The long and short of it: temperature-dependent modifications of fatty acid chain length and unsaturation in the galactolipid profiles of the diatoms Haslea ostrearia and Phaeodactylum tricornutum

The purpose of this study was to examine the effect of different growth temperatures on the fatty acid compositions of the photosynthetically important galactolipids, mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), of the "blue" pennate diatom, Haslea ostrearia, and the model pennate diatom, Phaeodactylum tricornutum, with the hypothesis that their sn-2 fatty acids would be modulated in the same manner as for dinoflagellates. Positive-ion electrospray ionization/mass spectrometry/mass spectrometry was used to characterize the galactolipids of each diatom. At 20A degrees C, H. ostrearia and P. tricornutum were rich in eicosapentaenoic acid (EPA; C-20:5) at the sn-1 position and in C-16 fatty acids at the sn-2 position of MGDG and DGDG. At 30A degrees C, however, H. ostrearia and P. tricornutum contained no EPA or other C-20 fatty acids, but rather contained higher percentages of C-18 fatty acids at sn-1. At 30A degrees C, no galactolipid in either diatom contained more than three unsaturations on any of its fatty acids. While these two species differ in galactolipid composition, they both possess a similar method of acclimating their galactolipids to a higher growth temperature: reducing the numbers of the longest and shortest fatty acid chains, as well as decreasing the total number of unsaturations.