Limits of feedback control in bacterial chemotaxis.
Limits of feedback control in bacterial chemotaxis.
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DOI：
10.1371/journal.pcbi.1003694
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发表时间：
2014-06
影响因子：
4.3
通讯作者：
Emonet T
中科院分区：
文献类型：
--
作者：
Dufour YS;Fu X;Hernandez-Nunez L;Emonet T
信号通路的输入可能具有复杂的统计数据，这些统计数据取决于环境和对先前刺激的行为反应。这种行为反馈在导航中尤其重要。成功的导航依赖于传感器和执行器之间的正确耦合，传感器在运动过程中收集信息，执行器控制行为。由于重新定向会影响未来的输入，因此行为反馈可以将传感器和执行器置于与静息状态不同的操作状态。那么，生物体如何在不同的环境中保持适当的信息传递呢？在细菌趋化性中，鲁棒性能通常归因于传感器的零积分反馈控制，其保证当输入保持恒定时活性返回到静息状态。虽然这种特性在宽范围的信号强度上提供灵敏度，但仍不清楚其他参数如适应率和适应活性如何影响趋化性能，特别是当考虑到细胞的游泳行为决定输入信号时。我们研究这个问题，结合最近的实验证据，行为反馈和鞭毛运动适应的分析模型和模拟。通过专注于如何最好地利用由响应调节器所携带的感官信息的电机，我们确定了一个操作制度，最大限度地提高漂移速度沿着化学浓度梯度为广泛的环境和传感器的适应率。该最佳方案在运动响应的动态范围之外，但是最大化了运行持续时间向上梯度和向下梯度之间的对比。在陡峭的梯度中，来自趋化漂移的反馈可以推动系统通过分叉。这会产生一种非趋化性状态，除非允许马达适应，否则会捕获细胞。虽然运动适应有帮助，我们发现，随着反馈强度的增加，个体表型不能在所有环境中保持最佳的操作制度，这表明多样性可能是有益的。有偏随机游走是许多生物体用来导航环境的基本策略。沿着期望方向的漂移是通过降低条件改善时重新定向的概率来实现的。在大肠杆菌的趋化系统中，这是通过一个实现负积分反馈控制的感觉模块来实现的，其输出通过响应调节器中继到鞭毛马达（致动器）以控制改变方向的概率。传感器与执行器之间的动态耦合对随机步行者的性能至关重要。在这里，我们确定了这种耦合的最佳方案，可以最大化多种环境中梯度方向上的漂移速度。我们的分析表明，以陡峭梯度反馈到系统上的行为可以通过引起可以将细胞捕获在非趋化状态的双稳态行为来限制单个细胞的性能。这些限制是固有的偏置随机游走策略与积分反馈控制，但可以减轻，如果输出的途径适应，最近表征的鞭毛电机在大肠杆菌。
Inputs to signaling pathways can have complex statistics that depend on the environment and on the behavioral response to previous stimuli. Such behavioral feedback is particularly important in navigation. Successful navigation relies on proper coupling between sensors, which gather information during motion, and actuators, which control behavior. Because reorientation conditions future inputs, behavioral feedback can place sensors and actuators in an operational regime different from the resting state. How then can organisms maintain proper information transfer through the pathway while navigating diverse environments? In bacterial chemotaxis, robust performance is often attributed to the zero integral feedback control of the sensor, which guarantees that activity returns to resting state when the input remains constant. While this property provides sensitivity over a wide range of signal intensities, it remains unclear how other parameters such as adaptation rate and adapted activity affect chemotactic performance, especially when considering that the swimming behavior of the cell determines the input signal. We examine this issue using analytical models and simulations that incorporate recent experimental evidences about behavioral feedback and flagellar motor adaptation. By focusing on how sensory information carried by the response regulator is best utilized by the motor, we identify an operational regime that maximizes drift velocity along chemical concentration gradients for a wide range of environments and sensor adaptation rates. This optimal regime is outside the dynamic range of the motor response, but maximizes the contrast between run duration up and down gradients. In steep gradients, the feedback from chemotactic drift can push the system through a bifurcation. This creates a non-chemotactic state that traps cells unless the motor is allowed to adapt. Although motor adaptation helps, we find that as the strength of the feedback increases individual phenotypes cannot maintain the optimal operational regime in all environments, suggesting that diversity could be beneficial. The biased random walk is a fundamental strategy used by many organisms to navigate their environment. Drift along the desired direction is achieved by reducing the probability to reorient whenever conditions improve. In the chemotaxis system of Escherichia coli, this is accomplished with a sensory module that implements negative integral feedback control, the output of which is relayed to the flagellar motors (the actuators) by a response regulator to control the probability to change direction. The proper dynamical coupling between sensor and actuator is critical for the performance of the random walker. Here, we identify an optimal regime for this coupling that maximizes drift velocity in the direction of the gradient in multiple environments. Our analysis reveals that feedback of the behavior onto the system in steep gradients can constrain individual cell performance, by causing bi-stable behavior that can trap cells in non-chemotactic states. These limitations are inherent in the biased random walk strategy with integral feedback control, but can be alleviated if the output of the pathway adapts, as recently characterized for the flagellar motors in Escherichia coli.
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影响因子：
64.8
作者：
Alon, U;Surette, MG;Leibler, S
通讯作者：
Leibler, S
影响因子：
64.8
作者：
通讯作者：
--
影响因子：
5.6
作者：
Othmer HG;Xin X;Xue C
通讯作者：
Xue C
影响因子：
3.1
作者：
Nicolau, Dan V., Jr.;Armitage, Judith P.;Maini, Philip K.
通讯作者：
Maini, Philip K.
DOI：
10.1073/pnas.1212327109
发表时间：
2012-12-04
影响因子：
11.1
作者：
Lele, Pushkar P.;Branch, Richard W.;Berg, Howard C.
通讯作者：
Berg, Howard C.