The sterol composition of different marine microalgae has been examined to determine the utility of sterols as biomarkers to distinguish members of various algal classes. For example, members of the class Dinophyceae possess certain 4-methyl sterols, such as dinosterol, which are rarely found in other classes of algae. The ability to use sterol biomarkers to distinguish certain dinoflagellates such as the toxic species Karenia brevis Hansen and Moestrup, responsible for red tide events in the Gulf of Mexico, from other species within the same class would be of considerable scientific and economic value. Karenia brevis has been shown by others to possess two major sterols, (24 S )-4 ␣ -methyl-5 ␣ -ergosta-8(14),22-dien-3 ␤ -ol (ED) and its 27-nor derivative (NED), having novel structures not previously known to be present in other dinoflagellates. This prompted the present study of the sterol signatures of more than 40 dinoflagellates. In this survey, sterols with the properties of ED and NED were found in cultures of K. brevis and shown also to be the principal sterols of Karenia mikimotoi Hansen and Moestrup and Karlodinium micrum Larsen, two dinoflagellates closely related to K. brevis . They are also found as minor components of the more complex sterol profiles of other members of the Gymnodinium/Peridinium/Prorocentrum (GPP) taxonomic group. The distribution of these sterols is consistent with the known close relationship between K. brevis , K. mikimotoi , and K. micrum and serves to limit the use of these sterols as lipid biomarkers to a few related species of dinoflagellates. Abbreviations: ED, (24 S )-4 ␣ -methyl-5 ␣ -ergosta-8(14),22dien-3 ␤ -ol; GC/MS, gas chromatography/mass spectrometry; MTBE, methyl-tert -butyl ether; NED, 27-nor-(24 S )-4 ␣ -methyl-5 ␣ -ergosta-8(14),22-dien-3 ␤ -ol; TMS, trimethylsilyl ether

The very long chain highly unsaturated C28 fatty acids, octacosaheptaenoic [28:7(n‐6)] and octacosaoctaenoic acid [28:8(n‐3)], were found to be associated with phospholipids, obtained by fractionation of total lipid extracts into distinct lipid classes, in 4 and 6, respectively, of 16 examined dinoflagellates. An interfraction comparison of fatty acids associated with phospholipids and glycolipids has also shown that the phospholipid fractions contained the majority (over 75% in 12 of 16 strains) of docosahexaenoic acid [22:6(n‐3)] and traces of tetracosanoic acid (24:0). By contrast, the highly unsaturated C18 fatty acids octadecatetraenoic [18:4(n‐3)] and octadecapentaenoic acid [18:5(n‐3)] were primarily recovered from a chloroplast‐associated glycolipid fraction comprised of monogalactosyldiacylglycerol, digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol. In 12 of 16 strains, an interfraction comparison showed that over 90% of 18:5(n‐3) was found to be associated with glycolipids. These findings indicate that the C28 fatty acids are located and probably synthesized in the cytoplasm or in an organelle other than the chloroplast, possibly with 22:6(n‐3) and 24:0 as precursors, whereas the C18 fatty acids 18:4(n‐3) and 18:5(n‐3) are glycolipid constituents apparently synthesized within the chloroplast. The function(s) of these C28 fatty acids as components of phospholipids in cellular membranes is currently unknown.

Two glycolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), are components of chloroplast membranes. This study addresses the lack of information regarding the major intact forms of these glycolipids in photosynthetic dinoflagellates through the use of a full-scan positive-ion electrospray ionization/mass spectrometry (ESI/ MS) survey of MGDG and DGDG in 35 peridinin-containing taxa from the class Dinophyceae. Further analysis using positive-ion electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS) was performed to determine the positional distribution of fatty acids associated with MGDG and DGDG. The dinoflagellates examined were divided into two clusters based on the forms of MGDG and DGDG present. The first possessed 18:5/18:4 MGDG (sn

This study examined the sterol compositions of 102 dinoflagellates using clustering and cluster validation techniques, as a means of determining the relatedness of the organisms. In addition, dinoflagellate sterol-based relationships were compared statistically to 18S rDNA-based phylogenetic relationships using the Mantel test. Our results indicated that the examined dinoflagellates formed six clusters based on sterol composition and that several, but not all, dinoflagellate genera, which formed discrete clusters in the 18S rDNA-based phylogeny, shared similar sterol compositions. This and other correspondences suggest that the sterol compositions of dinoflagellates are explained, to a certain extent, by the evolutionary history of this lineage.

SUMMARY Evolving from the endosymbiosis of a green algal cell by a filose amoeba or amoeboflagellate, the chimearic chlorarachniophytes combine unique features retained from both of their ancestral units. They have preserved from the endosymbiont only the nucleomorph and chloroplast. Four strains from three genera of this algal class were studied to identify a set of non‐phosphorous‐containing polar lipids and their associated fatty acids using the techniques of positive‐ion electrospray ionization/mass spectrometry (ESI/MS) and electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS). Fourteen non‐phosphorous‐containing polar lipids, classified as betaine lipids were primarily identified as forms of diacylglyceryl‐N,N,N‐trimethylhomoserine (DGTS) and its structural isomer diaclyglycerylhydroxymethyl‐N,N,N‐trimethyl‐β‐alanine (DGTA). Though the number of forms of DGTA and DGTA were roughly equal, DGTS composed more of the polar lipid portion present in three of the strains tested, while the fourth, Lotharella globosa, was dominated by forms of DGTA. In addition, a lipid tentatively identified as diacylglycerylcarboxyhydroxymethylcholine (DGCC) was observed twice in minor amounts. The polar lipid‐associated fatty acids of the aforementioned algal strains generally included dodecanoic acid (12:0), tetradecanoic acid (14:0), hexadecanoic acid (16:0), octadecanoic acid (18:0), octadecenoic acid (18:1), and eicosapentaenoic acid [20:5(n‐3)]. The differences in betaine lipid content among the species studied may allow for further conclusions to be drawn regarding the taxonomy of chlorarachniophytes.