Department of Physics, Bangalore University, Bengaluru, 560056, India.
Department of Physics, Government First Grade College, Chickballapura, 562101, India.
J Biol Phys. 2021 Mar;47(1):79-93. doi: 10.1007/s10867-021-09566-9. Epub 2021 Mar 9.
We investigate through simulations the phenomena of magnetoreception to enable an understanding of the minimum requirements of a fail-safe mechanism, operational at the cellular level, to sense a weak magnetic field at ambient temperature in a biologically active environment. To do this, we use magnetotactic bacteria (MTB) as our model system. The magnetic field sensing ability of these bacteria is due to the presence of magnetosomes, which are internal membrane-bound organelles that contain an iron-based magnetic mineral crystal. These magnetosomes are usually found arranged in a chain aligned with the long axis of the bacterial body. This arrangement yields an overall magnetic dipole moment to the bacterial cell. To simulate this orientation process, we set up a rotational Langevin stochastic differential equation and solve it repeatedly over appropriate time steps for isolated spherical shaped MTB as well as for a more realistic model of spheroidal MTB with flagella. The orientation process appears to depend on shape parameters with spheroidal MTB showing a slower response time compared to spherical MTB. Further, our simulation also reveals that the alignment to the external magnetic field is more robust for an MTB when compared to single magnetosome. For the simulation involving magnetosomes, we include an extra torque that arises from the twisting of an attachment tether and enhance the viscosity of the surrounding medium to mimic intracellular conditions in the governing Langevin equation. The response time of alignment is found to be substantially reduced when one includes a dipole interaction term with a neighboring magnetosome and the alignment becomes less robust with increase in inter dipole distance. The alignment process can thereby be said to be very sensitively dependent on the distance between magnetosomes. Simulating the process of alignment between two neighboring magnetosomes, both in the absence and presence of an ambient magnetic field, we conclude that alignment between these dipoles at the distances typical in an MTB is highly probable and it would be the locked unit that responds to changes in the external magnetic field.
我们通过模拟研究了磁受体现象，以便理解在生物活性环境中，在细胞水平上运行的、能感知弱磁场的故障保护机制的最低要求。为此，我们使用趋磁细菌（MTB）作为模型系统。这些细菌的磁场感应能力归因于磁小体的存在，磁小体是内部膜结合的细胞器，包含铁基磁性矿物晶体。这些磁小体通常排列成与细菌体长轴一致的链状。这种排列使细菌细胞具有整体磁偶极矩。为了模拟这种取向过程，我们建立了一个旋转朗之万随机微分方程，并在适当的时间步长内重复求解，针对孤立的球形 MTB 以及具有鞭毛的更现实的球形 MTB 模型。取向过程似乎取决于形状参数，与球形 MTB 相比，球形 MTB 的响应时间较慢。此外，我们的模拟还表明，与单个磁小体相比，MTB 对外部磁场的定向更为稳健。对于涉及磁小体的模拟，我们在控制朗之万方程中添加了一个额外的扭矩，该扭矩源于连接体的扭曲以及增强周围介质的粘度，以模拟细胞内条件。当包括与相邻磁小体的偶极相互作用项时，对齐的响应时间会大大减少，并且随着偶极距离的增加，对齐的稳健性会降低。因此，可以说，对齐过程非常依赖于磁小体之间的距离。模拟两个相邻磁小体之间的对齐过程，无论是在没有还是存在环境磁场的情况下，我们得出的结论是，在 MTB 中典型距离处这些偶极体之间的对齐非常可能，并且响应外部磁场变化的将是锁定单元。
