Magnetite Biomineralization in Magnetospirillum gryphiswaldense: Time-Resolved Magnetic and Structural Studies

Abstract

Magnetotactic bacteria biosynthesize magnetite nanoparticles of high structural and chemical purity that allow them to orientate in the geomagnetic field. In this work we have followed the process of biomineralization of these magnetite nanoparticles. We have performed a time-resolved study on magnetotactic bacteria Magnetospirillum gryphiswaldense strain MSR-1. From the combination of magnetic and structural studies by means of Fe K-edge X-ray absorption near edge structure (XANES) and high-resolution transmission electron microscopy we have identified and quantified two phases of Fe (ferrihydrite and magnetite) involved in the biomineralization process, confirming the role of ferrihydrite as the source of Fe ions for magnetite biomineralization in M. gryphiswaldense. We have distinguished two steps in the biomineralization process: the first, in which Fe is accumulated in the form of ferrihydrite, and the second, in which the magnetite is rapidly biomineralized from ferrihydrite. Finally, the XANES analysis suggests that the origin of the ferrihydrite could be at bacterial ferritin cores, characterized by a poorly crystalline structure and high phosphorus content.

Genetic Dissection of the mamAB and mms6 Operons Reveals a Gene Set Essential for Magnetosome Biogenesis in Magnetospirillum gryphiswaldense

“…In contrast, excision of mamI in M. gryphiswaldense did not entirely abolish the biomineralization of electron-dense iron-rich particles, but the mutant still synthesized tiny and poorly crystalline nonmagnetic particles, which in some cases were shown to consist of hematite. Recent findings for M. gryphiswaldense and M. magneticum indicate that the observed poorly ordered iron (oxyhydr)oxide phases are precursors to the magnetite phase in bacteria (41,52). In addition, the ability of MamP to precipitate ferrihydrite and magnetite in vitro suggests that magnetite may be formed through a stepwise phase transformation process (48).…”

Magnetotactic bacteria form magnetite from a phosphate-rich ferric hydroxide via nanometric ferric (oxyhydr)oxide intermediates

“…On the basis of X-ray circular magnetic dichroism, hematite (α-Fe 2 O 3 ) was found as a precursor to magnetite in the same bacterial strain and was suggested to represent an outer layer around the nascent magnetite phase from which it grew (21). Very recently, the involvement of bacterioferritin in the mineralization pathway was again suggested in this strain (22). Thus, it remained to be determined which of the differently proposed precursor materials is involved in the mineralization of magnetite or how the different findings can be reconciled, how the precursors are spatially distributed within the bacterial cell, and how the phase transformation proceeds from precursor to final mineral.…”

Effect of Surface Hydrophobicity on the Function of the Immobilized Biomineralization Protein Mms6

“…12,13 Although magnetotactic bacteria were discovered almost four decades ago, little is known about the mechanisms by which bacteria synthesize these magnetic crystals. 9,11,14 Recently, with the discovery and isolation of new bacterial strains and the development of new techniques, there has been progress in understanding magnetosome formation. 9,15,16 Inspired by nature, the chemical synthesis of hybrid materials with unusual morphologies at several length scales has received considerable interest from the research community.…”