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
- Battery research with the HZB X-ray microscopeNew cathode materials are being developed to further increase the capacity of lithium batteries. Multilayer lithium-rich transition metal oxides (LRTMOs) offer particularly high energy density. However, their capacity decreases with each charging cycle due to structural and chemical changes. Using X-ray methods at BESSY II, teams from several Chinese research institutions have now investigated these changes for the first time with highest precision: at the unique X-ray microscope, they were able to observe morphological and structural developments on the nanometre scale and also clarify chemical changes.
- BESSY II: New procedure for better thermoplasticsBio-based thermoplastics are produced from renewable organic materials and can be recycled after use. Their resilience can be improved by blending bio-based thermoplastics with other thermoplastics. However, the interface between the materials in these blends sometimes requires enhancement to achieve optimal properties. A team from the Eindhoven University of Technology in the Netherlands has now investigated at BESSY II how a new process enables thermoplastic blends with a high interfacial strength to be made from two base materials: Images taken at the new nano station of the IRIS beamline showed that nanocrystalline layers form during the process, which increase material performance.
- Hydrogen: Breakthrough in alkaline membrane electrolysersA team from the Technical University of Berlin, HZB, IMTEK (University of Freiburg) and Siemens Energy has developed a highly efficient alkaline membrane electrolyser that approaches the performance of established PEM electrolysers. What makes this achievement remarkable is the use of inexpensive nickel compounds for the anode catalyst, replacing costly and rare iridium. At BESSY II, the team was able to elucidate the catalytic processes in detail using operando measurements, and a theory team (USA, Singapore) provided a consistent molecular description. In Freiburg, prototype cells were built using a new coating process and tested in operation. The results have been published in the prestigious journal Nature Catalysis.