Researchers have long studied magnetotactic bacteria (MTB), aquatic microbes that have the ability to orientate themselves to magnetic fields. This unusual behaviour makes them a subject of interest for improving our understanding of biomagnetism, and potentially harnessing their abilities for future technologies, such as medical nanorobots. Neutrons have been used to explore the characteristics of this magnetism by probing the specialised parts of the cells that are involved.

MTBs exert their magnetic navigation skills using magnetosomes – membrane structures containing magnetic nanoparticles that the bacteria mineralise from their environment. The magnetosomes arrange in a chain that acts like a magnetic compass, allowing the bacteria to move toward the riverbeds they inhabit, using the Earth’s magnetic fields. These unusual nanoparticles have been examined with neutron beams to discover the underlying mechanisms that determine the arrangement and geometry of the chains.

An international collaboration of researchers from University of the Basque Countries, University of Cantabria and the Institut Laue Langevin (ILL) have elucidated the precise structural configuration of the magnetosomes in the MTB strain Magnetospirillum gryphiswaldense. They carried out small-angle neutron scattering (SANS) on a colloid of MTB, a technique that allows them to see the magnetic microstructure of the organisms in detail in aqueous solution. The D33 instrument was employed because of its polarised neutron beam mode, which allowed the researchers to analyse both the structural components and magnetic arrangement – possible because neutrons will interact with both. Magnetic nanoparticles are central to many applications, ranging from biomedical diagnostics to data storage, and even hyperthermia cancer treatments, but the magnetic structures within and in between nanoparticles are challenging to probe directly. Neutron-spin resolved small-angle neutron scattering is one of the few tools that can be used to investigate nanoparticles.
Using SANS, the researchers have gained new insight into the structure of the magnetosome chain.