Eustigmatophyte microalgae are potential sources of C29 sterols, C22–C28 n-alcohols and C28–C32 n-alkyl diols in freshwater environments

The neutral lipids of three freshwater microalgae from the class Eustigmatophyceae were examined to investigate possible algal sources of lipids in lacustrine sediments. The major neutral lipids in Eustigmatos vischeri (Hulbert) Taylor, Vischeria helvetica (Vischer et Pascher) Taylor and Vischeria punctata Vischer were sterols, long-chain alcohols and alkyl diols. The distributions of long-chain n-alkanols and n-alkenols were very similar in each species, but there were small interspecies differences in the proportions of alkyl diols. Saturated alcohols ranged from 14:0 to 28:0 (both present in trace amounts), with 22:0 as the major alkanol. The latter has previously been reported to be the major n-alcohol in some lacustrine sediments. C16–C30 monounsaturated alcohols were more abundant: 26:1 and 28:1 were the major constituents. The sterol distributions consisted predominantly of 24-ethylcholesterol with small amounts of cholesterol, 24-methylcholesterol, 24-ethylcholesta-5,22E-dien-3β-ol and isofucosterol. These results add to the growing list of microalgae that contain a high proportion of 24-ethylcholesterol, which is more typically associated with higher plants. The long-chain alkyl diols ranged from C28 to C32: the major constituents were the C28 1,13-diol and C30 and C32 1,15 diols which occurred together with smaller amounts of other positional isomers. C30 and C32 alkyl diols have been found in marine eustigmatophytes of the genus Nannochloropsis, and these new results confirm that the same class of compounds occurs in freshwater eustigmatophytes.