Cytotoxic activity of Black Band Disease (BBD) extracts against the symbiotic dinoflagellate Symbiodinium sp

Black band disease (BBD) is an infectious bacterial disease caused by the migration of a black mat of microorganisms across the surface of coral colonies, consuming healthy coral tissue and leaving dead skeleton behind. Although a complex community of bacteria composes the infectious bacterial mat, the most abundant organism present in the mat is a large filamentous, non-heterocyst cyanobacterium, identified as Phormidium corallyticum. In spite of our knowledge on the composition of the BBD mat, the mechanisms by which this disease destroys coral tissue remains unclear. The results presented in this paper show that an extract from the BBD mat has toxic effects on the growth and viability of the symbiotic dinoflagellate Symbiodinium sp. Nonetheless, neither the pellet recovered from the extraction nor extracts from other bacteria have such an effect, suggesting that neither LPS nor membrane proteins are involved in BBD toxicity. Moreover, this compound has a molecular weight lower than 10,000 Da and is heat stable. All these results indicate that there is a toxic compound possibly involved in the mechanism of pathogenesis of BBD in corals. Further studies will involve the isolation and characterization of such compound. K e y w o r d s coral, black band disease, toxin,