LIPIDS AND LIPID-METABOLISM IN THE MICROAEROBIC FREE-LIVING DIPLOMONAD HEXAMITA SP

Hexamita sp. is a free-living heterotrophic flagellate ubiquitous in m icroaerobic environments. It is one of the deepest branching extant eu karyotes, lacking mitochondria and probably an energy-yielding oxidati ve metabolism. Hexamita is cultured in a medium supplemented with foet al calf serum, a ready supply of lipids essential for growth. This stu dy has shown that Heximata does not depend entirely on exogenous lipid supplies and is able to incorporate [1-C-14] acetate, albeit poorly, into its fatty acids, phospholipids and sterols. The major polar lipid s detected were phosphatidylethanolamine, phosphatidylglycerol, phosph atidylcholine, sphingomyelin and cerebrosides. Triacylglycerols were i dentified as the main storage lipids together with sterol esters. The major lipids identified in Hexamita reflect the lipids detected in the culture medium (with the exception of phosphatidylethanolamine); thes e lipids are believed to have been sequestered directly from the cultu re medium. It is possible that phosphatidylethanolamine was synthesise d by Hexamita via phosphotransferase pathways. Incubation with radiola belled palmitate, oleate or stearate showed that no further modificati ons (e.g. desaturation or elongation) had taken place.