Integrated Global and Local Field Sensing in Magnetospirillum Magnetotacticum

Abstract

The ability for organisms to evolve specialized functions is often correlated to unique intracellular structures, non-obvious to typical biological systems. One example is the biosynthesis of magnetic particles. Biology has evolved important magnetic sensing structures in a range of organisms from radula teeth in the chiton, algae, honeybees homing pigeons and humans. Unicellular organisms also have this ability in the case of magnetotactic bacteria, but here we show an even more intriguing finding, which is that Magnetospirillum Magnetotacticum strain AMB-1 have both a global sensing system for magnetic fields as well as a localize sensing that has intensity sensitivity. To investigate this global and local intensity based magnetic field response, permalloy microfabricated structures and a pair of Helmholtz coils were custom-built to induce localized control of the magnetotactic bacteria. In the global sense, at low fields these bacteria have the choice to follow the magnetic field lines or to meander around without following the magnetic field lines until about 11 Oe when about 90% of the bacteria seem to align with the field and thus begin to act as actuators rather than as biological sensors. When they were exposed to localize magnetic fields, these 2-3 micrometer organisms would deflect their motility paths to sense very small magnetic fields as well. Furthermore, when the AMB-1 sense local gradients, interestingly there is a bifurcation in response. Faster moving bacteria will deflect their direction based upon sensing local magnetic field gradients, but slower moving bacteria will either reverse their directions or perform multiple oscillations around specific sharp gradients and then continue swimming in the original direction. We believe that these results have implications ranging from synthetic biology to biologically inspired nanostructures to evolutionary biology.