Hydrostatic pressure affects membrane and storage lipid compositions of the piezotolerant hydrocarbon-degrading Marinobacter aquaeolei strain #5.

A new piezotolerant alkane-degrading bacterium (Marinobacter hydrocarbonoclasticus strain #5) was isolated from deep (3475 m) Mediterranean seawater and grown at atmospheric pressure (0.1 MPa) and at 35 MPa with hexadecane as sole source of carbon and energy. Modification of the hydrostatic pressure influenced neither the growth rate nor the amount of degraded hexadecane (a 90%) during 13 days of incubation. However, the lipid composition of the cells sharply differed under both pressure condi- tions. At 0.1 MPa, M. hydrocarbonoclasticus #5 bio- synthesized large amounts (a62% of the total cellular lipids) of hexadecane-derived wax esters (WEs), which accumulated in the cells under the form of individual lipid bodies. Intracellular WEs were also synthesized at 35 MPa, but their proportion was half that at 0.1 MPa. This lower WE content at high pressure was balanced by an increase in the total cellular phospholipid content. The chemical composition of WEs formed under both pressure conditions also strongly differed. Saturated Wes were preferentially formed at 0.1 MPa whereas diun- saturated WEs dominated at 35 MPa. This increase of the unsaturation ratio of WEs resembled the one classically observed for bacterial membrane lipid homeostasis. Remarkably, the unsaturation ratio of membrane fatty acids of M. hydrocarbonoclasticus grown at 35 MPa was only slightly higher than at 0.1 MPa. Overall, the results suggest that intracellu- lar WEs and phospholipids play complementary roles in the physiological adaptation of strain #5 to different hydrostatic pressures.