Lipidomes of phylogenetically different symbiotic dinoflagellates of corals

The structural base of all membranes of symbiotic dinoflagellates (SD) is composed of glycolipids and betaine lipids, whereas triacylglycerols (TG) constitute an energy reserve and are involved in biosynthesis of glycolipids. Since data on the SD lipidome and the host's influence on symbionts' lipidome are scanty, we analyzed and compared the lipidomes of SD isolated from the zoantharian Palythoa tuberculosa and the alcyonarian Sinularia heterospiculata. A sequencing of nuclear gene regions showed that both cnidarians hosted the dinoflagellates Cladocopium sp. (subclades C1 and C3), but the zoantharian also contained the dinoflagellates Durusdinium trenchii (clade D). The presence of the thermotolerant D. trenchii resulted in a higher unsaturation of mono- and digalactosyldiacylglycerols (MGDG and DGDG), but a lower unsaturation of sulfoquinovosyldiacylglycerol (SQDG). The same features were earlier described for same SD from a reef-building coral. Hence, the profile of glycolipid molecules, which form SD thylakoid membranes, seems to be species-specific and does not depend on the host's taxonomic position. In contrast, the betaine lipid molecular species profile of diacylglyceryl-3-O-carboxyhydroxymethylcholine (DGCC), which forms SD cell membranes, can be influenced by the host. The profiles of the TG molecular species from freshly isolated SD have been determined for the first time. These molecular species can be divided on the basis of the acyl group in sn-2 position. The TG with 16:0 acyl group in sn-2 position may enrich total TG of a cnidarian colony and originate from SD cytoplasm. In contrast, TG 18:3/18:4/18:3 may be biosynthetically related with DGDG and concentrated in SD plastoglobules. Our data may be useful for further investigations of natural and technogenic variations in microalgal lipids and symbiont-host interactions in marine ecosystems.