Measurement of the magnetic moment of single Magnetospirillum gryphiswaldense cells by magnetic tweezers

Abstract

Magnetospirillum gryphiswaldense is a helix-shaped magnetotactic bacterium that synthesizes iron-oxide nanocrystals, which allow navigation along the geomagnetic field. The bacterium has already been thoroughly investigated at the molecular and cellular levels. However, the fundamental physical property enabling it to perform magnetotaxis, its magnetic moment, remains to be elucidated at the single cell level. We present a method based on magnetic tweezers; in combination with Stokesian dynamics and Boundary Integral Method calculations, this method allows the simultaneous measurement of the magnetic moments of multiple single bacteria. The method is demonstrated by quantifying the distribution of the individual magnetic moments of several hundred cells of M. gryphiswaldense. In contrast to other techniques for measuring the average magnetic moment of bacterial populations, our method accounts for the size and the helical shape of each individual cell. In addition, we determined the distribution of the saturation magnetic moments of the bacteria from electron microscopy data. Our results are in agreement with the known relative magnetization behavior of the bacteria. Our method can be combined with single cell imaging techniques and thus can address novel questions about the functions of components of the molecular magnetosome biosynthesis machinery and their correlation with the resulting magnetic moment.

Microbe‐Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

“…Through more accurate and comprehensive detection, this method offers a better understanding on navigational mechanism that involves magnetotaxis. [ 59 ] Ferromagnetic resonance spectroscopy may be used to detect magnetic anisotropy, another important characteristic of MTB. Detection of the magnetic anisotropy of magnetofossils enables better understanding of microbe ecology throughout evolution.…”

Chemotaxis in external fields: Simulations for active magnetic biological matter

“…We show that forces improve chemotaxis for angles smaller than 90˚and totally hinder it for values higher than a threshold value (Fig 2b), for both run and reverse and run and tumble motions. This could be of particular interest when considering bacteria or biohybrids actuated and directed by external forces, such as magnetic swimmers in a magnetic gradient [17] and under the influence of magnetic tweezers [39], or when considering chemotactic swimmers inside a fluid flow [36,52], for which previous studies ignored the complexity given by chemotactic behaviors.…”

“…A gradient of a chemoattractant biases this random walk up the gradient with velocity v taxis ' 1.08 μms −1 (Fig 2a). As a first simple example for the influence of an external field, we consider a constant external force, which might represent a force applied by the flow of the fluid in which the swimmer moves, or by optical or magnetic tweezers onto the swimmer [39]. Under a constant force, the run and tumble trajectories become biased (stretched out) in the direction of the force.…”

The behavior of magnetotacticbacteria in changing magnetic fields

“…The response of bacteria to external fields by means of U-turns and rotations has been modelled and used to determine their properties (Pichel et al, 2018;Esquivel and Lins de Barros, 1986;Zahn et al, 2017). Alignment of a bacterium to an external magnetic field with angle θ(t ) can be described by the following differential equation:…”