Smite Mara, Birjukovs Mihails, Zvejnieks Peteris, Drikis Ivars, Kitenbergs Guntars, Cebers Andrejs
MMML Lab, Department of Physics, University of Latvia (UL), Riga, Latvia.
Department of Physics, University of Latvia (UL), Riga, Latvia.
Biophys J. 2025 Aug 19;124(16):2583-2597. doi: 10.1016/j.bpj.2025.06.008. Epub 2025 Jun 13.
Magnetotactic bacteria (MTB) are a diverse group of microorganisms whose movement can be directed via a magnetic field, which makes them attractive for applications in medicine and microfluidics. One of their key properties is the magnetic moment m, which is challenging to measure. We perform optical imaging experiments with MSR-1 MTB, and derive both the m statistics and the scaling of m with the MTB size using an explicit and fully automated method to determine m from the MTB trajectories via the U-turn protocol, which measures m based on the U-shaped trajectories exhibited by the MTB in an applied alternating magnetic field. The proposed method is an alternative to the standard U-turn time-based moment calculation and uses the theoretical U-turn shape function we have derived. This directly accounts for the U-turn geometry and determines the moment from the U-turn branch width. We couple this approach with a robust U-turn decomposition algorithm that detects U-turns from MTB tracks regardless of their orientations. We report a linear dependence of m on the size of the bacteria, accounting for the bacteria velocity variations during the U-turns. We also show that the new U-turn shape-based and the conventional time-based methods produce significantly different results. The proposed method can be used to differentiate between various types of MTB within the same population based on their velocity and magnetic moments, and to precisely characterize the magnetic properties of a culture.
趋磁细菌（MTB）是一类多样的微生物，其运动可通过磁场引导，这使其在医学和微流体领域具有应用吸引力。它们的一个关键特性是磁矩m，而测量磁矩具有挑战性。我们对MSR - 1趋磁细菌进行光学成像实验，并使用一种明确且完全自动化的方法，通过掉头协议从趋磁细菌的轨迹中确定磁矩，从而得出磁矩的统计数据以及磁矩随趋磁细菌大小的缩放关系。该协议基于趋磁细菌在施加的交变磁场中呈现的U形轨迹来测量磁矩。所提出的方法是标准的基于掉头时间的矩计算方法的替代方法，它使用了我们推导的理论掉头形状函数。这直接考虑了掉头几何形状，并根据掉头分支宽度确定矩。我们将这种方法与一种强大的掉头分解算法相结合，该算法可从趋磁细菌轨迹中检测掉头，而不论其方向如何。我们报告了磁矩与细菌大小的线性关系，同时考虑了掉头过程中细菌速度的变化。我们还表明，基于新的掉头形状的方法和传统的基于时间的方法产生的结果有显著差异。所提出的方法可用于根据同一群体中不同类型趋磁细菌的速度和磁矩进行区分，并精确表征培养物的磁性特性。
