Lipid and protein composition of membranes of Bacillus megaterium variants in the temperature range 5 to 70°C

Abstract

Membranes were prepared from 4 temperature range variants of B. megaterium: one obligate thermophile, one facultative thermophile, one mesophile, and one facultative psychrophile, covering the temperature interval between 5 and 70°C. The following changes in membrane composition were apparent with increasing growth temperatures: the relative amount of fatty acids increased and that of anteiso acids decreased, the ratio of iso acids to anteiso acids being 0.34 at 5°C and 3.95 at 70°C, and the pair iso/anteiso acids thus seemed to parallel the pair saturated/unsaturated acids in their ability to regulate membrane fluidity; the relative amount of long-chain acids (C16 to C18) increased fivefold over that of short-chain acids (C14 and C15) between 5 and 70°C; the relative amount of phosphatidylethanolamine increased, and this phospholipid accordingly dominated in the thermophilic strains, whereas diphosphatidylglycerol was predominant in the two other strains; and the ratio of micromoles of phospholipid to milligrams of membrane protein increased threefold between 5 and 70°C. Moreover, a quantitative variation in membrane proteins was evident between the different strains. Briefly, membrane phospholipids with higher melting points and packing densities appeared to be synthesized at elevated growth temperatures.