ADAPTATION KINETICS IN BACTERIAL CHEMOTAXIS
ADAPTATION KINETICS IN BACTERIAL CHEMOTAXIS
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DOI：
10.1128/jb.154.1.312-323.1983
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发表时间：
1983-01-01
影响因子：
3.2
通讯作者：
BERG, HC
中科院分区：
文献类型：
--
作者：
BLOCK, SM;SEGALL, JE;BERG, HC
用单个鞭毛将大肠杆菌细胞系在玻璃上，使其经受含有引诱剂α-β的培养基的恒定流动。甲基-DL-天冬氨酸该化学品的浓度在跨越化学感受器的解离常数的范围内用可编程混合装置以与在空间梯度中游泳的细胞所经历的速率相当的速率变化。当打开指数增加的斜坡（线性增加化学感受器占有率的斜坡）时，细胞的旋转偏差（逆时针旋转所花费的时间分数）迅速变化到更高的稳定水平，并持续斜坡的持续时间。偏压的变化随斜坡速率而增加，即，与化学感受器占有率的时间变化率有关。这种行为可以通过涉及比例控制的适应模型来解释，其中鞭毛马达响应于与最近过去的平均占有率和当前占有率之间的差异成比例的误差信号。顺时针和逆时针旋转间隔的分布是指数的。这一结果不能解释的响应调节器模型，其中旋转状态之间的转换所产生的阈值交叉的监管机构受到统计波动，这种机制产生的分布太多的长事件。数据可以通过一个模型拟合，其中旋转状态之间的转换由一阶速率常数决定。误差信号用作偏置调节器，控制这些常数的值。
Cells of Escherichia coli, tethered to glass by a single flagellum, were subjected to constant flow of a medium containing the attractant .alpha.-methyl-DL-aspartate. The concentration of this chemical was varied with a programmable mixing apparatus over a range spanning the dissociation constant of the chemoreceptor at rates comparable to those experienced by cells swimming in spatial gradients. When an exponentially increasing ramp was turned on (a ramp that increases the chemoreceptor occupancy linearly), the rotational bias of the cells (the fraction of time spent spinning counterclockwise) changed rapidly to a higher stable level, which persisted for the duration of the ramp. The change in bias increased with ramp rate, i.e., with the time rate of change of chemoreceptor occupancy. This behavior can be accounted for by a model for adaptation involving proportional control, in which the flagellar motors respond to an error signal proportional to the difference between the current occupany and the occupancy averaged over the recent past. Distributions of clockwise and counterclockwise rotation intervals are exponential. This result cannot be explained by a response regulator model in which transitions between rotational states are generated by threshold crossings of a regulator subject to statistical fluctuation; this mechanism generates distributions with far too many long events. The data can be fit by a model in which transitions between rotational states are governed by first-order rate constants. The error signal acts as a bias regulator, controlling the values of these constants.