Structure of membrane lipids and physico-biochemical properties of the plasma membrane from Thermoplasma acidophilum, adapted to growth at 37° C

Abstract

Thermoplasma acidophilum, a mycoplasma-like organism, grows optimally at 56° C and pH 2. The low temperature extreme of growth is 37° C. The plasma membrane of cells grown at 37° C was isolated and characterized physicobiochemically. Membrane lipids which comprise 25% of the membrane dry weight consist mainly of two repetitively methyl-branched C 40 side chains that were ether-linked to two glycerol molecules. The lipid structures were elucidated by combined gas chromatography-mass spectroscopy, direct probe mass spectroscopy and 13C NMR. 37° C-grown cells contained lipids with 42% more pentane cyclization than the 56° C-grown cells. In 37° C-grown cells, phospholipid and serine content decreased by about 10% each, carbohydrate content increased by 5%. EPR studies demonstrated an increase in membrane lipid fluidity of 37° C-grown cells with an upper transition temperature at 35° C which was shifted down by 10° C compared with cells grown at 56° C. Membrane-bound ATPase activities also indicated similar changes upon adaptation. There is a close correlation between membrane fluidity and physiological functioning of this membrane-bound enzyme.