Esterified lipids of the freshwater dinoflagellatePeridinium lomnickii

Steryl esters, phytyl esters and triacylglycerols of a naturally occurring freshwater dinoflagellate,Peridinium lomnickii, were identified using capillary gas chromatography-mass spectrometry (GC-MS). Steryl esters differing in degree of unsaturation were separated, prior to analysis, by argentation thin layer chromatography. 5α(H)-Cholestanol was more dominant, relative to 4α-methylstanols, in steryl esters than in the free sterols, but the same sterol moieties occurred in both fractions. Monoenoic fatty acids were enriched in the steryl esters relative to the free fatty acids. Major acyl groups in steryl esters were 16∶0 or 20∶1, with smaller amounts of 14∶0 and 18∶1. In triacylglycerols the acyl moieties were 14∶0, 16∶0, 18∶1, 16∶1 and 12∶0, in order of decreasing abundance. Phytyl esters, previously inferred to occur in a marine dinoflagellate only by analysis of transesterified products, were identified by GC-MS comparison with authentic compounds. Direct analysis of these esterified lipids has not been reported for freshwater phytoplankton. The 4α-methylstanyl esters, 5α(H)-cholestan-3β-yl esters and phytyl esters occurring inP. lomnickii are further features in common with marine dinoflagellates, additional to the 4α-methylsterols reported previously.