第32回極域生物シンポジウムポスター発

堀 竜二

奥山 英登志

渡邉 研太郎

西田 孝伸

National Institute of Polar Research Repository

細菌の低温適応と細胞の疎水度  堀竜二 1、西田孝伸 1、渡邉研太郎 2、奥山英登志 1 1北海道大学・大学院環境科学院 2国立極地研究所  Cold-adaptation of bacteria and their cell surface hydrophobicity  Ryuji Hori1, Takanori Nishida1, Kentaro Watanabe2, and Hidetoshi Okuyama1  1Graduate School of Environmental Science, Hokkaido University 2National Institute of Polar Research  Long-chain polyunsaturated fatty acids (LCPUFAs) such as eicosapentaenoic acid (EPA) are considered to have an antioxidative function in psychrophilic and psychrotrophic bacterial cells, which is based on their cell membrane-shielding effect. The membrane-shielding effect is defined as a structural function of cell membrane phospholipids acylated in combination with a LCPUFA and a medium chain saturated or monounsaturated fatty acid, by which a more hydrophobic interface of alkyl chains can be formed between the phospholipid bilayer, and this hydrophobic structure has potential to hinder the entry of hydrophilic compounds such as reactive oxygen species including hydrogen peroxide (H2O2). Using an EPA-producing bacteriium Shewanella marinitestina IK-1 (IK-1) and its EPA-deficient mutant (IK-1Δ8), which were grown at 20 ºC, the cell membrane-shielding effect of EPA against H2O2 and tert-butyl hydroperoxide, an analog of H2O2, was confirmed. Interestingly, IK-1 was more resistant even against various hydrophilic antibiotics (ampicillin sodium, kanamycin sulfate and streptomycin sulfate) than IK-1Δ8. Analysis of the cell hydrophobicity of these strains by the bacterial adhesion to hydrocarbon method demonstrated that IK-1 was more hydrophobic than IK-1Δ8. Considering that the content of EPA was approximately 10% of total fatty acids of IK-1 cells grown at 20 ºC and that lower growth temperature led to higher contents of EPA in IK-1, it is suggested that EPA contributed to the cell surface hydrophobicity and to the adaptability to low temperature. On the other hand, IK-1 was more susceptible to a hydrophobic oxidative phosphorylation uncoupler, carbonyl cyanide m-chloro phenyl hydrazone (CCCP) than IK-1Δ8. CCCP could be accumulated in cells of IK-1 more effectively than those of IK-1Δ8. Taken together, it is suggested that the higher cell hydrophobicity of LCPUFA-possessing bacteria could facilitate their growth at low temperature by controlling the uptake of environmental hydrophilic and hydrophobic compounds.        Figure 1: The membrane-shielding effects of long-chain polyunsaturated fatty acids. The hydrophobic layer (shown by two parallel broken lines) composed only of saturated chains (red) between outer and inner leaflets of the membrane may act as the shield of hydrophilic compounds such as H2O2. LCPUFA is in blue. The flow of H2O2 is illustrated by two types of arrow (Cited from ref. 1) with permission).     Acknowledgements The authors appreciate Drs. Y. Yano of National Research Institute of Fisheries Science and N. Morita of National Institute of Advanced Industrial Science and Technology (AIST) for providing S. marinintestina IK-1 and its mutant IK-1Δ8, respectively.    References 1) H. Okuyama, Y. Orikasa, and T. Nishida (2008) Significance of antioxidative functions of eicosapentaenoic and docosahexaenoic acids in marine Microorganisms. Appl. Environ. Microbiol. 74: 570–574. 2) T. Nishida, R. Hori, and N. Morita (2010) Membrane eicopentaenoic acid is involved in the hydrophobicity of bacterial cells and affects the entry of hydrophobicity of bacterial cells and affects the entry of hydrophilic and hydrophobic compounds. FEMS Microbiol. Lett. 306: 91–96. Figure 2. Effects of the concentration of H2O2 and CCCP on the growth of S marinintestina IK-1 and its EPA-deficient mutant IK-1Δ8. IK-1 was more resistant to H2O2 than IK-18, whereas the former was less resistant to CCCP than the latter. The surface hydrophobicity was greater in IK-1 cells (94% ± 1%) than in IK-18 cells (99% ± 1%).  (Cited from ref. 2) with permission). 

Cold-adaptation of bacteria and their cell surface hydrophobicity

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Cold-adaptation of bacteria and their cell surface hydrophobicity

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