occurrence and microscopic analyses of multicellular magnetotactic prokaryotes from coastal sediments in the Yellow Sea

Multicellular magnetotactic prokaryotes （MMPs） are a group of aggregates composed of 7-45 gram-negative cells synthesizing intracellular magnetic crystals. Although they are thought to be globally distributed, MMPs have been observed only in marine environments in America and Europe. Most MMPs share a rosette-like morphology and biomineralize iron sulfide crystals. In the present study, abundant MMPs were observed, with a density of 26 ind./cm^3, in the sediments of a coastal lagoon, Lake Yuehu, in the Yellow Sea. Optical microscopy showed that all of them were rosette shaped with a diameter of 5.5±0.8 μm. Transmission electron microscopy revealed that these MMPs were composed of 10- 16 ovoid cells and flagellated peritrichously. High-resolution transmission electron microscopy and energy dispersive X-ray analysis indicated that they biomineralized bullet-shaped magnetite crystals in highly organized parallel chains within which the magnetosomes were oriented in the same direction. This is the first report of MMPs from Asia and demonstrates the ubiquitous distribution of MMPs.

Avian magnetoreception model realized by coupling a magnetite-based mechanism with a radical-pair-based mechanism

Many animal species have been proven to use the geomagnetic field for their navigation, but the biophysical mechanism of magnetoreception has remained enigmatic. In this paper, we present a special biophysical model that consists of magnetite-based and radical-pair-based mechanisms for avian magnetoreception. The amplitude of the resultant magnetic field around the magnetic particles corresponds to the geomagnetic field direction and affects the yield of singlet/triplet state products in the radical-pair reactions. Therefore, in the proposed model, the singlet/triplet state product yields are related to the geomagnetic field information for orientational detection. The resultant magnetic fields corresponding to two materials with different magnetic properties are analyzed under different geomagnetic field directions. The results show that ferromagnetic particles in organisms can provide more significant changes in singlet state products than superparam- agnetic particles, and the period of variation for the singlet state products with an included angle in the geomagnetic field is approximately 180 when the magnetic particles are ferromagnetic materials, consistent with the experimental results obtained from the avian magnetic compass. Further, the calculated results of the singlet state products in a reception plane show that the proposed model can explain the avian magnetoreception mechanism with an inclination compass.

Dynamic Model and Motion Mechanism of Magnetotactic Bacteria with Two Lateral Flagellar Bundles

Magnetotactic Bacteria （MTB） propel themselves by rotating their flagella and swim along the magnetic field lines. To analyze the motion of MTB, MTB magneto-ovoid strain MO-1 cells, each with two bundles of flagella, were taken as research object. The six-degrees-of-freedom （6-DoF） dynamic model of MO-1 was established based on the Newton-Euler dynamic equations. In particular, the interaction between the flagellum and fluid was considered by the resistive force theory. The simulated motion trajectory of MTB was found to consist of two kinds of helices： small helices restilting from the imbalance of force due to flagellar rotation, and large helices arising from the different directions of the rotation axis of the cell body and the propulsion axis of the flagellum. The motion behaviours of MTB in various magnetic fields were studied, and the simulation results agree well with the experiment results. In addition, the rotation frequency of the flagella was estimated at 1100 Hz, which is consistent with the average rotation rate for Na^＋-driven flagellar motors. The included angle of the magnetosome chain was predicted at 40° that is located within 20° to 60° range of the observed results. The results indicate the correctness of the dynamic model, which may aid research on the operation and control of MTB-propelled micro-actuators. Meanwhile, the motion behaviours of MTB may inspire the development of micro-robots with new driving mechanisms.

Assessing bacterial magnetotactic behavior by using permanent magnet blocks

Assessing the movement of magnetotactic bacteria(MTB)under magnetic fields is a key to exploring the function of the magnetotaxis.In this study,a simple method was used to analyze the behavior of MTB,which was based on the accumulation of cells on the walls of a test tube when two permanent magnet blocks were applied on the tube.Experimental results showed a significant difference among the movements of the polar MTB,axial MTB,and ferrofluid.The polar magnetotactic cells aggregated as spots above or below the two magnet blocks besides the aggregated spots underneath the magnet blocks.By contrast,the axial magnetotactic cells aggregated only as two round spots underneath the magnet blocks,and more cells aggregated in the center than all around of the spot.For the ferrofluid,two spots were also formed underneath the magnet blocks,and the aggregated particles formed a ring shape.Magnetic calculation by finite element method was used to analyze the phenomenon,and the findings were reasonably explained by the MTB features and magnetic field theory.A scheme that differentiates polar MTB,axial MTB,and magnetic impurity could be developed,which would be beneficial to fieldworks involving MTB in the future.