Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Proc Natl Acad Sci U S A. 2012 Jun 19;109(25):9869-74. doi: 10.1073/pnas.1120218109. Epub 2012 Jun 7.
Escherichia coli chemotaxis serves as a paradigm for the way living cells respond and adapt to changes in their environment. The chemotactic response has been characterized at the level of individual flagellar motors and in populations of swimming cells. However, it has not been previously possible to quantify accurately the adaptive response of a single, multiflagellated cell. Here, we use our recently developed optical trapping technique to characterize the swimming behavior of individual bacteria as they respond to sudden changes in the chemical environment. We follow the adaptation kinetics of E. coli to varying magnitudes of step-up and step-down changes in concentration of chemoattractant. We quantify two features of adaptation and how they vary with stimulus strength: abruptness (the degree to which return to prestimulus behavior occurs within a small number of run/tumble events) and overshoot (the degree of excessive response before the return to prestimulus behavior). We also characterize the asymmetry between step-up and step-down responses, observed at the single-cell level. Our findings provide clues to an improved understanding of chemotactic adaptation.
大肠杆菌的趋化作用是生物细胞响应和适应环境变化的一个范例。趋化反应已经在单个鞭毛马达和游动细胞群体水平上进行了研究。然而，以前还不可能准确地量化单个多鞭毛细胞的适应性反应。在这里，我们使用我们最近开发的光学捕获技术来描述单个细菌在响应化学环境突然变化时的游动行为。我们跟踪了大肠杆菌对化学引诱物浓度的逐步上升和下降变化的适应动力学。我们量化了适应的两个特征以及它们如何随刺激强度而变化：突然性（在少量的跑/转行为内恢复到刺激前行为的程度）和超调（在恢复到刺激前行为之前过度反应的程度）。我们还描述了在单细胞水平上观察到的上升和下降反应之间的不对称性。我们的发现为深入了解趋化适应提供了线索。
