OCCURRENCE OF NOVEL C30 STEROLS IN ANTARCTIC SEA-ICE DIATOM COMMUNITIES DURING A SPRING BLOOM

The sterol compositions of natural populations of diatom communities in the sea-ice at McMurdo Sound, Antarctica were determined during the austral spring bloom of 1985, using capillary GC and GC-MS. A range of sterols (C26-C30) were detected in the sea-ice diatom communities; 24-methylenecholesterol, brassicasterol and 24-ethylcholesterol were the major sterols at the Cape Armitage, Erebus, Cape Evans and Wohlschlag Bay sites. The similarity of the sterol profiles to those observed in previous studies of Antarctic freshwater algal communities strongly indicates that diatoms, rather than cyanobacteria or other algal groups previously proposed, are a more probable source of C29 sterols in these extreme environments. Two novel 4-methyl-C30 sterols were also detected: a C30 sterol showing a similar mass spectrum to 4-methyl-24-ethyl-5α-cholest-22-en-3β-ol derived from the prymnesiophyte microalga Pavlova lutheri, but which was chromatographically resolved from this compound; and a stanol presumed to be derived from the C30 sterol. 4-Methyl C30 sterols have not been reported previously in diatoms; their presence, and the occurrence of 4-methyl C28 and C29 sterols, may be due to temperature-induced adaptations in sterol biosynthetic pathways. © 1990.