Biophysical Society Thematic Meeting | Riga 2026

Active and Responsive Soft Matter: From Biological to Engineered Systems

Poster Abstracts

6-POS Board 6 CONTROLLING MAGNETIC FIELD INDUCED COLLECTIVES OF MAGNETOTACTIC BACTERIA NEAR A WALL Mihails Birjukovs 1 ; Mara Smite 1 ; Damien Faivre 1 ; Andrejs Cebers 1 ; Guntars Kitenbergs 1 ; 1 University of Latvia, Department of Physics, Riga, Latvia Collective effects in microscopic swimmers can be observed due to different stimuli. Magnetotactic bacteria are a type of biological swimmers that can be controlled with an external magnetic field. Ability to control the field allows us to precisely study a variety of conditions applied to the responsive bacteria. Here we report an interesting collective behavior of the magnetotactic bacteria Magnetospirillum gryphiswaldense when exposed to a magnetic field perpendicular to a wall. For a strong enough field bacteria start to interact hydrodynamically, and form thin and round collective structures near the surface. At the same time, bacteria collectively generate a continuous flow, which sucks liquid from the sides of the collective and pushes it away from the surface along the center of the collective structure. We also show that slight bending of the magnetic field, by introducing an in-plane component, results in a controlled motion of the collective along the surface, where the direction of motion follows the left-hand rule. However, if the in-plane component of the magnetic field is too large or the magnetic field is turned off, the collective state gets disassembled. For quantitative results, we apply image processing methods to series of experimental brightfield microscope images of bacteria collectives in microfluidic capillaries, while the phenomenon gets explained with a theoretical model, confirming the predictability of it. These findings could be used to design surface based microrobots for biomedical or similar applications.

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