Temperature-induced changes in lipid biomarkers and mycosporine-like amino acids in the psychrophilic dinoflagellate Peridinium aciculiferum

Life at low temperature imposes many constraints linked to sustaining cellular functions. The cold-adapted freshwater dinoflagellate Peridinium aciculiferum has overcome these barriers, often causing blooms in winter but forming resting cysts in spring. Little is known of the biochemical changes that accompany this temperature-induced transformation from vegetative cells to resting cysts. We investigated how the profiles of lipids and mycosporine-like amino acids (MAAs) vary with temperature in vegetative cells and resting cysts of P.aciculiferum. The freshwater dinoflagellate was grown at four temperatures (2.7-7.7 degrees C), simulating the seasonal changes from winter to spring that also induce the transition from cells to cysts. Biochemical profiles were established by liquid chromatography/mass spectrometry with the simultaneous detection of polar and non-polar compounds. Data were analysed by non-metric multidimensional scaling and ANOVA. Over 100 species of galactolipids, betaine lipids, phospholipids and triacylglycerols (TAGs) were found, and many were strong biomarkers for specific temperatures and life stage. Variations in galactolipids, betaine lipids and phospholipids were unidirectional, as shown by an overall decrease in the unsaturation index with temperature. In contrast, changes in TAGs were specific to life stages: short-chain TAGs (cumulative acyl length of 44-52 carbon atoms) decreased in cysts with respect to vegetative cells, while long-chain TAGs (54-62) showed the opposite pattern. The concentration of MAAs decreased with increasing temperature. Final cell yield, a measure of population fitness, also decreased with increasing temperature, confirming the psychrophilic status of P.aciculiferum. We report the first detailed biochemical profiles of vegetative cells and resting cysts for a dinoflagellate and show how small-scale temperature variations alter the biochemical make-up within and between life stages, thus contributing to our understanding of seasonal succession of species.