Odd-chain polyunsaturated fatty acids in thraustochytrids

Structure of unusual C21 odd-chain polyunsaturated fatty acids (OC-PUFA), 21:4×7 (4.1%) and 21:5×5 (3.5%), found in thraustochytrid strain TC 04. [Display omitted] ► OC-FA C17–C21were detected in two thraustochytrids isolated from Australian waters. ► The essential PUFA; EPA, AA and DHA accounted for 42–44% of the total FA. ► These OC-PUFA were detected at 21.2–27% of the total FA. ► 19:4ω5, 21:4ω5, 21:5ω5 and 21:4ω7 have not been reported in thraustochytrids. ► We propose a pathway from 17:0 and 19:0 leading to the synthesis of the C21 PUFA. A series of unusual odd-chain fatty acids (OC-FA) were identified in two thraustochytrid strains, TC 01 and TC 04, isolated from waters off the south east coast of Tasmania, Australia. FA compositions were determined by capillary GC and GC–MS, with confirmation of polyunsaturated fatty acids (PUFA) structure performed by analysis of 4,4-dimethyloxazoline derivatives. PUFA constituted 68–74% of the total FA, with the essential PUFA; eicosapentaenoic acid (20:5ω3, EPA), arachidonic acid (20:4ω6, AA) and docosahexaenoic acid (22:6ω3, DHA), accounting for 42–44% of the total FA. High proportions of the saturated OC-FA 15:0 (7.1% in TC 01) and 17:0 (6.2% in TC 04) were detected. The OC-FA 17:1ω8 was present at 2.8% in TC 01. Of particular interest, the C21 PUFA 21:5ω5 and 21:4ω7 were detected at 3.5% and 4.1%, respectively, in TC 04. A proposed biosynthesis pathway for these OC-PUFA is presented. It is possible that the unsaturated OC-PUFA found previously in a number of marine animals were derived from dietary thraustochytrids and they could be useful biomarkers in environmental and food web studies.