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
- BESSY II: High-resolution insights into individual biomolecules and catalystsVery small biological samples and even individual biomolecules can now be examined under near-physiological conditions with high confidence at the BESSY II infrared beamline with a newly validated and improved technique: The nanoscale infrared spectroscopy (s-SNOM) with ultra-thin silicon-based membranes. An international team demonstrated after an initial proof of concept, that high-resolution (a few tens of nanometres) nano-IR measurements reliably match expected far-field IR spectra in an aqueous environment. This methodological advance provides a solid foundation for studying biomaterials or observing catalytic processes in a liquid environment.
- New method shows how molecular switches are influenced by their neighborsResearchers at Friedrich Schiller University Jena and the Helmholtz Centre Berlin (HZB) have, for the first time, been able to directly observe how the environment surrounding a molecular switch influences its electronic structure. Molecular switches are molecules that can be switched between two states by external influences such as changes in temperature—similar to a switch with the positions »On« and »Off«. Such molecules are being investigated as potential building blocks for future data storage devices or sensor materials. Using magnetic-field-dependent terahertz spectroscopy, the researchers have now, for the first time, been able to distinguish whether neighbouring molecules in a material are in the same or different states. The results have been published in the journal »Angewandte Chemie International Edition«.
- BESSY II is back in operation after maintenance shutdownOn 7 September 2026, BESSY II was set into operation after a four-week shutdown. BESSY II is scheduled to resume full user operation on 22 September.