Squishy lipids: Temperature effects on the betaine and galactolipid profiles of a C18/C18 peridinin-containing dinoflagellate, Symbiodinium microadriaticum (Dinophyceae), isolated from the mangrove jellyfish, Cassiopea xamachana

Previous work from our laboratory has shown dinoflagellates, which possess the carotenoid peridinin, have been divided into two clusters based on plastid galactolipid fatty acid composition. In one cluster major forms of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), lipids that comprise the majority of photosynthetic membranes, were C-18/C-18 (sn-1/sn-2), with octadecapentaenoic [18:5(n-3)] and octadecatetraenoic [18:4(n-3)] acid as principal fatty acids. The other cluster contained C-20/C-18 major forms, with eicosapentaenoic acid [20:5(n-3)] being the predominant sn-1 fatty acid. In this study, we have found that Symbiodinium microadriaticum isolated from the jellyfish, Cassiopea xamachana, when grown at 30 degrees C, produced MGDG and DGDG with a more saturated fatty acid, 18:4(n-3), at the sn-2 carbon than when grown at 20 degrees C where 18:5(n-3) predominates. This modulation of the sn-2 fatty acid's level of saturation is mechanistically similar to what has been observed in Pyrocystis, a C-20/C-18 dinoflagellate. We have also examined the effect of growth temperature on the betaine lipid, diacylglycerylcarboxyhydroxymethylcholine (DGCC), which has been observed by others to be the predominant non plastidial polar lipid in dinoflagellates. Temperature effects on it were minimal, with very few modulations in fatty acid unsaturation as observed in MGDG and DGDG. Rather, the primary difference seen at the two growth temperatures was the alteration of the amount of minor forms of DGCC, as well as a second betaine lipid, diacylglyceryl-N,N,N-trimethylhomoserine.