Molecular mechanisms of bacterial magneto-aerotaxis

趋磁细菌(MTB)具有利用地球磁场导航的独特能力。磁性导航的结果是基于磁小体的合成的细胞的被动磁排列，细胞内以链状排列的磁性铁矿物的膜包裹的晶体，以及利用鞭毛的主动运动。磁排列被认为有助于在水生栖息地内向有利于生长的氧气浓度定向，这种行为被称为磁悬浮。然而，控制这种独特的运动模式的分子机制，与那些研究得很好的模式生物，如大肠杆菌，却知之甚少。特别是，目前尚不清楚磁场和氧气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马达输出。为了研究细菌磁-空气趋性的分子机制，我在遗传易驯化的极鞭毛结核杆菌中建立了鞭毛的荧光标记。在拟议的项目中，这一方法将用于确定化学传感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，并为其假定了相互矛盾的模型(包括非磁性双极鞭毛螺旋体)，例如相对的鞭毛马达在相反的感觉下以相同的方向旋转，或马达的停顿。其他目标将是揭示环境信号和参数(如氧气梯度、环境磁场或环境结构)如何影响鞭毛马达输出、鞭毛的极地组装和磁场中的定向运动性(所谓的北/南寻觅磁气性)。最终，该项目将在理解控制细菌磁导航的分子原理方面取得突破。预期的发现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、极鞭毛虫(包括许多临床相关的病原体)中的鞭毛组装和运动控制，以及种群异质性和不同的运动模式如何与复杂环境中的选择优势有关。最后，对磁悬浮的全面了解可能会为未来在合成生物学中的应用打开大门，例如MTB的靶向修饰和微型机器人应用的磁性导航工程。

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.