Role of endosymbiotic zooxanthellae and coral mucus in the adhesion of thecoral-bleaching pathogen Vibrio shiloi to its host

Vibrio shiloi. the causative agent of bleaching the coral Oculina patagonic a in the Mediterranean Sea, adheres to its coral host by a beta-(D)-galacto pyranoside-containing receptor on the coral surface. The receptor is presen t in the coral mucus, since V. shiloi adhered avidly to mucus-coa ted ELISA plates. Adhesion was inhibited by methyl-beta -D-galactopyranoside. Remova l of the mucus from O. patagonica resulted in a delay in adhesion of V shil oi to the coral, corresponding to regeneration of the mucus. DCMU inhibited the recovery of adhesion of the bacteria to the mucus-depleted corals, ind icating that active photosynthesis by the endosymbiotic zooxanthellae was n ecessary for the synthesis or secretion of the receptor. Further evidence o f the role of the zooxanthellae in producing the receptor came from a study of adhesion of V. shiloi to different species of corals. The bacteria fail ed to adhere to bleached corals and white (azooxanthellate) O. patagonica c ave corals, both of which lacked the algae. In addition. V. shiloi adhered to two Mediterranean corals (Phyllangia and Cladocora) that contained zooxa nthellae and did not adhere to two azooxanthellate Mediterranean corals (Ph yllangia and Polycyathus). V. shiloi demonstrated positive chemotaxis towar ds the mucus of O. patagonica. The data demonstrate that endosymbiotic zoox anthellae contribute to the production of coral mucus and that V. shiloi in fects only mucus-containing, zooxanthellate corals. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.