Magnetotactic bacteria are microorganisms that orient and navigate along the Earth's magnetic field lines, using chains of magnetic nanoparticles embedded in their membranes. These bacteria play an important role in marine ecology and have potential applications in targeted drug delivery. However, their motility and transport in complex porous environments, such as soils or the human vascular network, remain poorly understood. Magnetotactic bacteria have been shown to move collectively as a soliton, i.e., a freely propagating density wave. Yet, these bacteria mostly occupy the seabed, a densely confined and disordered porous medium. Within such disordered media, we expect the onset of arrested phase, similar to Anderson's localization, whereby the disorder leads to a spatial confinement of waves. In the M2 and PhD, we aim to understand the critical level of disorder that triggers a localization transition, using tools from active matter & statistical physics, including an active phase field model. Please also note that: (1) We will work in close collaboration with the group of N. Waisbord, an physicist who is also expert in theoretical modelling. (2) We do not require any previous experience in biology. (3) We are based on the Marseille Luminy, which is arguably the most beautiful campus in the world, located right in the middle of the Calanques National Park.