Fatty Acid Metabolism in Bacteria That Produce Eicosapentaenoic Acid Isolated from Sea Urchin Strongylocentrotus nudus

The biosynthetic pathway of 5Z, 8Z, 11 Z, 14Z, 18Z-eicosapentaenoic acid (EPA, C20: 5 n-3) in Vibrio sp. isolated from sea urchin was studied. EPA was one of the major fatty acid constituents (17.5%) in the bacteria, while the other polyunsaturated fatty acids were trace elements (<1.0%). The radioactivity in the fatty acids was measured by a liquid scintillation counter after separating with argentic impregnated thin layer chromatography. The conversion from [1-¹⁴C]C18: ln-9 to C20: 5n-3 was oxygen-dependent and cerulenin-sensitive. In the presence of cerulenin, the accumulation of radioactive trienoic fatty acid increased and tetra- and pentaenoic acids decreased. These results suggest that C18: ln-9 was aerobically desaturated and elongated to C20: 5n-3 via C18: 3. Since [1-¹⁴C] C20 : 4n-6 and [1-¹⁴C] C18 : 3n-3 were converted to C20 : 5n-3, the desaturation of n-6 to n-3 unsaturated fatty acids occur in both Cl8 and C20 chain length.