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J. Bacteriol. doi:10.1128/JB.00881-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Eicosapentaenoic acid plays a beneficial role in membrane organization and cell division of a cold-adapted bacterium, Shewanella livingstonensis Ac10

Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan; Ibaraki Prefectural University of Health Sciences, Inashiki, Ibaraki 300-0394, Japan; and Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

^* To whom correspondence should be addressed. Email: kurihara{at}scl.kyoto-u.ac.jp. esakin{at}scl.kyoto-u.ac.jp.

	Abstract

Shewanella livingstonensis Ac10, a psychrotrophic Gram-negative bacterium isolated from Antarctic seawater, produces eicosapentaenoic acid (EPA) as a component of phospholipids at low temperatures. EPA constitutes about 5% of the total fatty acids of the cells grown at 4°C. We found that five genes, termed orf2, orf5, orf6, orf7, and orf8, are specifically required for the synthesis of EPA by targeted disruption of the respective genes. The mutants lacking EPA showed significant growth retardation at 4°C but not at 18°C. Supplementation of a synthetic phosphatidylethanolamine that contained EPA at the sn-2 position complemented the growth defect. The EPA-less mutant became filamentous, and multiple nucleoids were observed in a single cell at 4°C, indicating that the mutant has a defect in cell division. Electron microscopy of the cells by high-pressure freezing and freeze substitution revealed abnormal intracellular membranes in the EPA-less mutant at 4°C. We also found that the amounts of several membrane proteins were affected by the depletion of EPA. While polyunsaturated fatty acids are often regarded to increase the fluidity of the hydrophobic membrane core, diffusion of a small hydrophobic molecule, pyrene, in the cell membranes and large unilamellar vesicles prepared from the lipid extracts was very similar between the EPA-less mutant and the parent strain. These results suggest that EPA in S. livingstonensis Ac10 is not required for bulk bilayer fluidity but plays a beneficial role in membrane organization and cell division at low temperatures possibly through specific interaction between EPA and proteins involved in these cellular processes.