Macromolecules Exuded by Symbiotic Dinoflagellates in Culture: Amino Acid and Sugar Composition¹

Five species of symbiotic dinoflagellates in culture exude water‐soluble glycoconjugates. Recovered glycoconjugates of three of the five species were composed of more carbohydrate than protein. The uronic acid content of three algal species that infect scyphistomae of the jellyfish Cassiopeia were higher than those of the two species that do not infect. Analyses of hydrolysates by high‐performance liquid chromatography indicated that the protein components were rich in aspartic acid (asparagine), glutamic acid (glutamine), serine, glycine, leucine, and threonine and contain proline and lysine. Histidine and methionine, when present, were in low concentration. Other sugars detected were glucose and galactose and their respective amines, ribose, mannose, and fucose. Neither sialic acid nor arabinose was detected. The release of glycoconjugates by symbiotic dinoflagellates appears to be a general phenomenon. Some components of these macromolecules could serve as signals that pass between symbionts and hosts, while other components, assuming host digestion, could be a source of previously undetected essential amino acids.