title: Lipid composition of multilamellar bodies secreted by Dictyostelium discoideum reveals their amoebal origin.
abstract: When they are fed with bacteria, Dictyostelium discoideum amoebae produce and secrete multilamellar bodies (MLBs), which are composed of membranous material. It has been proposed that MLBs are a waste disposal system that allows D. discoideum to eliminate undigested bacterial remains. However, the real function of MLBs remains unknown. Determination of the biochemical composition of MLBs, especially lipids, represents a way to gain information about the role of these structures. To allow these analyses, a protocol involving various centrifugation procedures has been developed to purify secreted MLBs from amoeba-bacterium cocultures. The purity of the MLB preparation was confirmed by transmission electron microscopy and by immunofluorescence using H36, an antibody that binds to MLBs. The lipid and fatty acid compositions of pure MLBs were then analyzed by high-performance thin-layer chromatography (HPTLC) and gas chromatography (GC), respectively, and compared to those of amoebae as well as bacteria used as a food source. While the bacteria were devoid of phosphatidylcholine (PC) and phosphatidylinositol (PI), these two polar lipid species were major classes of lipids in MLBs and amoebae. Similarly, the fatty acid composition of MLBs and amoebae was characterized by the presence of polyunsaturated fatty acids, while cyclic fatty acids were found only in bacteria. These results strongly suggest that the lipids constituting the MLBs originate from the amoebal metabolism rather than from undigested bacterial membranes. This opens the possibility that MLBs, instead of being a waste disposal system, have unsuspected roles in D. discoideum physiology.
authors.affiliation: Institut de Biologie Intégrative et des Systèmes, Université Laval, Quebec City, Quebec, Canada.
authors.forename: Valérie E
authors.initials: VE
authors.lastname: Paquet
authors.forename: René
authors.initials: R
authors.lastname: Lessire
authors.forename: Frédéric
authors.initials: F
authors.lastname: Domergue
authors.forename: Laetitia
authors.initials: L
authors.lastname: Fouillen
authors.forename: Geneviève
authors.initials: G
authors.lastname: Filion
authors.forename: Ahmadreza
authors.initials: A
authors.lastname: Sedighi
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Charette
mesh_terms: D004023:Dictyostelium / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D005089:Exocytosis; D005227:Fatty Acids / Q000378:metabolism*; D010587:Phagocytosis; D010713:Phosphatidylcholines / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D005227:Fatty Acids; D010713:Phosphatidylcholines; D010716:Phosphatidylinositols