bleaching Stress

Abstract Coral bleaching is caused by the exocytosis of endosymbiotic dinoflagellates due to overproduction of reactive oxygen species (ROS) in the symbionts when corals are under high temperature and high light stress. Strategies to reduce ROS production and enhance ROS scavenging efficiency in coral symbionts are crucial for preventing the collapse of coral reef ecosystems. However, cell physiology studies of coral symbionts have been hampered by the difficulty of cloning the symbionts. A simple procedure was developed for cloning coral symbionts in this work. Experiments performed with two species of symbionts isolated from Turbinaria sp. revealed that the damages caused by high light at 340 umol photon/m2/s1 was more severe than those caused by high temperature at 36 °C, and high salinity activated endogenous tolerance against the bleaching stress. Pretreatment at 50 ppt salinity reduced the percentage of cells stained for ROS by 59% and 64% in the two species exposed to the bleaching stress compared with those incubated at 30 ppt, and their Fv’/Fm’ recoveries were also improved significantly. These findings suggest that the genomes of coral symbionts have undergone evolutionary processes to develop mechanisms for ameliorating damages caused by high salinity, temperature, and light stress.