A Survey into Taxonomic and Physiological Differences of Symbiodinium sp., the Photosynthetic Symbiont of Reef-building Corals

Abstract

The dinoflagellate genus Symbiodinium is a popular research topic in the coral reef molecular biology field. Primarily because these organisms serve as the coral holobiont’s primary source of energy, carrying out photosynthesis, and providing hydrocarbons to the coral host. Previous studies have shown the difficulty of isolating Symbiodinium as well as the inherent problems in trying to quantify the diversity of this genus and to qualify the distinct reactions of different Symbiodinium sp. to changing environmental conditions. The main goals of this study are: (1) to detail the relationship between the genetic classification of the organism and its physiology in regard to photosynthesis with a number of established Symbiodinium cultures; and (2) to isolate Symbiodinium from coral of the central Red Sea. To evaluate the photosynthetic physiology of Symbiodinium, a microsensor was used to measure oxygen concentrations along with a phytoplankton analyzer system that used pulse-amplitude-modulation (Phyto-PAM) to measure fluorescence. In order to identify the particular clade that the isolates belonged to, denaturing gradient gel electrophoresis (PCR-DGGE) was used to identify Symbiodinium based on their internal transcribed spacer 2 (ITS2) region. These techniques helped us to achieve our goals in the following ways: Symbiodinium sp. from a culture collection were classified to the subclade level; species-specific and clade-specific photosynthetic profiles were generated; and a Symbiodinium sp. was isolated from the central Red Sea. This study provided preliminary correlation between the photosynthetic difference and Symbiodinium genetic classification; showed the probable existence of a self-protection system inside the Symbiodinium cells by comparing the difference between the initial oxygen production at the beginning of each light step and the oxygen production after light adaptation; and confirmed the possibility of the isolation of Symbiodinium.