Controlled cobalt doping in the spinel structure of magnetosome magnetite: new evidences from element- and site-specific X-ray magnetic circular dichroism analyses

Abstract

ResearchCite this article: Li J et al. 2016 Controlled cobalt doping in the spinel structure of magnetosome magnetite: new evidences from element-and site-specific X-ray magnetic circular dichroism analyses. J. R. Soc. The biomineralization of magnetite nanocrystals (called magnetosomes) by magnetotactic bacteria (MTB) has attracted intense interest in biology, geology and materials science due to the precise morphology of the particles, the chain-like assembly and their unique magnetic properties. Great efforts have been recently made in producing transition metal-doped magnetosomes with modified magnetic properties for a range of applications. Despite some successful outcomes, the coordination chemistry and magnetism of such metal-doped magnetosomes still remain largely unknown. Here, we present new evidences from X-ray magnetic circular dichroism (XMCD) for element-and site-specific magnetic analyses that cobalt is incorporated in the spinel structure of the magnetosomes within Magnetospirillum magneticum AMB-1 through the replacement of Fe 2þ ions by Co 2þ ions in octahedral (O h ) sites of magnetite. Both XMCD at Fe and Co L 2,3 edges, and energy-dispersive X-ray spectroscopy on transmission electron microscopy analyses reveal a heterogeneous distribution of cobalt occurring either in different particles or inside individual particles. Compared with nondoped one, cobalt-doped magnetosome sample has lower Verwey transition temperature and larger magnetic coercivity, related to the amount of doped cobalt. This study also demonstrates that the addition of trace cobalt in the growth medium can significantly improve both the cell growth and the magnetosome formation within M. magneticum AMB-1. Together with the cobalt occupancy within the spinel structure of magnetosomes, this study indicates that MTB may provide a promising biomimetic system for producing chains of metal-doped single-domain magnetite with an appropriate tuning of the magnetic properties for technological and biomedical applications.

Magnetosomes could be protective shields against metal stress in magnetotactic bacteria

“…Note that, according to EDS (see the supplementary information), the Co content in the magnetosomes is only 1.6% at./Fe, thus the Co ferrite in the magnetosomes is not stoichiometric ( Co 0.05 Fe 2.95 O 4 ). In spite of the low Co content, it has been previously reported that the magnetic properties of Co-magnetosomes change notably with respect to the undoped ones [20][21][22] .…”

“…Note that, according to EDS (see the supplementary information), the Co content in the magnetosomes is only 1.6% at./Fe, thus the Co ferrite in the magnetosomes is not stoichiometric ( ). In spite of the low Co content, it has been previously reported that the magnetic properties of Co-magnetosomes change notably with respect to the undoped ones 20 – 22 . Mn The control bacteria show a well defined Mn K-edge XANES spectrum, suggesting that Mn is an abundant element in the cell in basal conditions (Fig.…”

A Method for Producing Highly Pure Magnetosomes in Large Quantity for Medical Applications Using Magnetospirillum gryphiswaldense MSR-1 Magnetotactic Bacteria Amplified in Minimal Growth Media

“…We have also studied the impact of minimal growth media on magnetosome composition. Whereas, we increased magnetosome iron relative purity by reducing the concentration of other metals than iron in the growth media, i.e., the concentration of iron relatively to other analyzed metals in magnetosomes increases from 93.8% using non-minimal growth media (Zhang et al, 2011) to 99.8% using minimal growth media, previous studies have reported a faculty of MTB to incorporate other metals than iron, such as Co, Zn or Ni, in magnetosomes by growing MTB in media enriched with these metals (Staniland et al, 2008;Kundu et al, 2009;Li et al, 2016). Another interesting observation lies in the rate of metal incorporation, which seems to depend on the type of metal that is considered.…”

“…This task was not won in advance. Indeed, some of the metals that we needed to eliminate like cobalt have been reported to be necessary for biosynthesis of the B12 vitamin and in some key enzymes responsible for magnetosome formation in AMB-1 strain (Li et al, 2016). Furthermore, according to previous reports, other metals like copper, manganese and zinc, could be essential since they are agents acting as cofactors of bacterial antioxidant defense enzymes (Agranoff and Sanjeev, 1998), thus preventing oxidative stress in bacteria and modifying magnetosomes characteristics (Popa and Fang, 2009).…”

Formation of Core-Shell Nanoparticles Composed of Magnetite and Samarium Oxide in Magnetospirillum magneticum Strain RSS-1

“…It is supposed that transition metal ions doped in magnetosomes are in the +2 oxidation state and occupy some Fe 2+ octahedral sites in the Fe 3 O 4 inverse spinel structure. It was in fact recently clarified that Fe 2+ ions were replaced by Co 2+ at the octahedral sites of magnetosome magnetite [ 16 ]. It was also demonstrated that Magnetospirillum species incorporate copper and manganese into magnetosomes, as a result of which the magnetic properties of magnetite particles alter [ 17 , 18 ].…”