Membrane eicosapentaenoic acid is involved in the hydrophobicity of bacterial cells and affects the entry of hydrophilic and hydrophobic compounds

Eicosapentaenoic acid (EPA)‐producing Shewanella marinintestina IK‐1 (IK‐1) and its EPA‐deficient mutant IK‐1Δ8 (IK‐1Δ8) were grown on microtitre plates at 20 °C in a nutrient medium that contained various types of growth inhibitors. The minimal inhibitory concentrations of hydrogen peroxide and tert ‐butyl hydroxyl peroxide were 100 μM and 1 mM, respectively, for IK‐1 and 10 and 100 μM, respectively, for IK‐1Δ8. IK‐1 was much more resistant than IK‐1Δ8 to the four water‐soluble antibiotics (ampicillin sodium, kanamycin sulphate, streptomycin sulphate, and tetracycline hydrochloride) tested. In contrast, IK‐1 was less resistant than IK‐1Δ8 to two hydrophobic uncouplers: carbonyl cyanide m ‐chloro phenylhydrazone (CCCP) and N,N ′‐dicyclohexylcarbodiimide (DCCD). The hydrophobicity of the IK‐1 and IK‐1Δ8 cells grown at 20 °C was determined using the bacterial adhesion to hydrocarbon method. EPA‐containing (∼10% of total fatty acids) IK‐1 cells were more hydrophobic than their counterparts with no EPA. These results suggest that the high hydrophobicity of IK‐1 cells can be attributed to the presence of membrane EPA, which shields the entry of hydrophilic membrane‐diffusible compounds, and that hydrophobic compounds such as CCCP and DCCD diffuse more effectively in the membranes of IK‐1, where they can fulfil their inhibitory activities, than in the membranes of IK‐1Δ8.