title: Uptake and cellular localization of exogenous lipids by Giardia lamblia, a primitive eukaryote.
abstract: Giardia lamblia trophozoites are unable to carry out de novo lipid synthesis. It is therefore likely that lipids are acquired from the small intestine of the host, in which the trophozoites are exposed to free and conjugated fatty acids, various sterols, phospholipids, bile acids, and bile-lipid mixed micelles. Here we show that G. lamblia is capable of taking up exogenous phosphatidylcholine (PC), phosphatidylinositol (PI), sphingomyelin (SM), cholesterol, ceramide (Cer), and fatty acids. Results from epifluorescence and high-resolution confocal microscopy suggest that fluorescent analogs of SM and PC were accumulated in the plasma membranes, whereas palmitic acid and Cer were localized intracellularly. Interestingly, many of these analogs were also concentrated in perinuclear regions. Similar labeling patterns were observed when the fluorescent analogs were delivered to the parasite via liposomes. To test whether G. lamblia was capable of esterifying exogenous fatty acids into membrane or cellular phospholipids, trophozoites were pulse-labeled with 3H-labeled palmitic or myristic acids and the phospholipids analyzed by thin-layer chromatography. Results document that G. lamblia was able to incorporate exogenous fatty acids into various phospholipids, i.e., PI, PC, PE, and PG. Interestingly, a major portion of radiolabeled fatty acids was incorporated into PG, a phospholipid characteristic of prokaryotic membranes.
authors.affiliation: Department of Biological Sciences, University of Texas, El Paso 79968-0519, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Stevens
authors.forename: G R
authors.initials: GR
authors.lastname: Gibson
authors.forename: R
authors.initials: R
authors.lastname: Adam
authors.forename: J
authors.initials: J
authors.lastname: Maier
authors.forename: M
authors.initials: M
authors.lastname: Allison-Ennis
authors.forename: S
authors.initials: S
authors.lastname: Das
mesh_terms: D000818:Animals; D004951:Esterification; D005057:Eukaryotic Cells / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D005456:Fluorescent Dyes; D005872:Giardia / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D050356:Lipid Metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence
chemical_list: D005227:Fatty Acids; D005456:Fluorescent Dyes