LIPID COMPOSITION OF CHLORARACHNIOPHYTES (CHLORARACHNIOPHYCEAE) FROM THE GENERA BIGELOWIELLA, GYMNOCHLORA, AND LOTHARELLA¹

Abstract

The Chlorarachniophyceae are unicellular eukaryotic algae characterized by an amoeboid morphology that may be the result of secondary endosymbiosis of a green alga by a nonphotosynthetic amoeba or amoeboflagellate. Whereas much is known about the phylogeny of chlorarachniophytes, little is known about their physiology, particularly that of their lipids. In an initial effort to characterize the lipids of this algal class, four organisms from three genera were examined for their fatty acid and sterol composition. Fatty acids from lipid fractions containing chloroplast-associated glycolipids, storage triglycerides, and cytoplasmic membrane-associated polar lipids were characterized. Glycolipidassociated fatty acids were of limited composition, principally eicosapentaenoic acid [20:5(n-3)] and hexadecanoic acid (16:0). Triglyceride-associated fatty acids, although minor, were found to be similar in composition. The polar lipid fraction was dominated by lipids that did not contain phosphorus and had a more variable fatty acid composition with 16:0 and docosapentaenoic acid [22:5(n-3)] dominant along with a number of minor C 18 and C 20 fatty acids. Crinosterol and one of the epimeric pair poriferasterol/stigmasterol were the sole sterols. Several genes required for synthesis of these sterols were computationally identified in Bigelowiella natans Moestrup. One sterol biosynthesis gene showed the greatest similarity to SMT1 of the green alga, Chlamydomonas reinhardtii. However, homologues to other species, mostly green plant species, were also found. Further, the method used for identification suggested that the sequences were transferred to a genetic compartment other than the likely original location, the nucleomorph nucleus.

Algal lipids, fatty acids and sterols

“…Among macroalgae, cholesterol is the dominant sterol in all the Rhodophyta, fucosterol in Phaeophyta, while the dominant sterol seems to vary within the orders among Chlorophyta (Al Easa et al , 1995) such as isofucosterol in Ulvales and clionasterol in Bryopsidales and Siphonocladales. Among microalgae, Haptophytes are characterized by the presence of unusual dihydroxysterols (pavlovols), pelagophytic algae by 24-propylidenecholesterol, diatoms by 4-desmethyl-23,24-dimethyl steroids, chlororachinophytes by crinosterols, stigmasterols, dinophytes by dinosterols and dinostanols except for the Kareniaceae members and Polarella glacialis (Leblond et al , 2003;Leblond et al , 2005;Leblond et al , 2011;Mooney et al , 2007;Thomson et al , 2004;Volkman et al , 1997). These algal sterols possess benefi cial healthpromoting effects such as hypercholesterolemic, antioxidant, anticancer, antidiabetic, antihypertensive, anti-infl ammatory responses (refer to the review by Kim and Ta, 2011).…”

Betaine lipids in chlorarachniophytes

“…2007); however, their lipid biochemistry is still largely unknown with only two prior papers regarding this topic in existence. In the first paper by Leblond et al . (2005), the major chlorarachniophyte polar lipids, which presumably compose the cytoplasmic membrane, were discovered to generally lack phosphorus, as revealed through a process of spraying thin‐layer chromatography (TLC) plates with a phosphorus‐staining reagent.…”

Sterol Composition and Biosynthetic Genes of the Recently Discovered Photosynthetic Alveolate, Chromera velia (Chromerida), a Close Relative of Apicomplexans

“…Rather, the identified sterols of C. velia have been observed in other, seemingly unrelated classes of photoautotrophic microalgae, such as chlorarachniophytes (Leblond et al. ), glaucocystophytes (Leblond et al. ), and plants as reviewed by Volkman (), thus implying that C. velia shares a sterol biosynthesis pathway(s) ancestral to more than one group of algae.…”