Laszlo D J, Taylor B L
J Bacteriol. 1981 Feb;145(2):990-1001. doi: 10.1128/jb.145.2.990-1001.1981.
Sensory transduction in aerotaxis required electron transport, in contrast to chemotaxis, which is independent of electron transport. Assays for aerotaxis were developed by employing spatial and temporal oxygen gradients imposed independently of respiration. By varying the step increase in oxygen concentration in the temporal assay, the dose-response relationship was obtained for aerotaxis in Salmonella typhimurium. A half-maximal response at 0.4 microM oxygen and inhibition by 5 mM KCN suggested that the "receptor" for aerotaxis is cytochrome o. The response was independent of adenosine triphosphate formation via oxidative phosphorylation but did correlate with changes in membrane potential monitored with the fluorescent cyanine dye diS-C3-(5). Nitrate and fumarate, which are alternative electron acceptors for the respiratory chain in S. typhimurium, inhibited aerotaxis when nitrate reductase and fumarate reductase were induced. These results support the hypothesis that taxis to oxygen, nitrate, and fumarate is mediated by the electron transport system and by changes in the proton motive force. Aerotaxis was normal in Escherichia coli mutants that were defective in the tsr, tar, or trg genes; in S. typhimurium, oxygen did not stimulate methylation of the products of these genes. A cheC mutant which shows an inverse response to chemoattractants also gave an inverse response to oxygen. Therefore, aerotaxis is transduced by a distinct and unidentified signally protein but is focused into the common chemosensory pathway before the step involving the cheC product. When S. typhimurium became anaerobic, the decreased proton motive force from glycolysis supported slow swimming but not tumbling, indicating that a minimum proton motive force was required for tumbling. The bacteria rapidly adapted to the anaerobic condition and resumed tumbling after about 3 min. The adaptation period was much shorter when the bacteria had been previously grown anaerobically.
与不依赖电子传递的趋化作用相反，趋氧性中的感觉转导需要电子传递。通过利用独立于呼吸作用施加的空间和时间氧梯度，开发了趋氧性测定方法。通过改变时间测定中氧浓度的逐步增加，获得了鼠伤寒沙门氏菌趋氧性的剂量反应关系。在0.4微摩尔氧时出现半数最大反应，且受5毫摩尔氰化钾抑制，这表明趋氧性的“受体”是细胞色素o。该反应独立于通过氧化磷酸化形成的三磷酸腺苷，但确实与用荧光花青染料diS-C3-(5)监测的膜电位变化相关。硝酸盐和富马酸盐是鼠伤寒沙门氏菌呼吸链的替代电子受体，当硝酸盐还原酶和富马酸盐还原酶被诱导时，它们会抑制趋氧性。这些结果支持这样的假设，即对氧、硝酸盐和富马酸盐的趋化作用是由电子传递系统和质子动力势的变化介导的。在tsr、tar或trg基因有缺陷的大肠杆菌突变体中，趋氧性正常；在鼠伤寒沙门氏菌中，氧不会刺激这些基因产物的甲基化。对化学引诱剂表现出反向反应的cheC突变体对氧也有反向反应。因此，趋氧性是由一种独特且未鉴定的信号蛋白转导的，但在涉及cheC产物的步骤之前，它会集中到共同的化学感受途径中。当鼠伤寒沙门氏菌变为厌氧时，糖酵解产生的降低的质子动力势支持缓慢游动但不支持翻滚，这表明翻滚需要最小的质子动力势。细菌迅速适应厌氧条件，并在约3分钟后恢复翻滚。当细菌先前在厌氧条件下生长时，适应期要短得多。
