Eicosapentaenoic Acid-Containing Membrane Domain Involved in Cell Division of a Cold-Adapted Bacterium

Abstract

Long-chain omega-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are found in organisms from bacteria to humans as the acyl group of phospholipids in the membrane. Many biophysical studies have been conducted on model membranes and revealed that PUFAs significantly alter the basic properties of lipid bilayers, such as the fluidity, acyl chain order, phase behavior, elastic compressibility, and permeability. However, despite accumulating information on the properties of the PUFA-containing bilayers, information on the physiological role of PUFAs and their molecular mode of action in living cells is very limited. In this study, we demonstrated a novel physiological function of EPA-containing phospholipids in a cold-adapted bacterium, Shewanella livingstonensis Ac10. We previously found that lack of EPA found at the sn-2 position of glycerophospholipids causes a defect in cell division of this strain. To study the localization of EPA-containing phospholipids, we synthesized phospholipid probes labeled with a fluorescent group. A fluorescent probe in which EPA was bound to the glycerol backbone via an ester bond was found to be unsuitable for imaging because EPA was released from the probe by in vivo hydrolysis. To overcome this problem, we synthesized hydrolysis-resistant ether-type phospholipid probes. Using these probes, we found that the fluorescence localized between two nucleoids at the cell center during cell division when the cells were grown in the presence of the eicosapentaenyl group-containing probe, whereas this localization was not observed with the oleyl group-containing control probe. Thus, phospholipids containing an eicosapentaenyl group are specifically enriched at the cell division site. Formation of a membrane microdomain enriched in EPA-containing phospholipids at the nucleoid occlusion site probably facilitates cell division.