Department of Biochemistry, University of Tennessee, Knoxville, TN 37996, USA.
Proc Natl Acad Sci U S A. 2010 Feb 2;107(5):2235-40. doi: 10.1073/pnas.0910055107. Epub 2010 Jan 19.
Chemoreceptors provide sensory specificity and sensitivity that enable motile bacteria to seek optimal positions for growth and metabolism in gradients of various physicochemical cues. Despite the abundance of chemoreceptors, little is known regarding the sensory specificity and the exact contribution of individual chemoreceptors to the lifestyle of bacteria. Azospirillum brasilense are motile bacteria that can fix atmospheric nitrogen under microaerophilic conditions. Here, we characterized a chemoreceptor in this organism, named AerC, which functions as a redox sensor that enables the cells to seek microaerophilic conditions that support optimum nitrogen fixation. AerC is a representative of a widespread class of soluble chemoreceptors that monitor changes in the redox status of the electron transport system via the FAD cofactor associated with its PAS domains. In A. brasilense, AerC clusters at the cell poles. Its cellular localization and contribution to the behavioral response correlate with its expression pattern and with changes in the overall cellular FAD content under nitrogen-fixing conditions. AerC-mediated energy taxis in A. brasilense prevails under conditions of nitrogen fixation, illustrating a strategy by which cells optimize chemosensing to signaling cues that directly affect current metabolic activities and thus revealing a mechanism by which chemotaxis is coordinated with dynamic changes in cell physiology.
化感受体提供了感官特异性和敏感性，使运动细菌能够在各种物理化学线索的梯度中寻找最佳的生长和代谢位置。尽管化感受体丰富，但对于感官特异性和单个化感受体对细菌生活方式的确切贡献知之甚少。固氮螺菌是一种可以在微氧条件下固定大气氮的运动细菌。在这里，我们对该生物体中的一种化感受体进行了表征，命名为 AerC，它作为一种氧化还原传感器，使细胞能够寻找支持最佳氮固定的微氧条件。AerC 是一类广泛存在的可溶性化感受体的代表，通过与其 PAS 结构域相关的 FAD 辅因子监测电子传递系统氧化还原状态的变化。在固氮螺菌中，AerC 聚集在细胞的两极。它的细胞定位和对行为反应的贡献与其表达模式以及在氮固定条件下整个细胞 FAD 含量的变化相关。AerC 介导的固氮螺菌中的能量趋化作用在氮固定条件下占主导地位，说明了细胞优化化学感应以响应直接影响当前代谢活动的信号的策略，从而揭示了趋化性与细胞生理学动态变化相协调的机制。
