Eicosapentaenoic acid plays a role in stabilizing dynamic membrane structure in the deep-sea piezophile Shewanella violacea: a study employing high-pressure time-resolved fluorescence anisotropy measurement.
Shewanella violacea DSS12 is a psychrophilic piezophile that optimally grows at 30MPa. It contains a substantial amount of eicosapentaenoic acid (EPA) in the membrane. Despite evidence linking increased fatty acid unsaturation and bacterial growth under high pressure, little is known of how the physicochemical properties of the membrane are modulated by unsaturated fatty acids in vivo. By means of the newly developed system performing time-resolved fluorescence anisotropy measurement under high pressure (HP-TRFAM), we demonstrate that the membrane of S. violacea is highly ordered at 0.1MPa and 10°C with the order parameter S of 0.9, and the rotational diffusion coefficient D(w) of 5.4μs(-1) for 1-[4-(trimethylamino)pheny]-6-phenyl-1,3,5-hexatriene in the membrane. Deletion of pfaA encoding the omega-3 polyunsaturated fatty acid synthase caused disorder of the membrane and enhanced the rotational motion of acyl chains, in concert with a 2-fold increase in the palmitoleic acid level. While the wild-type membrane was unperturbed over a wide range of pressures with respect to relatively small effects of pressure on S and D(w), the ΔpfaA membrane was disturbed judging from the degree of increased S and decreased D(w). These results suggest that EPA prevents the membrane from becoming hyperfluid and maintains membrane stability against significant changes in pressure. Our results counter the generally accepted concept that greater fluidity is a membrane characteristic of microorganisms that inhabit cold, high-pressure environments. We suggest that retaining a certain level of membrane physical properties under high pressure is more important than conferring membrane fluidity alone.
Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, Japan.
Keiko
K
Usui
Toshiki
T
Hiraki
Jun
J
Kawamoto
Tatsuo
T
Kurihara
Yuichi
Y
Nogi
Chiaki
C
Kato
Fumiyoshi
F
Abe
D000220:Adaptation, Biological / Q000502:physiology*; D001095:Arachidonic Acids / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D003080:Cold Temperature; D064429:Fatty Acid Synthases / Q000235:genetics / Q000378:metabolism; D005454:Fluorescence Polarization; D017353:Gene Deletion; D008560:Membrane Fluidity / Q000502:physiology*; D012623:Seawater / Q000382:microbiology; D020592:Shewanella / Q000378:metabolism*
D001095:Arachidonic Acids; D064429:Fatty Acid Synthases