Lipids of Indo-Pacific gorgonian corals are modified under the influence of microbial associations

Gorgonian corals form complex interactions with a wide range of microorganisms, which play a key role in maintaining health of the holobiont. To assess the influence that various members of the microbial community exert on the coral lipidome, we analyzed storage (triacylglycerols (TG) and monoalkyldiacylglycerols) and structural (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and lyso-phosphatidylcholine) lipid molecular species. A molecular-genetics analysis showed that colonies of Junceella fragilis were associated with Symbiodinium clade C. Sequences of the parasitic dinoflagellate Blastodinium contortum were found in the gorgonian Dichotella sp. Colonies of Astrogorgia rubra were associated with the filiferan hydroid Hydrichthella epigorgia . Fungal sequences were found in Dichotella sp., A. rubra and Menella sp. A molecular species of ether phospholipids with fungal hydroxylated fatty acids (FA), bacterial odd-numbered FAs and alkyl moiety were detected in gorgonian lipids. As both host coral and some bacteria can synthesize ether lipids, a conclusion was drawn that lipids are likely to be transported from members of the microbial community to the coral host, and some molecular species with an odd-numbered alkyl moiety can be derived from anaerobic bacteria. The TG content of the symbiotic gorgonian J. fragilis was 30-fold higher than in asymbiotic gorgonians. TG 18:3/18:4/18:3 can be considered as a marker of zooxanthellae presence in coral. The hydroid H. epigorgia association did not have any evident contribution to the lipid profile of gorgonian A. rubra . Such markers of soft corals as 24:6n-3 and 24:5n-6 PUFAs were found to be distributed in molecular species of lipids of all the studied corals. A high content of these acids was observed as a characteristic feature in corals of the family Plexauridae ( Menella sp. and A. rubra ). The lipidomic approach allows assessment of the distribution of marker fatty acids in coral lipids, and to tracing the relationships between the microbial community and the coral host.