Membrane fluidity inBacillus subtilis. Validity of homeoviscous adaptation

The validity of the principle of homeoviscous adaptation forBacillus subtilis was tested by comparing fluorescence aniaotropy (1,6-diphenyl-1,3,5-hexatriene) and electron-spin resonance (16-doxylstearate) measurements carried out in isolated plasma membranes and in phospholipid fractions. The physical measurements were supplemented by fatty-acid analysis. The results support our previous findings on intact cells. The thermoadaptive mechanism ofB. subtilis manifested as an increase in relative proportion of branchedanteiso-C15 andanteiso-C17 fatty acids, are not strong enough to compensate for the marked physical change of membrane fluidity induced by temperature decrease.