STEROLS OF 14 SPECIES OF MARINE DIATOMS (BACILLARIOPHYTA)¹

Abstract

The sterol compositions of 14 species of marine diatoms were determined by gas chromatography and gas chromatography‐mass spectrometry. A variety of sterol profiles were found. The sterols 24‐methylcholesta‐5,22E‐dien‐3β‐ol, cholest‐5‐en‐3β‐ol, and 24‐methylcholesta‐5,24(28)‐dien‐3β‐ol, previously described as the most common sterols found in diatoms, were major sterols in only a few of the species. In light of this and other recent data, it is clear that these three sterols are not typical constituents of many diatom species. Most of the centric species examined had 24‐methylcholesta‐5,24(28)‐dien‐3β‐ol and 24‐methylcholest‐5‐en‐3β‐ol as two of their major sterols. The exception was Rhizosolenia setigera, which possessed cholesta‐5,24‐dien‐3β‐ol as its single major sterol. In contrast to the centric species, the pennate diatoms examined did not have any particular sterols common to most species. Minor levels ofΔ7‐sterols, rarely found in large amounts in diatoms, were found in four species. C29sterols were found in many species; seven contained 24‐ethylcholest‐5‐en‐3β‐ol and three contained 24‐ethylcholesta‐5,22E‐dien‐3β‐ol, reinforcing previous suggestions that C29 sterols are not restricted to higher plants and macroalgae. 24‐Ethylcholesta‐5,22E‐dien‐3β‐ol may prove to be useful for taxonomy of the genus Amphora and the order Thalassiophysales. A major sterol of Fragilaria pinnata was the uncommon algal sterol 23,24‐dimethylcholesta‐5,22E‐dien‐3β‐ol. Cholesta‐5,24‐dien‐3β‐ol was the only sterol found in the culture of Nitzschia closterium. This differed from previous reports of 24‐methylcholesta‐5,22E‐dien‐3β‐ol as the single major sterol in N. closterium. Two C28 sterols possessing an unusual side chain were found in Thalassi‐onema nitzschioides, a C28:2 sterol (16%) and a C28:1 sterol in lower abundance (2.5%), which may be 23‐methylcholesta‐5,22E‐dien‐3β‐ol and 23‐methyl‐5α‐cholest‐22E‐en‐3β‐ol, respectively. The species Cylindrotheca fusiformis, T. nitzschioides, and Skeletonema sp. may be useful as direct sources of cholesterol in mariculture feeds due to their moderate to high content of this sterol.

Influence of climate change on algal community structure and primary productivity of Lake Malawi (East Africa) from the Last Glacial Maximum to present

“…Sterols commonly provide biomarkers for diatoms and dinoflagellates, which are two of the four main algal groups present in Lake Malawi. The dominant sterol(s) in diatoms varies depending on the species present, but brassicasterol (24-methylcholesta-5,22-dien-3b-ol), fucosterol (24-methylcholesta-5,24(28)-dien-3b-ol), and b-sitosterol (24-ethylcholesta-5-en-3b-ol) are common lipids of diatoms (Barrett et al 1995;Volkman et al 1998). The compound dinosterol (4a,23,24-trimethyl-5a-cholest-22-en-3b-ol) is found in many dinoflagellate species (Boon et al 1979;Withers 1983;Pirretti et al 1997) and is commonly used as a biomarker for these organisms (Robison et al 1984;Brassell et al 1987;Volkman et al 1998).…”

Isoprenoid biosynthesis in the diatoms Rhizosolenia setigera (Brightwell) and Haslea ostrearia (Simonsen)

“…For example, the dominant sterol in H. ostrearia is 24-ethylcholest-5-en-3␤-ol (XXI; ref. 34), whereas, in terms of HBIs, H. ostrearia produces C 25 HBI alkenes only, often as mixtures of isomers (XII-XX). These alkenes are regioisomeric with the C 25 HBIs found in R. setigera, with the exception of C 25:5 (VI), which has been identified in both species (23,31).…”

Carbon sources in suspended particles and surface sediments from the Beaufort Sea revealed by molecular lipid biomarkers and compound-specific isotope analysis

“…The 24-methylcholesta-5, 22(E)-dien-3β-ol (C 28 5, 22 , brassicasterol), 24-methylcholesta-5, 24(28)-dien-3β-ol (C 28 5, 24(28) ) and 24-ethylcholest-5-en-3β-ol (sitosterol, C 29 5 ) are common lipids in diatoms (Barrett et al, 1995, Volkman et al, 1998C 28 5, 24(28) and the Z isomer of fucosterol (isofucosterol, 24-ethylcholesta-5, 24(28)(Z)-dien-3β-ol; C 29 5, 24(28) ) are typical of prasinophytes (Volkman et al, 1994). 22 ) is commonly used as a biomarker for dinoflagellates (Robinson et al, 1994a) and 27-nor-24-methylcholesta-5, 22(E)-dien-3β-ol (norC 27 5, 22 ) together with C 28 5, 22 predominate in the marine dinoflagellate Gymnodinium simplex (Goad and Withers, 1982) and in marine invertebrates (Volkman et al, 1981).…”