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Title: LIPID COMPOSITION OF CHLORARACHNIOPHYTES (CHLORARACHNIOPHYCEAE) FROM THE GENERA BIGELOWIELLA, GYMNOCHLORA, AND LOTHARELLA

Author
item LEBLOND, JEFFREY - MTSU
item DAHMEN, JEREMY - MTSU
item SEIPELT, REBECCA - MTSU
item ELROD-ERICKSON, MATTHEW - MTSU
item CAHOON, BRUCE - MTSU
item KINCAID, RODNEY - MTSU
item Evens, Terence
item CHAPMAN, PETER - US EPA

Submitted to: Journal of Phycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2004
Publication Date: 4/1/2005
Citation: Leblond, J., Dahmen, J., Seipelt, R., Elrod-Erickson, M., Cahoon, B., Kincaid, R., Evens, T.J., Chapman, P. 2005. Lipid composition of chlorarachniophytes (chlorarachniophyceae) from the genera bigelowiella, gymnochlora, and lotharella. J Phycol, v.41. issue 2. p.311-321

Interpretive Summary: The algal class Chlorarachniophyceae is comprised of a small group of unicellular eukaryotic algae that are often characterized by an unusual amoeboid morphology. This morphology is hypothesized to be the result of a secondary endosymbiosis in which a green alga was engulfed as prey by a nonphotosynthetic amoeba or amoebaflagellate. Whereas much is known about the phylogenetic relationships of individual chlorarachniophytes to one another, and to possible ancestral host amoebaflagellates, little is known about their physiology, particularly that of their lipids. In an initial effort to characterize the lipids of this algal class, five organisms were examined for their fatty acid and sterol composition. Results indicate that these algae produce two sterols, which is indicative of a green algal ancestor. However, the fatty acid profile is unlike any known profile of the green algal genera Chlorella, which brings into question the hypothesis that Chlorella may be the origin of the chloroplast.

Technical Abstract: The algal class Chlorarachniophyceae is comprised of a small group of unicellular eukaryotic algae that are often characterized by an unusual amoeboid morphology. This morphology is hypothesized to be the result of a secondary endosymbiosis in which a green alga was engulfed as prey by a nonphotosynthetic amoeba or amoebaflagellate. Whereas much is known about the phylogenetic relationships of individual chlorarachniophytes to one another, and to possible ancestral host amoebaflagellates in the genera Cercomonas and Heteromita, little is known about their physiology, particularly that of their lipids. In an initial effort to characterize the lipids of this algal class, five organisms were examined for their fatty acid and sterol composition. These included Bigelowiella natans, Gymnochlora stellata, Lotharella amoeboformis, and a Lotharella sp. Fatty acids from lipid fractions containing chloroplast-associated glycolipids, cytoplasmic membrane-associated phospholipids, and storage triglycerides were characterized. Glycolipid-associated fatty acids were found to be derived from the common algal/plant lipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), and were found to be of limited composition, containing principally eicosapentaenoic acid [20:5(n-3)] and hexadecanoic acid (16:0). These two fatty acids ranged, on an intrafraction basis, in relative percentages from 67-90% and 10-29%, respectively. Triglyceride-associated fatty acids, although minor, were found to be similar in composition in some respects to glycolipid-derived fatty acids. Phospholipid-associated fatty acid composition was more variable. The principal phospholipid fatty acids, 16:0 (25-32%) and docosapentaenoic acid [22:5(n-3)] (26-35%), were found along with a number of minor C18 and C20 fatty acids. All organisms contained only two sterols as free sterols. These were identified as 24-ethylcholesta-5,22E-dien-3'-ol (70-95%) and 24-methylcholesta-5,22E-dien-3 ' -ol (5-30%). Several genes encoding activities required for synthesis of these sterols were computationally identified in B. natans. The sterol biosynthesis gene within this metabolic pathway with the greatest similarity, by far, was SMT1 of the green alga, Chlamydomonas reinhardtii. However, homologues related to other species, mostly green plant species, were also found. Further, the method of identification suggested that the sequences have been transferred to a genetic compartment other than the likely original location, the nucleomorph nucleus.