Chemosensory transduction and the cytoplasmic pathway of Rhodobacter sphaeroides

大多数细菌会游泳，并利用游泳的过程到达它们生长的最佳环境。这可能是植物的根，可能是伤口或肠壁感染，也可能是，例如，生长所需的最佳氧气浓度。细菌太小，无法感知空间梯度，但它们已经开发出一种非常敏感的时间感知系统，可以在大范围的背景浓度范围内感知到小到几个分子的变化。它们感知到这些变化，并向旋转鞭毛马达发出信号，使它们向更好的环境游泳。几十年来，这种敏感性的起源一直困扰着研究人员。利用“主力”细菌大肠杆菌，研究表明，参与感知和转导趋化信号的蛋白质在细胞两极形成了一个非常大的感觉复合体，即大量相互作用的蛋白质。蛋白质相互作用的动力学似乎允许受体适应当前的变化，使邻近的受体能够对未来的变化做出反应。这种蛋白质相互作用的模型允许增加灵敏度，对其他一系列感觉系统也有影响。因此，重要的是，这个模型适用于大肠杆菌以外的物种。许多其他细菌有不止一条途径。这似乎可能使这些物种能够调整它们对当前生长条件的反应，在不同的生长条件下，不同的途径是重要的，如果代谢不会从营养物质的可用性增加中受益，甚至可能阻断来自一条途径的信号。我们感兴趣的是看看情况是否如此，并了解来自不同途径的信号如何整合以产生平衡的反应。我们之前的研究表明，不同途径的蛋白质被靶向，因此它们形成离散的感觉复合物，防止不同途径过早相互作用。用于维持子细胞中正确数量的通路复合物的机制似乎与用于确保细胞在中间分裂的机制有关，并且每个子细胞在分裂时具有正确的细胞质互补。这些数据表明，细菌的发育机制比以前认为的要复杂得多。因此，本研究的一部分将集中于确定化学感觉通路形成的组织机制，确保每个子细胞获得具有正确蛋白质补体的感觉复合物，以便在分裂时每个子细胞都能产生化学感觉反应。大肠杆菌感觉通路对少数分子的敏感性被认为取决于受体的重置，从而允许其他受体现在做出反应。来自其他物种的受体通常与大肠杆菌的受体不同，并且适应区域不易识别。如果同样的系统适用，我们需要确定其他受体上的相关位点，这将成为项目的一部分，测试是否可以为所有细菌的游泳行为开发一个共同的模型。总之，这些数据将表明大肠杆菌化学感觉模型的哪些方面可以扩展到其他细菌物种，在这种情况下球形红杆菌，以及确保子细胞含有相同的DNA和蛋白质的组织机制是否相关，从而允许开发细菌生长的复杂发育模型。

Most bacteria swim, and use that swimming to reach their optimum environment for growth. This could be a plant root, it could be a wound or the gut wall for infection or it could be, for example, the optimum oxygen concentration for growth. Bacteria are too small to sense a spatial gradient, but have developed an exquisitely sensitive temporal sensing system that can sense a change as small as a few molecules over a wide range of background concentrations. They sense these changes and signal to a rotary flagellar motor to bias their swimming towards a better environment. The origins of this sensitivity have puzzled researchers for decades. Using the 'workhorse' bacterium, E.coli, it has been shown that the proteins involved in sensing and transducing the chemotaxis signal form a very large sensory complex, a raft of interacting proteins, at the cell poles. The dynamics of the interactions of the proteins appears to allow the receptors to adapt to current changes, leaving the neighbouring receptors able to respond to future changes. This model of interaction of proteins allowing increased sensitivity has implications for a whole range of other sensory systems. It therefore matters that this model applies to species other than just E.coli. Many other bacteria have more than one pathway. It seems probable that this allows these species to tune their responses to current growth conditions, with the different pathways being important under different growth conditions and perhaps even blocking signals from one pathway if metabolism will not benefit from an increase in availability of that nutrient. We are interested to see whether this is the case, and to understand how the signals from the different pathways integrate to produce a balanced response. Our previous studies showed that the proteins of the different pathways are targetted, so that they form discrete sensory complexes, preventing the different pathways from interacting prematurely. The mechanisms used for maintaining the correct number of pathway complexes in daughter cells on cell division appears to be related to mechanisms used to ensure that the cell divides in the middle, and that each daughter has the correct cytoplasmic compliment on division. These data suggest a much more complex developmental apparatus in bacteria than previously thought. Part of this study will therefore concentrate on identifying the mechanisms involved in organising the formation of the chemosensory pathways, ensuring each daughter cell gets a sensory complex with the right protein complement, so that on division each daughter cell is capable of a chemosensory response. The sensitivity of the E.coli sensory pahway to a few molecules has been suggested to depend on the resetting of the receptors allowing the other receptors to now respond. Receptors from other species are often different from those of E.coli, and the adaptation regions not easily identified. If the same system applies we need to identify related sites on other receptors and this will form part f the project, testing whether a common model can be developed for all bacterial swimming behaviour. Together these data will show which aspects of the E.coli chemosensory model can be extended to other bacterial species, in this case Rhodobacter sphaeroides and whether the organisational mechanisms involved in ensuring daughter cells contain the same DNA and protein are related, allowing a complex developmental model of bacterial growth to be developed.