Hydrodynamics and Actuation of Magnetic Bacteria in Confined Geometries:Single cells to swarms

Ohio State University, The, Columbus OH

Investigators

Abstract

In order to navigate their environment, many bacteria and other living micro-organisms swim by rotating a flagellum, a slender helix-shaped attachment connected to the cell body. Near surfaces, the wake produced by this rotating flagellum produces complex forces and torques that act on the bacterium. This gives rise to a range of movements that depend on the orientation of the cell relative to the surface, as well as its rate of rotation and physical geometry. Understanding these interactions at surfaces is important in the study of individual motile bacteria as well as in the development of technologies that can controllably manipulate large micro-organism populations in fluid environments. The proposed investigations will take advantage of the unique features of an inherently magnetic bacterial species, M. magneticum AMB-1, of the magnetotactic bacteria (MTB) group. Their natural magnetism allows them to be externally manipulated, providing a new means of probing the fluid-based forces arising near surfaces. Experiments that explore the role of cell geometry and orientation, magnetic content and flagellar thrust will underlie the development of models for the swimming behavior of MTB and associated fluid flow patterns. MTB are also promising candidate organisms for biologically powered micro-actuation and robotics. In this vein, large scale cell assemblies permit several magnetic field-based devices such as "living liquid crystal" displays and bacterial "conveyor belts" to be developed. The project will undertake outreach activities for several high school teachers in the form of an annual summer workshop. Through these activities, high school students will be able to create a connection between a fun, familiar device, an Xbox controller for example, and concepts in physics, environmental science, biology and engineering disciplines (e.g. magnetism, bacterial habitats, microorganisms, Archimedes principle) in the classroom and laboratory. The realization of functional biology-based robotics at the microscopic level would introduce a paradigm shift in areas as diverse as materials manufacturing, nanotechnology and medicine. The proposed work will make major advances in this direction by investigating fundamental fluid-surface interactions of a model bacterial species (M. magneticum AMB-1) with innate magnetic properties. Together with micro-magnetic and micro-fluidics techniques, their magnetic organelles allow individual living bacteria and swarms be confined and guided to yield quantitative measures of the hydrodynamic and magnetic forces as well as torques that are central to their dynamics. These quantitative parameters will serve as the foundation for developing models of their hydrodynamics on scales ranging from single cells to swarms. Integrating actuation and control of living organisms in low Reynolds number surroundings will serve as the basis to enable several novel biological and bio-hybrid machines that operate in a micro-fluidic environments. The in-situ management of the relative positions of individual cells through designed magnetic surface patterns provides for a novel means to explore pairwise cell-cell interactions that have led to the discovery of novel collective behavior such as rotating filamentary bacterial clusters, living liquid crystal magneto-optical modulators and momentum generating "conveyer-belt" tracks in these environments where viscous forces dominate. The flow fields generated by the propulsion of these flagellated swimmers will be managed to construct microscopically tunable pumps, mixers and hydrodynamic assemblers. The project will undertake stimulating outreach activities for high school students and teachers that link physics, environmental science, biology and engineering disciplines both in the classroom and laboratory.