title: Electron microscopy may reveal structure of docosahexaenoic acid-rich oil within Schizochytrium sp.
abstract: Schizochytrium sp. is an algae-like microorganism utilized for commercial production of docosahexaenoic acid (DHA)-rich oil and dried microalgae for use as a source of DHA in foods, feeds, and nutritional supplements. Electron microscopic analysis of whole cells of Schizochytrium sp. employing sample preparation by high-pressure freeze substitution suggests the presence of secondary and tertiary semicrystalline structures of triacylglycerols within the oil bodies in Schizochytrium sp. A fine secondary structure consisting of alternating light- and dark-staining bands was observed inside the oil bodies. Dark bands were 29 +/- 1 A in width, and light bands were 22 +/- 1 A in width. The tertiary (three-dimensional) structure may be a multilayered ribbon-like structure which appears coiled and interlaced within the oil body. In freeze-fracture photomicrographs, Schizochytrium oil bodies exhibited fracture planes with terraces averaging 52 +/- 7 A in height which could correspond to the combined width of two halves of two light bands and one dark band observed in the high-pressure freeze substitution photomicrographs. The results suggest that triacylglycerols within Schizochytrium sp. oil bodies may be organized in a triple chain-length structure. High-pressure freeze substitution electron micrographs of two other highly unsaturated oil-producing species of microalgae, Thraustochytrium sp. and Isochrysis galbana, also revealed this fine structure, whereas microalgae containing a higher proportion of saturated oil did not. The results suggest that the staining pattern is not an artifact of preparation and that the triple chain-length conformation of triacylglycerols in Schizochytrium sp. oil bodies may be caused by the unique fatty acid composition of the triacylglycerols.
authors.affiliation: OmegaTech, Inc., Boulder, Colorado 80301-3242, USA. amyashford@omegadha.com
authors.forename: A
authors.initials: A
authors.lastname: Ashford
authors.forename: W R
authors.initials: WR
authors.lastname: Barclay
authors.forename: C A
authors.initials: CA
authors.lastname: Weaver
authors.forename: T H
authors.initials: TH
authors.lastname: Giddings
authors.forename: S
authors.initials: S
authors.lastname: Zeller
mesh_terms: D000818:Animals; D000460:Chlorophyta / Q000737:chemistry / Q000648:ultrastructure; D003593:Cytoplasm / Q000737:chemistry; D004281:Docosahexaenoic Acids / Q000737:chemistry*; D056890:Eukaryota / Q000737:chemistry* / Q000648:ultrastructure*; D005227:Fatty Acids / Q000737:chemistry; D005614:Freeze Fracturing; D017110:Freeze Substitution; D008055:Lipids / Q000032:analysis / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008854:Microscopy, Electron; D010743:Phospholipids / Q000737:chemistry; D014280:Triglycerides / Q000737:chemistry
chemical_list: D005227:Fatty Acids; D008055:Lipids; D010743:Phospholipids; D014280:Triglycerides; D004281:Docosahexaenoic Acids