Zhulin I B, Bespalov V A, Johnson M S, Taylor B L
Department of Microbiology and Molecular Genetics, School of Medicine, Loma Linda University, California 92350, USA.
J Bacteriol. 1996 Sep;178(17):5199-204. doi: 10.1128/jb.178.17.5199-5204.1996.
The microaerophilic nitrogen-fixing bacterium Azospirillum brasilense formed a sharply defined band in a spatial gradient of oxygen. As a result of aerotaxis, the bacteria were attracted to a specific low concentration of oxygen (3 to 5 microM). Bacteria swimming away from the aerotactic band were repelled by the higher or lower concentration of oxygen that they encountered and returned to the band. This behavior was confirmed by using temporal gradients of oxygen. The cellular energy level in A. brasilense, monitored by measuring the proton motive force, was maximal at 3 to 5 microM oxygen. The proton motive force was lower at oxygen concentrations that were higher or lower than the preferred oxygen concentration. Bacteria swimming toward the aerotactic band would experience an increase in the proton motive force, and bacteria swimming away from the band would experience a decrease in the proton motive force. It is proposed that the change in the proton motive force is the signal that regulates positive and negative aerotaxis. The preferred oxygen concentration for aerotaxis was similar to the preferred oxygen concentration for nitrogen fixation. Aerotaxis is an important adaptive behavioral response that can guide these free-living diazotrophs to the optimal niche for nitrogen fixation in the rhizosphere.
微需氧固氮细菌巴西固氮螺菌在氧气的空间梯度中形成了一条界限分明的带。由于趋氧性，细菌被吸引到特定的低氧浓度（3至5微摩尔）区域。从趋氧带游开的细菌会被它们遇到的更高或更低浓度的氧气排斥，并返回该带。通过使用氧气的时间梯度证实了这种行为。通过测量质子动力势监测发现，巴西固氮螺菌的细胞能量水平在氧气浓度为3至5微摩尔时最高。在高于或低于首选氧气浓度的情况下，质子动力势较低。向趋氧带游动的细菌会经历质子动力势的增加，而从趋氧带游开的细菌会经历质子动力势的降低。有人提出，质子动力势的变化是调节正向和负向趋氧性的信号。趋氧性的首选氧气浓度与固氮的首选氧气浓度相似。趋氧性是一种重要的适应性行为反应，可引导这些自由生活的固氮菌到达根际中进行固氮的最佳生态位。
