The fast tumble signal in bacterial chemotaxis
The fast tumble signal in bacterial chemotaxis
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DOI：
10.1529/biophysj.103.033043
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发表时间：
2004-06-01
影响因子：
3.4
通讯作者：
Trentham, DR
中科院分区：
文献类型：
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作者：
Khan, S;Jain, S;Trentham, DR
我们已经分析了在大肠杆菌中通过闪光光释放不耐光前体的亮氨酸来处理排斥信号的过程。我们发现：1)游动细胞群的反应幅度随亮氨酸跳跃浓度的增加而增加，表观希尔系数为1.3，半最大剂量为14.4um：2)在0-0.5 mM的亮氨酸浓度跃升足以获得饱和运动反应时，接近0.05 S的游动细胞反应时间比用单个鞭毛拴在石英盖片上测得的0.39+/-0.18 S的运动反应时间快数倍；(3)单个细胞的运动反应时间与旋转偏差有关，而与细胞大小无关。这些结果提供了在排斥信号处理过程中放大、限速步骤和鞭毛束机制的信息。兴奋反应的半最大剂量与报道的适应的对应值之间的差异提供了对CheYP形成速度的估计，CheYP是信号蛋白Chey的磷酸化形式。估计的增加使受体激酶偶联比率的下限为6.0。运动反应时间分布的大小和形式表明，它是由刺激后转换概率而不是CheYP周转、扩散或绑定决定的。系留细胞和游动细胞对驱避剂的反应时间之间的时间差异可以定量地解释，这表明一个鞭毛足以引起细菌游泳方向的可测量变化。
We have analyzed repellent signal processing in Escherichia coli by flash photorelease of leucine from photolabile precursors. We found that 1), response amplitudes of free-swimming cell populations increased with leucine jump concentration, with an apparent Hill coefficient of 1.3 and a half-maximal dose of 14.4 muM; 2), at a 0-0.5 mM leucine concentration jump sufficient to obtain a saturation motile response, the swimming cell response time of similar to0.05 s was several-fold more rapid than the motor response time of 0.39 +/- 0.18 s measured by following the rotation of cells tethered by a single flagellum to quartz coverslips; and 3), the motor response time of individual cells was correlated with rotation bias but not cell size. These results provide information on amplification, rate-limiting step, and flagellar bundle mechanics during repellent signal processing. The difference between the half-maximal dose for the excitation response and the corresponding value reported for adaptation provides an estimate of the increase in the rate of formation of CheYP, the phosphorylated form of the signal protein CheY. The estimated increase gives a lower limit receptor kinase coupling ratio of 6.0. The magnitude and form of the motor response time distribution argue for it being determined by the poststimulus switching probability rather than CheYP turnover, diffusion, or binding. The temporal difference between the tethered and swimming cell response times to repellents can be quantitatively accounted for and suggests that one flagellum is sufficient to cause a measurable change of direction in which a bacterium swims.