Molecular mechanisms of bacterial magneto-aerotaxis

趋磁细菌（MTB）拥有利用地球磁场导航的独特能力。磁导航是基于磁小体合成的细胞的被动磁排列，细胞内膜包裹的磁性铁矿物晶体呈链状排列，以及利用鞭毛的主动运动。磁排列被认为可以促进水生栖息地中有利于生长的氧浓度的定向，这种行为被称为趋磁性。然而，控制这种独特运动模式的分子机制与大肠杆菌等被充分研究的模式生物有很大不同，人们对其知之甚少。特别是，目前尚不清楚磁场和氧梯度的感知是否以及如何通过MTB中复杂的化学感觉网络来控制鞭毛运动输出。为了研究细菌趋磁性的分子机制，我在遗传易感的极鞭毛结核杆菌gryphiswaldense Magnetospirillum建立了鞭毛荧光标记。在提议的项目中，这种方法将用于确定化学感觉系统如何协调磁螺旋体中的鞭毛马达-这是一个尚未解决的问题，并且已经假设了相互矛盾的模型（包括非磁性双极性鞭毛螺旋体），例如在相反的感觉中相反的鞭毛马达旋转，在相同的方向上，或马达暂停。额外的目标将是揭示环境信号和参数（如氧梯度、环境磁场或环境结构）如何影响鞭毛运动输出、鞭毛的极性组装和磁场中的定向运动性（所谓的向北/向南磁致航性）。最终，这个项目将在理解控制细菌磁性导航的分子原理方面取得突破。预期的研究结果还将对细菌运动和微生物细胞生物学产生更广泛的影响，如复杂的细菌信号转导系统、极地鞭毛的鞭毛组装和运动控制（包括许多临床相关的病原体），以及群体异质性和不同的运动模式如何与复杂环境中的选择优势相关。最后，对磁致航性的全面理解可能为未来在合成生物学中的应用打开大门，例如MTB的靶向修饰和微机器人应用的磁导航工程。

Magnetotactic bacteria (MTB) possess the unique ability to navigate using the Earth’s magnetic field. Magnetic navigation results from the passive magnetic alignment of cells based on the synthesis of magnetosomes, intracellular membrane-enveloped crystals of a magnetic iron mineral arranged in chains, and active motility utilizing flagella. Magnetic alignment is believed to facilitate orientation within aquatic habitats towards growth-favoring oxygen concentrations, a behavior known as magneto-aerotaxis. However, the molecular mechanisms controlling this unique motility pattern, which differs significantly from those of well-studied model organisms like Escherichia coli, are poorly understood. In particular, it is unknown if and how the perception of magnetic fields and oxygen gradients is integrated via the complex chemosensory network in MTB to control flagellar motor output. To study the molecular mechanisms of bacterial magneto-aerotaxis, I established fluorescent labeling of flagella in the genetically tractable polarly flagellated MTB Magnetospirillum gryphiswaldense. In the proposed project, this method will be used to determine how the chemosensory system coordinates flagellar motors in magnetospirilla - a question that has not been solved and for which contradicting models have been postulated (including non-magnetic bipolarly flagellated spirilla), such as the rotation of opposing flagellar motors in opposite senses, in the same direction, or pausing of motors. Additional aims will be to unravel how environmental signals and parameters (such as the oxygen gradient, the ambient magnetic field, or the environmental structure) affect flagellar motor output, polar assembly of flagella, and directional motility in magnetic fields (so-called North-/South-seeking magneto-aerotaxis). Ultimately, this project will yield a breakthrough in the understanding of the molecular principles that govern magnetic navigation in bacteria. Expected findings will also have broader implications related to bacterial motility and microbial cell biology, such as complex bacterial signal transduction systems, flagellar assembly and motor control in polar flagellates (including many clinically relevant pathogens), and how population heterogeneity and different motility patterns relate to the selective advantage in complex environments. Finally, a comprehensive understanding of magneto-aerotaxis may open the door for future applications in synthetic biology, such as the targeted modification of MTB and the engineering of magnetic navigation for microrobotic applications.