Magnetotactic bacteria (MTB) produce highly organized chains of magnetite nanoparticles within intracellular membranes called magnetosomes. The alignment of these magnetic nanoparticles endows the bacteria with a substantial magnetic dipole, which it can use in relation to the earth’s magnetic field to navigate its environment. Magnetite nanoparticles of consistent size, composition and shape are produced by MTB through a highly controlled biomineralization process. The resultant size and morphology of magnetite nanoparticles provide optimal magnetic properties for a wide-range of biomedical applications from drug delivery to hyperthermia therapy. For these reasons, magnetite biomineralization from MTB has been of interest for several years as scientists try to understand the chemical mechanism behind the highly efficient production of magnetite nanoparticles. Harnessing or adopting chemical pathways similar to the bacteria should benefit the production and utility of magnetite nanoparticles for technological advancements in areas such as medical imaging, diagnostics, drug delivery systems, industrial catalysts and magnetic data storage.
This project aimed to capture and understand the formation and properties of magnetite nanoparticles within living MTB. Previous studies have utilized ex situ methods where sample extraction and preparation for measurements could produce artefacts or disturb the original state of the biomineralization process. To accomplish this objective, a microfluidic device was constructed to host and accommodate the growth environment conditions for MTB and to enable in situ measurement using a combination of X-ray spectroscopy and X-ray microscopy. The microfluidic device limited the liquid layer to a few micrometers and immobilized a single layer of MTB on the substrate. There are further optimizations to be made, but progress has demonstrated the potential to collect X-ray fluorescence image of a single bacterium. On the biomineralization mechanism, an ex situ study was conducted using X-ray fluorescence microscopy to assess the iron composition at varied stages of biomineralization on a single-cell level. This was achieved by performing X-ray absorption spectroscopy mapping over a single cell region and applying statistical methods to interpret the composition of iron species present. By changing the iron concentration experienced by the bacteria and the magnetosome formation induction mechanism, the work conducted sheds light on how these bacteria are able to store iron intracellularly outside of magnetosomes during the biomineralization process. This will have implications on the formation mechanism that has been postulated from previous studies and on the iron biogeochemical cycle in the environment.
