Magnetotactic navigation in complex environments

趋磁细菌在一个专门的细胞器--磁小体链的帮助下在磁场中定位，磁小体链充当细胞内的指南针。在这种情况下，它们的游泳由鞭毛提供动力，由磁场引导；细菌可以被理解为自我推进的指南针。磁力细菌通常生活在水环境的沉积物中，因此在以毛孔和障碍物为特征的环境中游泳。在这个项目中，我们使用理论和实验相结合的方法来定量描述复杂环境中的趋磁运动性。我们调查了在这样的环境中如何实现定向运动，以及这些细菌如何在定向运动的稳健控制和定向灵活性之间取得平衡，以便通过这样的介质导航。我们将使用微流体捕获方法将单个细菌捕获在圆形限制中，并跟踪它们的运动，以研究它们与限制壁的相互作用。基于这些观察，我们将使用理论模型的模拟来预测其他限制几何的行为，以及不同强度和方向的磁场的存在。我们将描述不同种类的趋磁细菌，它们具有不同的趋磁机构，并表现出不同的趋磁行为。因此，我们将获得有关处理限制和阻碍定向运动的障碍的不同策略的信息。我们将反复进行实验和建模，以对实验结果和完全预测的模拟进行定量匹配。此外，我们还将制作带有障碍物的微流体通道，模拟细菌生活的沉积物，并研究趋磁细菌在这些通道中的游泳情况。我们假设，弱磁场将通过提供方向性来增强通过通道的运动，而强磁场可以导致捕获障碍物并阻碍运动。我们将通过实验和模拟来测试这一想法。利用模拟，我们将研究磁制导的相互作用，与障碍物的相互作用，波动，以及在这种环境中的主动方向变化，并设计有趣的障碍物阵列，随后将进行实验测试。我们的目的是通过对不同物种的再比较以及对种群异质性的分析，来推导和测试复杂环境下的导航策略和相应的设计约束。我们的实验方法和理论描述的结合将导致复杂环境中趋磁运动性的全面定量图景，并更广泛地阐明如何在微生物和微型机器人中的复杂环境中平衡方向运动性控制和方向灵活性。

Magnetotactic bacteria orient in magnetic fields with the help of a dedicated organelle, the magnetosome chain, which acts as an intracellular compass needle. In this way, their swimming, powered by their flagella, is guided by the magnetic field; the bacteria can be understood as self-propelled compass needles. Magnetotatic bacteria often live in the sediments of aquatic environments and thus swim in a milieu characterized by pores and obstacles. In this project, we use a combined theoretical and experimental approach for the quantitative characterization of magnetotactic motility in complex environments. We investigate how directional motility is achieved in such an environment and how these bacteria balance robust control of directional motion with directional flexibility to navigate through such a medium. We will trap individual bacteria in circular confinement using a microfluidic trapping approach and track their motion to study their interactions with the confining walls. Based on these observations, we will use simulations of a theoretical model to make predictions for the behavior for other confining geometries and for the presence of magnetic fields of different strengths and orientations. We will characterize different species of magnetotactic bacteria, which have different organizations of their magnetotactic apparatus and exhibit different magnetotactic behaviors. Thereby, we will obtain information about the different strategies of dealing with confinement and obstacles hindering directional motion. We will iterate experiments and modeling to have a quantitative match of the experimental results and fully predictive simulations. In addition, we will make microfluidic channels with obstacles mimicking the sediment the bacteria live in and study the swimming of magnetotactic bacteria through these channels. We hypothesize that weak magnetic fields will enhance the motion through the channel by providing directionality, while strong fields can results in trapping at obstacles and hinder the motion. We will test this idea, both experimentally and in simulations. Using the simulations, we will study the interplay of magnetic guidance, interactions with the obstacles, fluctuations, and active orientation changes in such environments and design interesting arrays of obstacles that will subsequently be tested experimentally. We aim at deducing and testing navigation strategies in complex environments and corresponding design constraints on the magnetotactic apparatus by comparing again different species as well as by an analysis of the population heterogeneity. The combination of our experimental approaches and theoretical description will lead to a comprehensive quantitative picture of magnetotactic motility in complex environments and more generally shed light on how directional control of motility can be balanced with directional flexibility to navigate complex environments in both microorganisms and microrobotics.