Generation of nanomagnetic biocomposites by genetic engineering of bacterial magnetosomes

Abstract

Magnetosomes are magnetic nanoparticles biomineralized by magnetotactic bacteria. They consist of a monocrystalline magnetite core enveloped by the magnetosome membrane, which harbors a set of specialized proteins. For the alphaproteobacterium Magnetospirillum gryphiswaldense genetic techniques were developed for engineering both crystal morphology and the enveloping membrane, thereby generating building blocks for magnetic organic–inorganic hybrid materials. Genetic manipulation of magnetite biomineralization enabled the generation of core-engineered nanoparticles with adjusted magnetic and physicochemical properties. Functionalization of the particle surface was achieved by genetic expression of enzymes and peptides genetically fused to abundant magnetosome anchor proteins. High-level expression allowed the generation of multifunctional nanoparticles with maximized protein-to-particle ratios. This allowed for the tuning of surface properties (charge and hydrodynamic diameter), and the colloidal and enzymatic stability was improved by coating with inorganic and organic shells. The expression of molecular connectors might serve as scaffolds for the introduction of further functionalities. Overall, this demonstrates that the ‘synthetic biology’ approach enables the generation of multifunctional, magnetic hybrid materials with a tuned property spectrum exceeding those of conventional materials, and the combination of different biogenic materials generates fully genetically encoded biocomposites with enhanced potential for various biotechnological and biomedical applications.

Probing the Nanostructure and Arrangement of Bacterial Magnetosomes by Small-Angle X-Ray Scattering

“…One magnetosome consists of a magnetite crystal, surrounded by a proteinaceous membrane (Fig. 2a), which exerts strict control over the growth of the crystals and their arrangement into well-ordered chains (4, 12). Based on previous TEM imaging of magnetosome chains within M. gryphiswaldense (24, 25), magnetosome biogenesis is here considered as the formation of a single linear chain composed of individual core shell particles, which exhibit sharp phase boundaries and are closely packed (Fig.…”

“…This is partially due to a lack of practical lab-scale methods to assess bulk magnetosome formation in growing cells. In addition, magnetosomes are of increasing interest as biogenic magnetic nanoparticles, as they have already been successfully explored in a wide range of potential biotechnical and biomedical applications, including in magnetic hyperthermia (7, 8), as contrast agents (9, 10), or in particle-based immunoassays (11–13). Yet, bioproduction of magnetosome particles depends on highly controlled growth conditions (14, 15) and requires precise and permanent monitoring of bulk magnetosome biomineralization during bacterial cultivation.…”

“…This technique represents a volume-averaging method to study nanoscale interfaces based on electron density heterogeneities within a sample. SAXS experiments performed on a laboratory-based setup provide access to size, shape, and orientation of nanoscale objects spanning a size range of 1 to 300 nm and are thus ideally suited to study structural parameters and aggregation behavior of intermediates and final products formed during magnetosome biomineralization, as the mature nanoparticles exhibit an average size of about 40 nm (4, 12) and a substantial electron density contrast. During magnetosome biogenesis, the forming particles characteristically undergo a morphological transition leading to changes in the electron density distribution at different growth stages.…”

Bacterial Magnetosomes as Novel Platform for the Presentation of Immunostimulatory, Membrane‐Bound Ligands in Cellular Biotechnology

“…Furthermore, magnetosomes can be genetically engineered by expression of foreign proteins as fusions to highly abundant magnetosome membrane (Mam) proteins. Using this approach, the feasibility to express antibodies, fluorophores, enzymes and receptors was already demonstrated 9,10. In addition to stable protein display, it can be assumed that the oligomerization of monomeric subunits into functional multimeric structures is facilitated, as recently has been shown for enzymes like the glucuronidase GusA or glucose oxidase 11,12.…”

Genetic Tuning of Iron Oxide Nanoparticle Size, Shape, and Surface Properties in Magnetospirillum magneticum

“…[ 30 ] The magnetosome lipid coating can be preserved and embedded with proteins to functionalize the IONPs. [ 21,35–37 ] Purified magnetosomes can be chemically modified, for instance, by encapsulation with a silica shell. [ 27 ] Isolated magnetosome nanoparticles exhibit low biotoxicity [ 38 ] and are promising candidates for biomedical applications.…”