STEROLS OF 14 SPECIES OF MARINE DIATOMS (BACILLARIOPHYTA)

The sterol compositions of 14 species of marine diatoms were determine d by gas chromatography and gas chromatography-mass spectrometry. A va riety of sterol profiles were found. The sterols 24-methylcholesta-5,2 2E-dien-3 beta-ol, cholest-5-en-3 beta-ol, and 24-methylcholesta-5,24( 28)-dien-3 beta-ol, previously described as the most common sterols fo und in diatoms, were major sterols in only a few of the species. In li ght of this and other recent data, it is clear that these three sterol s are not typical constituents of many diatom species. Most of the cen tric species examined had 24-methylcholesta-5,24(28)-dien-3 beta-ol an d 24-methylcholest-5-en-beta-ol as two of their major sterols. The exc eption was Rhizosolenia setigera, which possessed cholesta-5,24-dien-3 beta-ol as its single major sterol. In contrast to the centric specie s, the pennate diatoms examined did not have any particular sterols co mmon to most species. Minor levels of Delta(7)-sterols, rarely found i n large amounts in diatoms, were found in four species. C-29 sterols w ere found in many species; seven contained 24-ethylcholest-5-en-3 beta -ol and three contained 24-ethylcholesta-5,22E-dien-3 beta-ol, reinfor cing previous suggestions that C-29 sterols are not restricted to high er plants and macroalgae. 24-Ethylcholesta-5,22-E-dien-3 beta-ol may p rove to be useful for taxonomy of the genus Amphora and the order Thal assiophysales. A major sterol of Fragilaria pinnata was the uncommon a lgal sterol 23,24-dimethylcholesta-5,22E-dien-3 beta-ol. Cholesta-5,24 -dien-3 beta-ol was the only sterol found in the culture of Nitzschia closterium. This differed from previous reports of 24-methylcholesta-5 ,22E-dien-3 beta-ol as the single major sterol in N. closterium. Two C -28 sterols possessing an unusual side chain were found in Thalassione ma nitzschioides, a C-28:2 sterol (16%) and a C-28:1 sterol in lower a bundance (2.5%), which may be 23-methylcholesta-5,22E-dien-3 beta-ol a nd 23-methyl-5 alpha-cholest-22E-en-3 beta-ol, respectively. The speci es Cylindrotheca fusiformis, T. nitzschioides, and Skeletonema sp. may be useful as direct sources of cholesterol in mariculture feeds due t o their moderate to high content of this sterol.