Jurado A S, Pinheiro T J, Madeira V M
Centro de Biologia Celular, Universidade de Coimbra, Portugal.
Arch Biochem Biophys. 1991 Aug 15;289(1):167-79. doi: 10.1016/0003-9861(91)90457-t.
Bacillus stearothermophilus was grown at the optimal temperature range (center, 65 degrees C), below it (48 and 55 degrees C), and above it (68 degrees C), in a complex medium with or without 2.5 mM Ca2+. The Ca(2+)-supplement improves growth at sub- and supraoptimal temperatures and extends it to higher temperatures (Jurado et al. (1987) J. Gen. Microbiol. 133, 507-513). The phospholipid composition of cultures obtained in the different growth conditions was studied. Phosphatidylethanolamine was always the major phospholipid (40 to 50% of the total phospholipid). Diphosphatidylglycerol, phosphatidylglycerol, a phosphoglycolipid (pgl) and two minor phospholipids (not identified) were also found in the polar lipid extract. The pgl shows a threefold concentration increase as the growth temperature raises from 48 to 68 degrees C. The thermotropic behavior of membrane lipids was studied by differential scanning calorimetry (DSC) and by means of two fluorescent probes of fluidity, 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1,3-di(2-pyrenyl)propane (2Py(3)2Py). The results reveal similar features and clearly show a shift of the temperature range of the phase transition to higher values and an increased structural order of the bilayer, as the growth temperature rises from 55 to 68 degrees C, but an opposite effect was observed from 48 to 55 degrees C. Although the Ca(2+)-supplement to the growth medium has no detectable effect, the addition of Ca2+ to the buffer of liposomes (Ca(2+)-liposomes) has a significant ordering effect at all growth temperatures. These liposomes show a shift of the transition range to higher temperatures and the fluorescent parameters (DPH polarization and intramolecular excimerization of the 2Py(3)2Py) detected an order increase of the probes environment, along and above the main phase transition. Spectra of 31P-NMR and polarized light microscopy clearly show that the lipid extracts exhibit, in all the conditions, typical lamellar phase geometry. We concluded that B. stearothermophilus controls the membrane lipid composition to compensate for the destabilizing effect of high temperatures on the membrane organization or to provide an appropriate packing of phospholipid molecules in a stable bilayer. At high temperatures, Ca(2+)-stimulatory effect on growth is presumably due to a direct Ca2+ interaction with the membrane phospholipids, inducing an increased structural order on the bilayer. The increase of the phase transition temperature in the total lipid extracts as compared with the respective polar lipid fractions probably indicates a stabilizing effect of neutral lipids on membrane bilayers.
嗜热脂肪芽孢杆菌在最佳温度范围（中心温度为65℃）、低于该温度范围（48℃和55℃）以及高于该温度范围（68℃）下，于添加或不添加2.5 mM Ca²⁺的复合培养基中培养。添加Ca²⁺可改善低于和高于最佳温度时的生长情况，并将生长扩展至更高温度（Jurado等人，(1987)《普通微生物学杂志》133, 507 - 513）。研究了在不同生长条件下获得的培养物的磷脂组成。磷脂酰乙醇胺始终是主要的磷脂（占总磷脂的40%至50%）。在极性脂质提取物中还发现了二磷脂酰甘油、磷脂酰甘油、一种磷酸糖脂（pgl）和两种次要磷脂（未鉴定）。随着生长温度从48℃升高到68℃，pgl的浓度增加了三倍。通过差示扫描量热法（DSC）以及两种流动性荧光探针1,6 - 二苯基 - 1,3,5 - 己三烯（DPH）和1,3 - 二（2 - 芘基）丙烷（2Py(3)2Py）研究了膜脂的热致行为。结果显示出相似特征，并清楚地表明，随着生长温度从55℃升高到68℃，相变温度范围向更高值移动，双层结构的有序性增加，但从48℃到55℃观察到相反的效果。尽管向生长培养基中添加Ca²⁺没有可检测到的影响，但向脂质体缓冲液中添加Ca²⁺（Ca²⁺ - 脂质体）在所有生长温度下都有显著的有序化作用。这些脂质体显示出转变范围向更高温度移动，并且荧光参数（DPH极化和2Py(3)2Py的分子内激基缔合物形成）检测到在主要相变及以上温度时探针环境的有序性增加。³¹P - NMR光谱和偏光显微镜清楚地表明，在所有条件下，脂质提取物都呈现出典型的层状相几何结构。我们得出结论，嗜热脂肪芽孢杆菌控制膜脂组成以补偿高温对膜组织的破坏作用，或在稳定的双层中提供磷脂分子的适当堆积。在高温下，Ca²⁺对生长的刺激作用可能是由于Ca²⁺与膜磷脂的直接相互作用，诱导双层结构的有序性增加。与相应的极性脂质部分相比，总脂质提取物中相变温度的升高可能表明中性脂质对膜双层有稳定作用。
