Sterol composition of dinoflagellates: Different abundance and composition in heterotrophic species and resting cysts

抄録

The motile cells of the autotrophic dinoflagellates Peridinium umbonatum var. inaequale, Akashiwo sanguinea, Scrippsiella tinctoria, and Prorocentrum micans commonly contain five major sterols: cholesterol, 4-methylcholestan-3-ol, 4,24-dimethylcholestan-3-ol, dinosterol, and dinostanol. The motile cell of the heterotrophic dinoflagellate Protoperidinium crassipes contains cholesterol, 4,24-dimethylcholestan-3-ol, dinosterol, dinostanol, and 4-tetramethylcholestan-3-ol as major free sterols. The dinosterol concentrations of heterotrophic dinoflagellates are about 4-12 times higher than those of autotrophic species, suggesting that the heterotrophic dinoflagellate is an important source of dinosterol in some sediments. 4-Tetramethylcholestan-3-ol has not been reported in cultured samples of other heterotrophic dinoflagellates. The difference in 4-methyl sterol composition in heterotrophic dinoflagellates may be related to the feeds used during the culture experiment. The resting cyst of P. umbonatum var. inaequale contains 4-methylcholestan-3-ol, 4,24-dimethylcholestan-3-ol, dinosterol, dinostanol, and C₃₁Δ^5,22-sterol as major free sterols. The C₃₁Δ^5,22-sterol has not been reported in cultured samples of motile cells from dinoflagellates. This compound might be produced during the resting stage, and thus may serve as a potential biomarker for the resting cysts of dinoflagellates.