Compounds produced from potential tunicate-blue-green algal symbiosis: A review

Tunicates of the family Didemnidae can be host to two genera of blue-green algae: Synechocystis and Prochloron. The presence of symbiotic algae raises questions as to the exact origin of the biologically important metabolites which have been isolated from tunicates in recent years. Is the compound produced by the tunicate, the alga, or through a combined effort of both organisms? Although this question cannot be fully addressed at the present time, there is evidence which supports the argument that the metabolic origin of certain ascidian metabolites resides in the alga, or is due to a collaborative effort of both organisms. The purpose of this review is to present compounds isolated from tunicates that possess a likely symbiotic relationship with either Synechocystis or Prochloron. Attention will also be given to the ecology of the organisms and the biological activities of metabolites isolated.