The fatty acid and sterol composition of five marine dinoflagellates

The fatty acid and sterol compositions of five species of marine dinoflagel lates (Scrippsiella sp, Symbiodinium microadriaticum Freud, Gymnodinium sp. , Gymnodinium sanguineum Hirasaki and Fragilidium sp.) are reported. All co ntained the major fatty acids that are considered common in dinoflagellates , but the proportions were quite variable, and some species contained low c ontents of some polyunsaturated fatty acids. Concentration ranges for the m ajor fatty acids were: 16:0 (9.0%-24.8%), 18:4(n-3) (2.5%-11.5%), 18:5(n-3) (7.0%-43.1%), 20:5(n-3) (EPA) (1.8%-20.9%), and 22:6(n-3)(DHA) (9.9%-26.3% ). Small amounts of novel very-long-chain highly unsaturated C-28 fatty aci ds occurred in all species. Each dinoflagellate contained a complex mixture of 4-methyl sterols and 4-desmethyl sterols. Four species contained choles terol, although the amounts were highly variable (from 0.2% of total sterol s in Scrippsiella sp. to 45.6% in Fragilidium sp,). All but G. sanguineum c ontained the 4-methyl sterol dinosterol, and, all species contained sterols lacking a double bond in the ring system (i.e. stanols); in Scrippsiella s p. cholestanol composed 24.3% of the total sterols. Other common features o f the 4-methylsterol profiles were the presence of 23,24-dimethyl alkylatio n and unsaturation at Delta(22) in the side chain. In Scrippsiella sp,, fou r steroidal ketones were identified: cholestanone, dinosterone, 4 alpha,23, 24-trimethyl-5 alpha-cholest-8(14)-en-3-one, and dinostanone. The structure s of these corresponded to the major sterols in this species, suggesting th at the sterols and steroidal ketones are biosynthetically linked. Steroidal ketones were not detected in the other species. Although fatty acid profil es can be used to distinguish among algal classes, they were not useful for differentiating among dinoflagellate species. In contrast, whereas some ta xonomic groupings of dinoflagellates display similar sterol patterns, other s, such as the gymnodinoids studied here, clearly do not. The combination o f fatty acid, sterol, and steroidal ketone profiles may be useful complemen tary chemotaxonomic tools for distinguishing morphologically similar specie s. The identification of steroidal ketones supports earlier suggestions tha t certain dinoflagellates might be a significant source of such components in marine environments.