Magnetotactic navigation in complex environments

• Applicant: Professor Dr. Stefan Klumpp
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics ; Biophysics ; Microbial Ecology and Applied Microbiology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446142122

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.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partner: Dr. Damien Faivre