BESSY II sheds light on how the internal compass is constructed in magnetotactic bacteria
The magnetosomes form a chain inside the bacteria's cell shows the electron cryotomography (ECT). © 10.1039/C7NR08493E
Experiments at BESSY II revealed how an external magnetic field changes the orientiations of chain parts. © 10.1039/C7NR08493E
Bacteria exist in many shapes and with very different talents. Magnetotactic bacteria can even sense the earth’s magnetic field by making use of magnetic nanoparticles in their interior that act as an internal compass. Spanish teams and experts at Helmholtz-Zentrum Berlin have now examined the magnetic compass of Magnetospirillum gryphiswaldense at BESSY II. Their results may be helpful in designing actuation devices for nanorobots and nanosensors for biomedical applications.
Magnetotactic bacteria are usually found in freshwater and marine sediments. One species, Magnetospirillum gryphiswaldense, is easily cultivated in the lab – with or without magnetic nanoparticles in their interior depending on the presence or absence of iron in the local environment. “So these microorganisms are ideal test cases for understanding how their internal compass is constructed”, explains Lourdes Marcano, a PhD student in physics at Universidad del Pais Vasco in Leioa, Spain.
Chain of magnetic nanoparticles form compass
Magnetospirillum cells contain a number of small particles of magnetite (Fe3O4), each approx. 45 nanometers wide. These nanoparticles, called magnetosomes, are usually arranged as a chain inside the bacteria. This chain acts as a permanent dipole magnet and is able to passively reorient the whole bacteria along the Earth’s magnetic field lines. “The bacteria exist preferentially at the oxy/anoxy transition zones”, Marcano points out, “and the internal compass might help them to find the best level in the stratified water column for satisfying their nutritional requirements.” The Spanish scientists examined the shape of the magnetosomes and their arrangement inside the cells using various experimental methods such as electron cryotomography.
Isolated chains examined at BESSY II
Samples of isolated magnetosome chains were analysed at BESSY II to investigate the relative orientation between the chain’s direction and the magnetic field generated by the magnetosomes. “Current methods employed to characterise the magnetic properties of these bacteria require sampling over hundreds of non-aligned magnetosome chains. Using photoelectron emission microscopy (PEEM) and X-ray magnetic circular dichroism (XMCD) at HZB, we are able to “see” and characterise the magnetic properties of individual chains”, explains Dr. Sergio Valencia, HZB. “Being able to visualise the magnetic properties of individual magnetosome chains opens up the possibility of comparing the results with theoretical predictions.”
Helical shape
Indeed, the experiments revealed that the magnetic field orientation of the magnetosomes is not directed along the chain direction, as assumed up to now, but is slightly tilted. As the theoretical modelling of the Spanish group suggests, this tilt might explain why magnetosome chains are not straight but helical in shape.
Outlook: Nature as a model
A deeper understanding of the mechanisms determining the chain shape is very important, the scientists point out. Nature’s inventions could inspire new biomedical solutions such as nanorobots propelled by flagella systems in the direction provided by their magnetosome chain.
Publication in Nanoscale (2018): “Configuration of the magnetosome chain: a natural magnetic nanoarchitecture”; I. Orue, L. Marcano, P. Bender, A. Garcıa-Prieto, S. Valencia, M.A. Mawass, D. Gil-Carton, D. Alba Venero, D. Honecker, A. Garcıa-Arribas, L. Fernandez Barquın, A. Muela, M.L. Fdez-Gubieda
DOI: 10.1039/C7NR08493E
- Iridium-free catalysts for acid water electrolysis investigatedHydrogen will play an important role, both as a fuel and as a raw material for industry. However, in order to produce relevant quantities of hydrogen, water electrolysis must become feasible on a multi-gigawatt scale. One bottleneck is the catalysts required, with iridium in particular being an extremely rare element. An international collaboration has therefore investigated iridium-free catalysts for acidic water electrolysis based on the element cobalt. Through investigations with various methods, among them experiments at the LiXEdrom at the BESSY II X-ray source in Berlin, they were able to elucidate processes that take place during water electrolysis in a cobalt-iron-lead oxide material as the anode. The study is published in Nature Energy.
- Self assembling monolayer can improve lead-free perovskite solar cells tooTin perovskite solar cells are not only non-toxic, but also potentially more stable than lead-containing perovskite solar cells. However, they are also significantly less efficient. Now, an international team has succeeded in reducing losses in the lower contact layer of tin perovskite solar cells: The scienstists identified chemical compounds that self-assemble into a molecular layer that fits very well with the lattice structure of tin perovskites. On this monolayer, tin perovskite with excellent optoelectronic quality can be grown, which increases the performance of the solar cell.
- Scrolls from Buddhist shrine virtually unrolled at BESSY IIThe Mongolian collection of the Ethnological Museum of the National Museums in Berlin contains a unique Gungervaa shrine. Among the objects found inside were three tiny scrolls, wrapped in silk. Using 3D X-ray tomography, a team at HZB was able to create a digital copy of one of the scrolls. With a mathematical method the scroll could be virtually unrolled to reveal the scripture on the strip. This method is also used in battery research.