Fatty acid and lipid composition of an eicosapentaenoic acid-producing marine bacterium

The major lipids of Shewanella sp. strain SCRC-2738, which produces large amounts of eicosapentaenoic acid (ERA), 20:5(n-3), were phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). These phospholipids comprised the same fatty acid components. The ratio of 20:5 (n-3) to total fatty acids in PG was about threefold greater than in PE. In both phospholipids, 20:5(n-3) was exclusively localized at the sn-2 position. Productivity of 20:5(n-3) was dependent on the growth temperature of the bacterium; it did not vary between 10 and 20°C, but decreased to about 85% at 25°C, declined to half at 27°C, and to below the detection limit at 30°C. Although ¹⁴C-labeled exogenous palmitate, 16:0, oleate, 18:1(n-9), linoleate, 18:2(n-6), and eicosatrienoate, 20:3(n-6) were incorporated into the phospholipids, they were not further metabolized. The desaturation mechanism to 20:5(n-3) of this bacterium seems to be different from those of higher plants in that the lipid-bound fatty acyl chain is used as a substrate for desaturation.