Sterols of Testudodinium testudo (formerly Amphidinium testudo): Production of the Δ8 (14) sterol gymnodinosterol and chemotaxonomic relationship to the Kareniaceae.

Testudodinium testudo is a peridinin-containing dinoflagellate recently renamed from Amphidinium testudo. While T. testudo has been shown via phylogenetic analysis of small subunit ribosomal RNA genes to reside in a clade separate from the genus Amphidinium, it does possess morphological features similar to Amphidinium sensu stricto. Previous studies of Amphidinium carterae and Amphidinium corpulentum have found the sterols to be enriched in Δ8(14) sterols, such as 4α-methyl-5α-ergosta-8(14),24(28)-dien-3ß-ol (amphisterol), uncommon to most other dinoflagellate taxa and thus considered possible biomarkers for the genus Amphidinium. Here, we provide an examination of the sterols of T. testudo and show they are dominated not by amphisterol, but rather by a different Δ8(14) sterol, (24R)-4α-methyl-5α-ergosta-8(14),22-dien-3ß-ol (gymnodinosterol), previously thought to be a major sterol only within the Kareniaceae genera Karenia, Karlodinium, and Takayama. Also found to be present at low levels were 4α-methyl-5α-ergosta-8,14,22-trien-3ß-ol, a sterol previously observed in Karenia brevis to be an intermediate in the production of gymnodinosterol, and cholesterol, a sterol common to many other dinoflagellates. The presence of gymnodinosterol in T. testudo is the first report of this sterol as the sole major sterol in a dinoflagellate outside of the Kareniaceae. The implication of this chemotaxonomic relationship to the Kareniaceae is discussed.

Sterols of Amphidinium species in the Operculatum Clade: Predominance of cholesterol instead of Δ8 (14) sterols previously considered Amphidinium-specific biomarkers.

The dinoflagellates Amphidinium carterae and Amphidinium corpulentum have been previously characterized as having Δ8(14) -nuclear unsaturated 4α-methyl-5α-cholest-8(14)-en-3ß-ol (C28:1 ) and 4α-methyl-5α-ergosta-8(14),24(28)-dien-3ß-ol (amphisterol; C29:2 ) as predominant sterols, where they comprise approximately 80% of the total sterol composition. These two sterols have hence been considered as possible major sterol biomarkers for the genus. Here, we have examined the sterols of four recently identified species of Amphidinium (Amphidinium fijiense, Amphidinium magnum, Amphidinium theodori, and Amphidinium tomasii) that are closely related to Amphidinium operculatum as part of what is termed the Operculatum Clade to show that each species has its sterol composition dominated by the common dinoflagellate sterol cholesterol (cholest-5-en-3ß-ol; C27:1 ), which is found in many other dinoflagellate genera, rather than Δ8(14) sterols. While the Δ8(14) sterols 4α-methyl-5α-cholest-8(14)-en-3ß-ol and 4α,23,24-trimethyl-5α-cholest-8(14),22E-dien-3ß-ol (C30:2 ) were present as minor sterols along with another common dinoflagellate sterol, 4α,23,24-trimethyl-5α-cholest-22E-en-3ß-ol (dinosterol; C30:1 ), in some of these four species, amphisterol was not conclusively observed. From a chemotaxonomic perspective, while this does reinforce the genus Amphidinium's ability to produce Δ8(14) sterols, albeit here as minor sterols, these results demonstrate that caution should be used when considering Δ8(14) sterols, especially amphisterol, as Amphidinium-specific biomarkers within these species where cholesterol is the predominant sterol.

First examination of sterols in the marine dinoflagellate genus Vulcanodinium.

Vulcanodinium is an ecologically relevant dinoflagellate genus due to its production of neurotoxins known as pinnatoxins. We present here the first examination of the sterols of a Vulcanodinium rugosum isolate. Sterols are ringed lipids that assist in maintaining rigidity of cellular membranes, and the Dinophyceae are well-studied for their ability to produce a diverse array of sterols, many of which have chemotaxonomic utility. We have determined that V. rugosum produces a set of major sterols, namely cholesterol, dinosterol, 4α,24-dimethyl-5α-cholest-22E-en-3ß-ol, and 4α,24-dimethyl-5α-cholestan-3ß-ol, common to the Dinophyceae. However, this displayed marked differences from those studied members of the genera Scrippsiella and Peridinium, the closest phylogenetic relatives. Included in these differences is production by V. rugosum of a much lower percentage of dinostanol, a saturated form of dinosterol.