Chemotactic movement of is one of the most thoroughly studied paradigms
May 2, 2019
Chemotactic movement of is one of the most thoroughly studied paradigms of simple behavior. resulting fine tuning of tumbling angle. Similar strategy is likely to be used by other peritrichously flagellated bacteria, and indicates yet another level of evolutionary development of bacterial chemotaxis. Author Summary Chemotaxis of bacteria plays an important role NVP-LDE225 cost in their life, providing them with the ability to actively search for an optimal growth environment. The chemotaxis system is supposed to be highly optimized, because on the evolutionary time scale even a modest enhancement of its efficiency can give cells a large competitive advantage. For a long time it was believed that the only navigation mechanism of bacteria is increasing the run length toward the preferred direction. The tumble was assumed to be a purely random change of direction between runs. We analysed recently published experimental data that demonstrate a dependence of tumbling angle on the number of CW-switched motors. We introduced such NVP-LDE225 cost a dependence into our model of chemotactic employ temporal comparisons along their runs . Theoretical analysis suggested that such strategy is superior to direct spatial comparisons for objects of bacterial size and swimming speed . Adapted has two swimming modes: runs, which are periods of long straight swimming, and tumbles, when bacterium stops and changes its orientation. The runs of a swimming bacterium are interrupted by tumbles which abruptly change the swimming direction. For cells swimming up an attractant gradient, the runs become longer due to suppression of tumbles, and the cell population migrates KDM3A antibody up the gradient. The frequency of tumbles is controlled by the chemotaxis network through switching of individual motors. During a run, flagellar motors rotate counter-clockwise (CCW) causing flagella to form a bundle, whereas switching of one or several flagellar motors to clockwise (CW) rotation breaks up the bundle and initiates a tumble. The direction of motor rotation depends on the concentration of phosphorylated CheY molecules, which bind to the motor and switch its direction in a highly cooperative mode. The CheY phosphorylation is controlled by the histidine kinase CheA, which forms sensory clusters together with transmembrane receptors and the adaptor CheW. Each receptor can be either active or inactive, depending on ligand binding and on the methylation level. The active receptor activates CheA, eliciting downstream phosphorylation of the response regulator CheY. Phosphorylated CheY (CheYp) is NVP-LDE225 cost dephosphorylated by CheZ. Receptors can be methylated by the methyltransferase CheR and demethylated by the methylesterase CheB. Methylation regulates the receptor activity. Because the reaction of receptor methylation is much slower than the initial response, methylation provides chemical memory, which allows the cell to compare the current ligand concentration with the recent past. Early single-cell tracking experiments reported no dependence of the tumbling angle, i.e. turning angle between consequent runs, on the direction of the gradient and the inclination of a run , and it was thus presumed to be random in subsequent modeling of bacterial chemotaxis. However, in recent study that used high-resolution fluorescence video microscopy , it was shown that the cell turning angle depends on the number of CW-rotating filaments involved in the tumble, and thereby the turning angle rises proportionally to the number of motors that switched to CW rotation. Because the CW switch probability is set by the NVP-LDE225 cost chemotaxis system dependent on the cellular swimming direction along the gradient, the tumbling angle can be expected to depend on the swimming direction, too. If the cell swims up a gradient of attractant, the probability of CW rotation is smaller, and fewer motors are likely to change directions. Therefore, even if the cell makes a tumble, the tumbling angle should be small. When the cell swims down the gradient of attractant, the probability of NVP-LDE225 cost CW rotation is higher and more motors are likely to change directions during a tumble, with the consequence that the tumbling angles will be larger. The goal of this study was thus to investigate the magnitude of the tumbling angle.