Membrane fluidity and chemotaxis: Effects of temperature and membrane lipid composition on the swimming behavior of <em>Salmonella typhimurium</em> and <em>Escherichia coli</em>

The effect of membrane fluidity on the tumbling frequency, velocity, attractant response times, and viability was studied in strains of Salmonella typhimurium and Escherichia coli. Lipid composition was altered (1) by varying the growth temperature, (2) by using the unsaturated fatty acid auxotroph of E. coli 30E, or (3) by growing S. typhimurium in the presence of the unsaturated fatty acid synthesis inhibitor 3-decynoyl-N-acetyl-cysteamine supplemented with elaidic or oleic acids. Velocity increased linearly with increasing observation temperature and was independent of growth temperature. Tumble frequency showed a bell-shaped dependence on temperature with the highest tumble frequency near the growth temperature. No significant differences in tumble frequency or response times were observed between cells grown on oleic or elaidic acid above or below the elaidic acid transition temperature of 30°C. E. coli strain 30E, when grown on elaidic acid, however, shows a distinct loss of viability when incubated below 30°C, which can explain the previously reported lack of chemotaxis in such cells. A three-component model including a tumble regulator as a control in chemotaxis is capable of explaining the results. Some membrane processes are critically dependent on membrane fluidity and others are not.

研究了膜流动性对鼠伤寒沙门氏菌和大肠杆菌菌株的翻滚频率、速度、趋化剂响应时间和生存能力的影响。通过以下方式改变脂质组成：（1）改变生长温度；（2）使用大肠杆菌30E的不饱和脂肪酸营养缺陷型；（3）在不饱和脂肪酸合成抑制剂3 - 癸炔酰 - N - 乙酰基 - 半胱胺存在的情况下，添加反油酸或油酸培养鼠伤寒沙门氏菌。速度随观察温度的升高呈线性增加，且与生长温度无关。翻滚频率对温度呈钟形依赖关系，在生长温度附近翻滚频率最高。在高于或低于30°C的反油酸转变温度下，在油酸或反油酸上生长的细胞之间，翻滚频率或响应时间没有显著差异。然而，大肠杆菌30E菌株在反油酸上生长时，在低于30°C孵育时表现出明显的生存能力丧失，这可以解释先前报道的此类细胞缺乏趋化性的原因。一个包含翻滚调节剂作为趋化性控制的三组分模型能够解释这些结果。一些膜过程对膜流动性至关重要，而另一些则不然。