Effects of growth temperature on transport and membrane viscosity in Streptococcus faecalis.

A shift in the growth temperature of Streptococcus faecalis from 37 to 10 degrees C resulted in an 18% increase in the proportion of unsaturated fatty acids. Electron spin resonance spectra of spin-labeled membranes and extracted phospholipids indicated viscosity changes consistent with the alterations in fatty acid composition. Growth temperature had no significant effect on the active transport of leucine and alanine; uptake rates assayed at 10 or 35 degrees C were essentially the same in cells grown at either 10 or 37 degrees C. The relative rapidity of amino acid transport, which presumably contributes to the ability of S. faecalis to thrive in cold environments, is evidently unrelated to adaptive changes in the viscosity of membrane lipids.