The study of the tripartite holobiont in Anthozoans has been integral to understanding coral health and bleaching, driven by disruption of the coral-dinoflagellate symbiosis. While the relationship between corals and their algal symbionts has long been an active area of research, only recently have we come to understand the relationship between dinoflagellates of the family Symbiodiniaceae and their associated bacterial communities. It has been found that these bacterial communities influence growth and calcification, with metabolites they produce positively affecting photophysiology and oxidative stress management. However, these studies have been limited to the analysis of the genera Symbiodinium and Breviolum in their free-living state. Thus, this project aims to examine how the bacterium Labrenzia alexandrii and the natural algal microbiome affect the coral host by enhancing the health of the dinoflagellate host under elevated heat and light conditions while in the symbiotic state. Bacteria of this genus produce indole-3-acetic acid and zeaxanthin, which aid their algal hosts in scavenging reactive oxygen species (ROS) and maintaining photosynthetic efficiency and health. To understand this role within the holobiont, the model organism Exaiptasia diaphana (Aiptasia) will be inoculated with natural, axenic, and L. alexandrii-paired algal cultures, and the resulting benefits will be observed. Synthetic holobionts will be subjected to elevated light and temperature conditions to varying degrees. Subsequently, we will assess the symbiotic response to elevated stressors. Flow cytometry will be used to quantify algal cells, and PAM fluorometry will be used to measure chlorophyll a fluorescence and the maximum quantum yield (Fv/Fm) as indicators of symbiont health. By comparing the bleaching susceptibility of Aiptasia hosting axenic versus bacteria-paired algal symbionts, this research will characterize the extent to which bacteria mitigate coral bleaching by enhancing symbiont health and oxidative stress resistance.

For more information: abhess@eckerd.edu