Eustigmatophyte microalgae are potential sources of C-29 sterols, C-22-C-28 n-alcohols and C-28-C-32 n-alkyl diols in freshwater environments

The neutral lipids of three freshwater microalgae from the class Eustigmato phyceae were examined to investigate possible algal sources of lipids in la custrine sediments. The major neutral lipids in Eustigmatos vischeri (Hulbe rt) Taylor, Vischeria helvetica (Vischer et Pascher) Taylor and Vischeria p unctata Vischer were sterols, long-chain alcohols and alkyl diols. The dist ributions 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 i n 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. C-16 -C-30 monounsaturated alcohols were more abundant: 26:1 and 28:1 were the m ajor constituents. The sterol distributions consisted predominantly of 24-e thylcholesterol with small amounts of cholesterol, 24-methylcholesterol, 24 -ethylcholesta-5,22E-dien-3 beta-ol and isofucosterol. These results add to the growing list of microalgae that contain a high proportion of 24-ethylc holesterol, which is more typically associated with higher plants. The long -chain alkyl diols ranged from C-28 to C-32: the major constituents were th e C-28 1,13-diol and C-30 and C-32 1,15 diols which occurred together with smaller amounts of other positional isomers. C-30 and C-32 alkyl diols have been found in marine eustigmatophytes of the genus Nannochloropsis and the se new results confirm that the same class of compounds occurs in freshwate r eustigmatophytes. (C) 1999 Elsevier Science Ltd. All rights reserved.