MONOMOLECULAR FILM BEHAVIOR OF TETRAETHER LIPIDS FROM A THERMOACIDOPHILIC ARCHAEBACTERIUM AT THE AIR-WATER-INTERFACE

The unusual cyclic bipolar structures of the lipids of thermoacidophilic archaebacteria suggest that they form monolayer membranes. These structures may enhance the ability of these bacteria to live in harsh environments. Monolayer films of conventional lipids have long provided simple models for biomembranes. We have studied the surface properties of monolayer films of two hydrolyzed lipids from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius, as well as several model compounds, at the air/water interface. The archaebacterial lipids studied, glycerol dialkyl nonitol tetraether (GDNT) and glycerol dialkyl glycerol tetraether (GDGT), which are mixtures of closely related molecules, do not form stable monolayer films at temperatures between 16 and 30°C. The dependence of the surface pressure/area and surface potential/area isotherms on the temperature, ionic strength, and pH of the subphase is consistent with the lipids having only one polar head group at the lipid/water interface. There is no evidence to support the existence of a substantial population of “n-shaped” molecules that have both polar head groups at the lipid/water boundary. The hydrocarbon chains dominate the lateral packing of the lipids. However, the sensitivity of GDNT films to subphase pH and ionic strength, compared to the insensitivity of GDGT films, indicates that the nonitol head groups of the GDNT lipids are at the lipid/water interface. © 1990, American Chemical Society. All rights reserved.