PDF(Pubmed)
Abstract：
Bacteria in biofilms secrete potassium ions to attract free swimming cells. However, the basis of chemotaxis to potassium remains poorly understood. Here, using a microfluidic device, we found that Escherichia coli can rapidly accumulate in regions of high potassium concentration on the order of millimoles. Using a bead assay, we measured the dynamic response of individual flagellar motors to stepwise changes in potassium concentration, finding that the response resulted from the chemotaxis signaling pathway. To characterize the chemotactic response to potassium, we measured the dose-response curve and adaptation kinetics via an Förster resonance energy transfer (FRET) assay, finding that the chemotaxis pathway exhibited a sensitive response and fast adaptation to potassium. We further found that the two major chemoreceptors Tar and Tsr respond differently to potassium. Tar receptors exhibit a biphasic response, whereas Tsr receptors respond to potassium as an attractant. These different responses were consistent with the responses of the two receptors to intracellular pH changes. The sensitive response and fast adaptation allow bacteria to sense and localize small changes in potassium concentration. The differential responses of Tar and Tsr receptors to potassium suggest that cells at different growth stages respond differently to potassium and may have different requirements for potassium.
摘要：
生物膜中的细菌分泌钾离子以吸引自由游泳细胞。然而,对钾的趋化性的基础仍然知之甚少。这里,使用微流体装置，我们发现大肠杆菌可以在钾浓度高的地区以毫摩尔的数量级迅速积累。使用珠子测定，我们测量了单个鞭毛马达对钾浓度逐步变化的动态响应，发现反应是由趋化性信号通路引起的。为了表征对钾的趋化反应，我们通过Förster共振能量转移（FRET）测定测量了剂量反应曲线和适应动力学，发现趋化性途径表现出对钾的敏感反应和快速适应。我们进一步发现两种主要的化学感受器Tar和Tsr对钾的反应不同。焦油受体表现出双相反应，而Tsr受体响应钾作为引诱剂。这些不同的反应与两种受体对细胞内pH变化的反应一致。灵敏的反应和快速的适应使细菌能够感知和定位钾浓度的微小变化。Tar和Tsr受体对钾的差异反应表明，处于不同生长阶段的细胞对钾的反应不同，并且对钾的需求可能不同。
