Control Characteristics of Magnetotactic Bacteria: Magnetospirillum Magnetotacticum Strain MS-1 and Magnetospirillum Magneticum Strain AMB-1

摘要

Magnetotactic bacteria have the potential to execute nontrivial tasks, such as microactuation, micromanipulation, and microassembly, under the influence of the controlled magnetic fields. Closed-loop control characteristics of these magnetic microorganisms depend on their self-propulsion forces (motility) and magnetic dipole moments. These properties can be controlled through the growth conditions of magnetotactic bacteria. We provide a comparison between two species of magnetotactic bacteria, i.e., Magnetospirillum magnetotacticum strain MS-1 and Magnetospirillum magneticum strain AMB-1. This comparison includes the characterization of their morphologies, magnetic dipole moments, and closed-loop control characteristics in the transient and steady states. The characterized average magnetic dipole moments of motile cells of $M$ . magnetotacticum and $M$ . magneticum strains are $1.4times 10^{-16}~{rm A}.{rm m}^{2}$ and $1.5times 10^{-17}~{rm A}.{rm m}^{2}$ at a magnetic field of 7.9 mT, respectively. These magnetic dipole moments are used in the realization of closed-loop control systems for each bacterial strain. The closed-loop control systems achieve point-to-point positioning of $M$ . magnetotacticum cells at an average velocity of ${32pm 10}~mu{rm m}/{rm s}$ (approximately seven body lengths per second), and within an average region of convergence of ${23pm 10}~{mu}{rm m}$ (approx- mately four body lengths), while cells of $M$ . magneticum strain are positioned at an average velocity of ${30pm 12}~mu{rm m}/{rm s}$ (approximately eight body lengths per second), and within an average region of convergence of ${35pm 14}~mu{rm m}$ (approximately 14 body lengths). These results suggest that the cells of $M$ . magnetotacticum strain have a slightly greater tendency to provide desirable closed-loop control characteristics than cells of $M$ . magneticum strain.