Hydrodynamic Clustering of Oriented Magnetotactic Bacteria at Solid-Liquid Interfaces*

Magnetotactic bacteria are a group of motile prokaryotes that synthesize chains of membrane bound intracellular magnetic nanoparticles called magnetosomes. These particles endow the cells with a magnetic moment, which in general lie parallel to the direction of propulsion that is controlled by their rotating flagellar. Thus, the swimming behavior and orientation of the cell relative to surfaces is readily controlled by external magnetic fields. This property makes them an ideal system to investigate the many-body dynamics of self-propelled colloids. In this talk, the self-organization of magnetic bacteria into rotating clusters arising from hydrodynamic cell-cell interactions at solid-liquid interfaces is discussed. The pairwise hydrodynamic interactions are experimentally measured and compared with theoretical calculations. These findings lay the foundation for understanding the many-body dynamics of the clustering process. These hydrodynamically formed clusters are further manipulated by weak in-plane external fields which direct along them along well-defined trajectories and controllably confined with patterned micro-magnetic structures. The implications of these field-controlled phenomena for biology- based applications are discussed.