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Title: Mono- and Digalactosyldiacylglycerol Composition of Dinoflagellates. IV. Temperature-Induced Modulation of Fatty Acid Regiochemistry as Observed by Electrospray Ionization/Mass Spectrometry

Author
item LEBLOND, JEFFREY - MTSU
item DAHMEN, JEREMY - MTSU
item Evens, Terence

Submitted to: European Journal of Phycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2009
Publication Date: 11/5/2009
Citation: Leblond, J., Dahmen, J., Evens, T.J. 2009. Mono- and Digalactosyldiacylglycerol Composition of Dinoflagellates. IV. Temperature-Induced Modulation of Fatty Acid Regiochemistry as Observed by Electrospray Ionization/Mass Spectrometry. European Journal of Phycology. 45(1):13-18

Interpretive Summary: With the recently renewed interest in microalgal-based biofuel production, it has become imperative that we gain a fuller understanding of the fundamental physiology of microlalgae. This study examines the effect of temperature on the makeup of the primary lipids of the chloroplast thylakoid membranes in a unique group of dinoflagellates. We observed that, within the temperature range examined that only one of the three primary lipids exhibited a shift in the dominant fatty acid. This response was consistent for all six of the dinoflagellate species/strains examined, and represents a certain lack of plasticity in the thylakoid of this dinoflagellate that is in marked contrast to responses we have observed in green algae. The results presented here indicate that lipid biochemistry in the algae is very complex and will not represent a case of 'one size fits all.'

Technical Abstract: A recent survey of the intact mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively) composition of 35 peridinin-containing dinoflagellates found a division into two clusters, one that possessed C18/C18 (sn-1/sn-2) forms and one that possessed C20/C18 (sn-1/sn-2) forms of MGDG and DGDG. In the C20/C18 cluster, four major forms of MGDG and DGDG were found via positive-ion electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS). Observed as sodiated adducts, these were 20:5/18:5 MGDG, 20:5/18:4 MGDG, 20:5/18:5 DGDG, and 20:5/18:4 DGDG. The discovery of the C20/C18 cluster of dinoflagellates was unexpected because, to our knowledge, there have been no previously reported observations by others of prevalent forms of MGDG and DGDG in peridinin-containing dinoflagellates that deviate from the canonical, commonly observed C18/C18 forms containing octadecapentaenoic [18:5(n-3)] and/or octadecatetraenoic [18:4(n-3)] acid. Because the C20/C18 dinoflagellate forms of MGDG and DGDG are both highly unsaturated and asymmetric in that they always contain 20:5(n-3) at the sn-1 position of glycerol and, depending on the dinoflagellate, either 18:5(n-3) or 18:4(n-3) at the sn-2 position they present a useful model for examining how an environmental condition, namely temperature, affects their composition. Thus, two key questions arise. Firstly, do the fatty acids at the sn-1 and sn-2 positions vary with temperature, and secondly, if so, is the variation species specific? To answer these questions, a strain of Pyrocystis lunula, a peridinin-containing dinoflagellate identified as a C20/C18 cluster organism, was chosen as a model for characterization of MGDG and DGDG at three growth temperatures, 15, 20, and 25° C. In addition, another strain of P. lunula and two strains each of Pyrocystis fusiformis and Pyrocystis noctiluca were chosen for comparison in order to examine the consistency of temperature response in this genus. In this study, we have observed that, within the temperature range examined, two forms of DGDG, but not the forms of MGDG and trigalactosyldiacylglycerol (TGDG), a glycolipid recently identified in dinoflagellates, were the only lipid that displayed a consistent, significant temperature response across all six strains examined. Specifically, the sn-2 fatty acid of DGDG alternated between the 18:5(n-3) and 18:4(n-3) forms in all six strains examined, whereas the sn-1 fatty acid, 20:5(n-3), never varied. The utilization of ESI/MS/MS technology in this study of the genus Pyrocystis has allowed us to present a previously unreported dinoflagellate mechanism of chloroplast lipid modulation in response to temperature.