Energy transduction and transport processes in thermophilic bacteria

Bacterial growth at the extremes of temperature has remained a fascinating aspect in the study of membrane function and structure. The stability of the integral membrane proteins of thermophiles make them particularly amenable to study. Respiratory enzymes of thermophiles appear to be functionally similar to the mesophilic enzymes but differ in their thermostability and unusual high turnover rates. Energy coupling at extreme temperatures seems inefficient as suggested by the high maintenance oefficients and the high permeability ofthe cell membrane to protons. Nevertheless, membranes maintain their structure at these extremes through changes in fatty acid acyl chain composition. Archaebacteria synthesize novel membrane-span-ning lipids with unique physical characteristics. Thermophiles have adapted to life at extreme temperatures byusing sodium ions rather than protons as coupling ions in solute transport. Genetic and biochemical studies of these systems now reveal fundamental principles of such adaptations. The recent development of reconstitution techniques using membrane-spanning lipids allows a rigorous biochemical characterization f membrane proteins of extreme ther-mophiles in their natural environment. KEY WORDS: Thermophiles; archaebacteriae; extremophiles; olute transport; energy transduction; reconstitution; membrane fusion; tetraether lipids