Sterols of morphologically distinct, okadaic acid‐producing Prorocentrum texanum var. texanum and var. cuspidatum isolated from the Gulf of Mexico

Prorocentrum texanum var. texanum and its morphologically distinct yet genetically identical (as based on the sequences of five genes) variety P. texanum var. cuspidatum represent a species of Prorocentrum recently isolated from the Gulf of Mexico. Together, these two varieties represent a sister species to Prorocentrum micans. P. micans has had its sterols, which are ringed lipids common to eukaryotic cell membranes, shown in some studies to be comprised of cholesterol (cholest‐5‐en‐3β‐ol), 23,24‐dimethyl‐cholesta‐5,22‐dien‐3β‐ol, 23,24‐dimethyl‐5α‐cholest‐22E‐en‐3β‐ol, dinosterol, and 4α,23,24‐trimethyl‐5α‐cholestan‐3β‐ol (dinostanol) as major sterols, thus placing it within a previously identified cluster of dinoflagellates characterized by the predominance of cholesterol and dinosterol. In this study we have determined the sterol compositions of these two varieties of P. texanum to be abundant in cholesterol, 23,24‐dimethyl‐cholesta‐5,22‐dien‐3β‐ol, 23,24‐dimethyl‐5α‐cholest‐22E‐en‐3β‐ol, dinosterol, and dinostanol such that the varieties are virtually indistinguishable from each other, making them both in general agreement with the sterols of P. micans, its closest species relative. This expands our knowledge of the sterols of this environmentally important dinoflagellate genus.