Magnetotactic bacteria (MTB) are Gram-negative, motile prokaryotes that synthesize intracellular crystals of magnetic iron oxide (magnetite) or iron sulfide (greigite) minerals. These apparently nanometer-sized, membrane-bounded crystals are called magnetosomes and cause the bacteria to orient and migrate along geomagnetic field lines.
Magnetosomes in MTB are of great importance in understanding biomineralization and possible links between organisms and geomagnetic field. Fossil magnetosomes (magnetofossils) are ubiquitous in sediments and significantly contribute to magnetic signals. Magnetofossils have been used as biosignature of the Martian meteorite. Bacterial magnetites are also of great potential applications in modern biological and medical sciences.

  Current exploring topics:

    1. The biomineralization and magnetic properties of bacterial magnetite

To understand the magnetic properties of magnetite crystals produced by MTB is of fundamental interest in fields of geosciences, biomineralization, fine particle magnetism, and planetary sciences. The database of bulk magnetic measurements on MTB is, however, still too sparse to allow for generalizations due to difficulties in obtaining bacteria cells in sufficient quantities from natural environments, and the fact that only a few cell cultures are available. Collaborating with the Munich group, we have carried out the first series of magnetic measurements on air-dried bulk samples containing solely MTB (cocci and M. bavaricum), which were directly isolated from lake sediments, see Figs.1 and 2 below. Oxidation on  magnetosomes are being investigated. We are also studying the cultured MTB (M. gryphiswaldense) and their isolated magnetosomes.
　

Fig 1. FORC diagram of MTB sample (A) and single-domain magnetite powder
sample (B), both derived with a smoothing factor of 2.

　

Fig 2. Comparisons of the air-dried MTB (cross, this study) with
other biogenic magnetite and inorganic magnetite.

     2. The effects of magnetic field on animals and plants

A diverse array of animals, such as homing pigeons, some turtles, spiny lobsters and electric eels, can use the magnetic field of the earth as a cue for spatial orientation. Now scientists postulated biogenic magnetite particles which are commonly found in animals as a common basis for magnetoreception. For example, clusters of SPM nanocrystals were found inside nerve terminals of sensory nerves (ramus ophthalmicus medialis) in the skin inside the upper beak of homing pigeons. The magnetite-loaded terminals in the upper beak are endings of the median ophthalmic nerve (ramus ophthalmicus medialis), and the terminals are sensory endings of the axons positively tested as magnetosensitive. Our current research focuses on the effects of magnetic field on animals (pigeons and bats) and the pathways of acquiring and processing geomagnetic information in animals.

Numerous experiments with seedlings of different plant species placed in weak magnetic field have shown that the growth of their primary roots is inhibited during early germination stages in comparison with control. The proliferative activity and cell reproduction in meristem of plant roots are reduced in weak magnetic field. In our lab, we compare Arabidopsis which grow in magnetic shielded room (2*3*2 m) with which grow in normal earth magnetic field.

　

      



Fig 3. Pigeon and Arabidopsis in our lab

          More will be done in bat ...

   3. Observations of magnetosome growth and chain arrangement of Magnetospirillum magneticum AMB-1

       The formation process and magnetic properties of magnetosomes are of great interest in many relevant fields. We systematically investigated the magnetosome formation in     Magnetospirillum magneticum AMB-1 during batch culture of the cells using both rock magnetic and transmission electron microscopy (TEM) approaches. Here, we report the temporal variations of magnetosome number, grain size and bulk magnetic properties, which indicate a gradual increase in grain size and decrease in non-stoichiometry and/or a better magnetocrystallization of magnetite during magnetosome formation. In addition, under the used growth conditions, AMB-1 formed a fragmental chain of magnetosomes, which includes 3-5 sub-chains aligned along the long axis of the cell. However, strong intra-sub-chain interactions cause each sub-chain to act as an “ideal Stoner-Wohlfarth” particle, and the Moskowitz test is proved to be still valid for the magnetosome subchains. Thus, the presumed “magnetosome sub-chain” pattern is highlighted in this presentation. These findings provide new insights into the magnetosome biomineralization and contribute to better understanding of magnetism of magnetofossils in natural environments.

  4. Diversity of magnetotactic bacteria in the Miyun Lake, China

Fig 4. Different MTBs discovered in Miyun Lake

  5. The biologically controlled mineralization of Ferritin and biologically induced mineralization of some anaerobic bacterials 

  6. Meteorite magnetism