PIGMENTS, FATTY ACIDS, AND STEROLS OF THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM1

Abstract

ABSTRACTCultures and field samples of the toxic dinoflagellate Gymnodinium catenatum Graham from Tasmania, Australia, were analyzed for pigment, fatty acid, and sterol composition. Gymnodinium catenatum contained the characteristic pigments of photosynthetic dinoflagellates, including chlorophyll a, chlorophyll c2, and the carotenoids peridinin, dinoxanthin, diadinoxanthin, diatoxanthin, and β,β‐carotene. In midlogarithmic and early stationary phase cultures, the chlorophyll a content ranged 50–72 pg · cell−1, total lipids 956–2084 pg · cell−1, total fatty acids 426–804 pg · cell−1, and total sterols 8–20 pg · cell−1. The major fatty acids (in order of decreasing abundance) were 16:0, 22:6(n‐3), and 20:5(n‐3) (collectively 65–70% of the total fatty acids), followed by 16:1(n‐7), 18:2(n‐6), and 14:0. This distribution is characteristic of most dinoflagellates, except for the low abundance (<3%) of the fatty acid 18:5(n‐3), considered by some authors to be a marker for dinoflagellates. The three major sterols were 4α‐methyl‐5α‐cholest‐7‐en‐3β‐ol, 4α,23,24‐trimethyl‐5α‐cholest‐22E‐en‐3β‐ol (the dinoflagellate sterol, dinosterol), and 4α,23,24‐trimethyl‐5α‐cholest‐7‐en‐3β‐ol. These three sterols comprised about 75% of the total sterols in both logarithmic and early stationary phase cultures, and they were also found in high proportions (22–25%) in natural dinoflagellate bloom samples. 4‐Desmethyl sterols, which are common in most microalgae, were only present in trace amounts in G. catenatum. The chemotaxonomic affinities of G. catenatum and the potential for using specific signature lipids for monitoring toxic dinoflagellate blooms are discussed.