TIME-RESOLVED POLARIZED FLUORESCENCE STUDIES THE TEMPERATURE ADAPTATION IN BACILLUS-SUBTILIS USING DPH AND TMA-DPH FLUORESCENT-PROBES

The validity of the concept of homeoviscous adaptation was tested for bacteria Bacillus subtilis. The Bacillus subtilis grown at 20 degrees C (referred to as Bs20) exhibit a considerable increase of branched an teiso-C-15, the major fatty acid component of membrane lipids, relativ e to membranes grown at 40 degrees C (Bs40). The time-resolved fluores cence depolarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and -(trim ethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) showed that the se changes in the lipid composition are accompanied by changes in a me an lipid order. In particular, the DPH order parameters (P-2) and (P-4 ) measured in Bs20 membranes at 18 degrees C and in Bs40 membranes at 45 degrees C, respectively, tend to be equal. This effect was less pro nounced for TMA-DPH. Our observations suggest that a physical parallel to the changes of lipid composition is the maintenance of an optimal lipid order in the hydrophobic core of the cytoplasmic membranes. It c an be interpreted as a tendency of Bacillus subtilis to keep the later al pressure in its membranes at an optimal value, independent of the t emperature of cultivation.