Using Microfluidics to Study Magnetotactic Bacteria

Abstract

The purpose of this thesis was to investigate the swimming behavior of magnetotactic bacteria 1) in flow conditions and 2) in porous media; and further 3) to exploit their unique characteristics towards bio-actuation of small droplets. Bacteria are found in every habitable niche on Earth. In their planktonic lifestyle they often inhabit dynamic environments where their motility is influenced by flow and the proximity to different surfaces. Recently, considerable interest has been demonstrated in the use of bacteria to perform complex tasks, such as carrying cargo for targeted drug delivery. Magnetotactic bacteria (MTB) found in both freshwater and marine environments can orient to, and swim along, the geomagnetic field lines, a behavior called magnetotaxis. While foraging in their native habitats, their ultimate swimming path originates from the competition between magnetotaxis and hydrodynamic influences related to flow and nearby surfaces. MTB have advantages over other bacteria as microbiorobots for controlled transport due to their motility and steerability. However, how MTB interact with complex environments in aquatic environments has remained poorly defined. Therefore, to better exploit the abilities of MTB for in vivo applications, understanding their behavior in relevant environments is crucial. By using microfluidics and microscopy techniques, I have demonstrated in this thesis that magnetotaxis enables directed motion of Magnetospirillum magneticum over long distances in flow conditions relevant to both aquatic environments and biomedical applications. These MTB can overcome higher flow velocities when directed to swim perpendicular to the flow as compared to upstream. In addition, I showed that magnetotaxis enables MTB to migrate effectively through both homogenous and heterogeneous porous micromodels, interacting with obstacles and overcoming tortuous flow fields. These results bring new insight into MTB navigation in environments similar to their natural habitats, and their potential in vivo applications as microbiorobots. Lastly, I have presented a biologically-driven magnetic actuation of droplets on a superhydrophobic surface using MTB. With magnetotaxis for navigation, it is possible to harness MTB to transport microdroplets, thus suggesting their potential for lab-on-a-chip applications.