Fatty acid synthesis of an eicosapentaenoic acid-producing bacterium: De novo synthesis, chain elongation, and desaturation systems

The fatty acid synthesis systems of a Shewanella sp., strain SCRC-2738, that produces a large amount of eicosapentaenoic acid were investigated. Two kinds of fatty acid synthesis system, de novo synthesis and chain elongation ones, were detected in the cytosol. The de novo synthesis system required an acyl carrier protein, and produced palmitoyl- and palmitoleoyl-acyl carrier proteins as final products. The chain elongation system also required an acyl carrier protein, and produced an acyl-acyl carrier protein as a product, using palmitoyl-, palmitoleoyl-, stearoyl-, and oleoyl-CoAs as primers but not eicosanoyl- or eicosenoyl-CoA. There were an anaerobic pathway and an aerobic desaturation one for the production of unsaturated fatty acids. Eicosapentaenoic acid seemed to be produced through the aerobic desaturation pathway and not through the anaerobic one, since the latter pathway produced n-7 type monoenoic fatty acids, which are different from eicosapentaenoic acid in the position of the double bond. The desaturase utilized an acyl-acyl carrier protein as a substrate, and this activity increased in the presence of ferredoxin and ferredoxin NADP⁺ reductase. Thus, Shewanella sp., strain SCRC-2738, has novel characteristics as to both fatty acid chain elongation and desaturation systems.