Studies on Biological and Physical States of Membrane Lipids in the Adaptational Changes of Staphylococcus Aurous

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The bacteria alter their membranes adaptively according to changes of environment and cell structure. We have reported the results that staphylococcal autoplasts synthesized predominantly cardiolipin in their membranes and staphylococcal L-forms synthesized cholesterol newly in addition to an increase of cardiolipin. We have done further study toward clarification of these appearances from the viewpoints of biophysics as well as biochemistry.In order to elucidate why cardiolipin markedly increases in S. aureus cells which lack cell walls, the phase transition characteristics of cardiolipin and phosphatidylglycerol suspensions were investigated by differential scanning calorimetry. The phase transition temperatures for dimyristoylphosphatidylglycerol, tetramyristoylcardiolipin, dipalmitoylphosphatidylglycerol and tetrapalmitoylcardiolipin were 25.0, 47.0, 40.5 and 62.2^ﾟC, respectively. The phase transition temperature for a mixture of two analogous phospholipids was higher than that fo … More r phosphatidylglycerol alone, but lower than that for cardiolipin alone. It increased along with cardiolipin content. The phase transition temperature for cardiolipin was increased in the presence of divalent cations, particularly Ca^<2+>. The results indicate that the head group of cardiolipin by itself can increase the phase transition temperature.Moreover, we checked anti-osmotic stability of liposomes prepared with lipids extracted from normal S. aureus, its L-form and Mycoplasma orale, using the release of carboxyfluorescein trapped in liposomes as an indicator. The trapped carboxyfluorescein was released when the liposomes burst upon the inflow of excess water. Liposomes prepared with the lipids of L-form or Mycoplasma were more resistant to osmotic pressure than those prepared from normal S. aureus. It was found that cardiolipin enhanced the membrane-stability in S. aureus and cholesterol in Mycoplasma.The surface charge of phosphatidylserine liposome and six kinds of bacteria were determined by colloid titration. The amino group was blocked completely by formalin treatment and the negative charge of phosphate and carboxyl group was titrated directly. The amino group can be estimated from the titration difference in the presence and absence of formalin. By this colloid titration method the surface charge can be evaluated stoichrometrically at every pH value, and by formalin treatment the effect of the amino group can be detected quantitatively. Less