Coral reefs are shallow water tropical ecosystems that support marine biodiversity and coastal economies. However, increasing sea temperature, due to climate change, has been pushing corals towards their thermal limit at a speed that corals cannot evolve fast enough to adapt to. Assisted evolution of corals through the manipulation of coral-associated bacteria has been suggested to promote coral survival in a warming ocean as bacteria can share metabolic compounds with their host. One such compound found to enhance bleaching tolerance of corals is mannitol. We aimed to investigate mannitol biosynthesis by bacteria isolated from the coral model, Exaiptasia diaphana. Genomes of 168 isolates were screened for mannitol synthesis genes and ranked by the abundance of essential mannitol synthesis genes. Of these, three isolates belonging to the species Vibrio alginolyticus, Ruegeria scottomollicae, and Brachybacterium sacelli were cultured to quantify mannitol production. Only B. sacelli was found to produce mannitol when a reaction mix of glucose, NAD+, and sodium formate was provided. To understand the production of mannitol by B. sacelli when in symbiosis with E. diaphana, B. sacelli will be co-cultured with E. diaphana, with the two compartments separated by a 0.03 μm membrane. The findings of this study would reveal the potential metabolic roles of B. sacelli in corals, helping the selection of bacterial candidates for assisted evolution interventions.