特集　ここまで明らかになったω3脂肪酸 「細菌におけるω3長鎖高度不飽和脂肪酸の生合成と生理機能」

抄録

Bacteria that belong to Shewanella, Moritella, Colwellia, Photobacterium, and other genera synthesize 3 long-chain polyunsaturated fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid de novo. The bacterial enzymes for the synthesis of these fatty acids share sequence similarity with polyketide synthases. Their synthesis proceeds in an oxygen molecule-independent manner, implying that the double bonds are introduced by dehydratase, not by desaturase. Comparison of phenotypes of EPA-producing bacteria with their EPA-deficient mutant revealed various physiological functions of EPA. In Shewanella livingstonensis Ac10 and Shewanella violacea DSS12, EPA is required for their normal cell division at low temperatures and high pressures, respectively. In these bacteria, EPA depletion does not cause an apparent decrease of bulk membrane fluidity, suggesting that EPA plays a specific physiological role other than increasing membrane fluidity. A fluorescent analog of EPA-containing phospholipids was shown to accumulate at the cell division site of S. livingstonensis Ac10, suggesting that EPA-containing phospholipids play an assistant beneficial role in cell division at the division site through their accumulation at the site. In Shewanella marinintestina IK-1, EPA depletion increases sensitivity to hydrophilic growth inhibitors such as hydrogen peroxide and resistance to hydrophobic compounds, suggesting a membrane-shielding function of EPA. Recent studies indicate that EPA is also involved in the biogenesis of membrane proteins and extracellular membrane vesicles.