Lipids of four species of freshwater dinoflagellates

The steroidal derivatives, fatty acid alkyl esters and triacylglycerols have been identified in two cultured dinoflagellates, Woloszynskia coronata and Ceratium furcoides, and natural populations of two species, Peridinium lomnickii and P. cinctum. Within each species, the same sterol moieties occurred in free and esterified forms, but the species differed in the proportion of 4α-methyl and desmethyl sterols. Both groups occurred in the two Peridinium species, whereas W. coronata contained only 4α-methylsterols and C. furcoides, uniquely among dinoflagellates analysed to date, contained only desmethylsterols, although these were analogues of 4α-methylsterols present in the other species. 4α-Methyl steroidal ketones were present in P. lomnickii and W. coronata; cholest-4-en-3-one and 5α-cholestan-3-one were detected in C. furcoides, but no steroidal ketones were detected in P. cinctum. Methyl and ethyl esters of fatty acids (C₁₂C₁₈) were detected in three species, in P. cinctum the ethyl esters were dominant, while phytyl esters occurred only in the Peridinium spp. The molecular composition of triacylglycerols containing only saturated and monoenoic acyl groups was determined by GC-MS. Lower carbon number constituents from W. coronata contained a C₄ acyl group, previously found only in animal milk fats.