The magnetotactic yet uncultured species ‘Candidatus Magnetoglobus multicellularis’ is a spherical, multicellular ensemble of bacterial cells able to align along magnetic field lines while swimming propelled by flagella. Magnetotaxis is due to intracytoplasmic, membrane-bound magnetic crystals called magnetosomes. The net magnetic moment of magnetosomes interacts with local magnetic fields, imparting the whole microorganism a torque. Previous works investigated ‘Ca. M. multicellularis’ behavior when free swimming in water; however, they occur in sediments where bumping into solid particles must be routine. In this work, we investigate the swimming trajectories of ‘Ca. M. multicellularis’ close to solid boundaries using video microscopy. We applied magnetic fields 0.25–8.0 mT parallel to the optical axis of a light microscope, such that microorganisms were driven upwards towards a coverslip. Because their swimming trajectories approach cylindrical helixes, circular profiles would be expected. Nevertheless, at fields 0.25–1.1 mT, most trajectory projections were roughly sinusoidal, and net movements were approximately perpendicular to applied magnetic fields. Closed loops appeared in some trajectory projections at 1.1 mT, which could indicate a transition to the loopy profiles observed at magnetic fields ≥ 2.15 mT. The behavior of ‘Ca. M. multicellularis’ near natural magnetic grains showed that they were temporarily trapped by the particle’s magnetic field but could reverse the direction of movement to flee away. Our results show that interactions of ‘Ca. M. multicellularis with solid boundaries and magnetic grains are complex and possibly involve mechano-taxis.

趋磁但未培养的物种' Candidatus Magnetoglobus multicellularis'是一种球形的多细胞细菌细胞群，能够在鞭毛推动下游泳时沿着磁场线排列。趋磁性是由于称为磁小体的胞质内膜结合磁性晶体。磁小体的净磁矩与局部磁场相互作用，赋予整个微生物一个扭矩。以前的作品调查了' Ca。多细胞分枝杆菌在水中自由游泳时的行为；然而，它们发生在沉积物中，撞到固体颗粒必须是常规的。在这项工作中，我们研究了 ' Ca的游泳轨迹。M. multicellularis 使用视频显微镜接近固体边界。我们施加了 0.25-8.0 mT 的磁场，平行于光学显微镜的光轴，这样微生物就被向上推向盖玻片。因为它们的游泳轨迹接近圆柱形螺旋线，所以预计会出现圆形轮廓。然而，在 0.25-1.1 mT 的场中，大多数轨迹投影大致是正弦曲线，净运动大致垂直于施加的磁场。闭环出现在 1.1 mT 的一些轨迹投影中，这可能表明在磁场 ≥ 2.15 mT 时观察到的环形轮廓的过渡。' Ca的行为。M. multicellularis 附近的天然磁性颗粒表明，它们暂时被粒子的磁场困住了，但可以逆转运动方向逃跑。我们的结果表明 ' Ca 的相互作用。具有固体边界和磁性颗粒的多细胞分枝杆菌很复杂，可能涉及机械趋向性。