Sarah S. Staniland

Rapid magnetosome formation shown by real-time x-ray magnetic circular dichroism.

Magnetosomes are magnetite nanoparticles formed by biomineralization within magnetotactic bacteria. Although there have been numerous genetic and proteomic studies of the magnetosome-formation process, there have been only limited and inconclusive studies of mineral-phase evolution during the formation process, and no real-time studies of such processes have yet been performed. Thus, suggested formation mechanisms still need substantiating with data. Here we report the examination of the magnetosome material throughout the formation process in a real-time in vivo study of Magnetospirillum gryphiswaldense, strain MSR-1. Transmission EM and x-ray absorption spectroscopy studies reveal that full-sized magnetosomes are seen 15 min after formation is initiated. These immature magnetosomes contain a surface layer of the nonmagnetic iron oxide-phase hematite. Mature magnetite is found after another 15 min, concurrent with a dramatic increase in magnetization. This rapid formation result is contrary to previously reported studies and discounts the previously proposed slow, multistep formation mechanisms. Thus, we conclude that the biomineralization of magnetite occurs rapidly in magnetotactic bacteria on a similar time scale to high-temperature chemical precipitation reactions, and we suggest that this finding is caused by a biological catalysis of the process.

Biotemplated magnetic nanoparticle arrays

Immobilized biomineralizing protein Mms6 templates the formation of uniform magnetite nanoparticles in situ when selectively patterned onto a surface. Magnetic force microscopy shows that the stable magnetite particles maintain their magnetic orientation at room temperature, and may be exchange coupled. This precision-mixed biomimetic/soft-lithography methodology offers great potential for the future of nanodevice fabrication.

Magnetic bacterial protein Mms6 controls morphology, crystallinity and magnetism of cobalt-doped magnetite nanoparticles in vitro

Magnetic nanoparticles (MNPs) are in high demand within biomedical and nanotechnological industries. Size, shape, material and crystal quality directly affect the particles properties, namely their magnetic characteristics, and must be tuned and controlled to meet the specification of the application. A key challenge is to refine synthetic methods to tailor the MNP properties with precision, but using cheap, high-yield, industrially robust and environmentally friendly methods. In this study we compare simple high-yield precipitation methods of producing cobalt-doped magnetite MNPs. We explore the variation of magnetic coercivity and saturation with increasing Co-doping from 0–15% in magnetite MNPs, which increases coercivity from 5–62 mT, but decreases saturation from 91–28 emu g−1. An optimum of 6% was further investigated as this produced the greatest increase in coercivity to 34 mT with a relatively small reduction in saturation magnetisation to 79 emu g−1. The methods compared are refined with the addition of the recombinant biomineralisation protein Mms6 from a magnetic bacterium, as this has been shown to help control magnetite MNP morphology and grainsize distribution in vitro. Similar control is seen here over our Co-doped magnetite synthesis. Mms6 increases the size and decreases the size distribution of room temperature co-precipitated particles from 11.7 nm to 31.7 nm. The affinity tagged protein his6Mms6 also controls the size (23.2 nm) but less effectively than Mms6. Therefore the Mms6 mediated Co-doped MNP particles are found to be single domain and thus give very clear, square magnetic hysteresis with a coercivity of 48 mT at 10 K. Hysteresis of the smaller particles (Co-doped MNP with no protein and with his-tagged protein) clearly shows both superparamagnetic and single-domain magnetic behaviours. Powder X-ray diffraction shows that both the addition of Mms6 and cobalt increases the crystal quality of the MNP. Thus Mms6 protein mediated room temperature co-precipitation offers an environmentally friendly, industrially robust route towards tailored, uniform, single-domain, high-quality Co-doped magnetite MNPs.

Protein and peptide biotemplated metal and metal oxide nanoparticles and their patterning onto surfaces

Metal and metal oxide nanoparticles (NPs) have many uses, and the size, shape and purity of the NPs must be uniform to ensure that the particles function in a known and consistent manner. The synthesis of uniform NPs usually requires high temperatures, high pressures, and harsh chemical reagents, which is both economically and environmentally costly. In nature, biomineralisation is used to produce precise, pure NPs, using far milder reaction conditions and reagents. Recently, a bioinspired approach has been adopted to produce NPs using proteins and peptides that: occur in nature; are artificially selected from a random peptide library by biopanning; or are rationally designed to control NP formation under mild conditions. Here we highlight the recent advances in metal and metal oxide NP binding and synthesis using proteins and peptides. We then investigate bioinspired patterning of NPs onto surfaces. This is done to demonstrate the possible avenues available to develop environmentally friendly, biotemplated devices and nanotechnologies in the future.

Simultaneously discrete biomineralization of magnetite and tellurium nanocrystals in magnetotactic bacteria.

ABSTRACT Magnetotactic bacteria synthesize intracellular magnetosomes comprising membrane-enveloped magnetite crystals within the cell which can be manipulated by a magnetic field. Here, we report the first example of tellurium uptake and crystallization within a magnetotactic bacterial strain, Magnetospirillum magneticum AMB-1. These bacteria independently crystallize tellurium and magnetite within the cell. This is also highly significant as tellurite (TeO32−), an oxyanion of tellurium, is harmful to both prokaryotes and eukaryotes. Additionally, due to its increasing use in high-technology products, tellurium is very precious and commercially desirable. The use of microorganisms to recover such molecules from polluted water has been considered as a promising bioremediation technique. However, cell recovery is a bottleneck in the development of this approach. Recently, using the magnetic property of magnetotactic bacteria and a cell surface modification technology, the magnetic recovery of Cd2+ adsorbed onto the cell surface was reported. Crystallization within the cell enables approximately 70 times more bioaccumulation of the pollutant per cell than cell surface adsorption, while utilizing successful recovery with a magnetic field. This fascinating dual crystallization of magnetite and tellurium by magnetotactic bacteria presents an ideal system for both bioremediation and magnetic recovery of tellurite.

Innovation through imitation: biomimetic, bioinspired and biokleptic research

While biomimetic research is becoming increasingly popular the term is being used for a broader range of research and it is becoming more difficult for researchers to understand and define. In this opinion article we discuss how biomimetic research overlaps with and differs from the complementary fields of biotechnology, biokleptic and bioinspired research as we attempt to describe each area with definitions, examples and discussion. What makes research biomimetic, bioinspired or biokleptic is put under scrutiny as we ask: can different components, parts and processes of an experiment be categorised separately? What is the difference between a biological and synthetic system/component? Is the scientist or biology in control? The answers to which aim to untangle the subtleties of the biomimetics field.

Self-assembled MmsF proteinosomes control magnetite nanoparticle formation in vitro

Significance Magnetotactic bacteria produce morphologically precise magnetite nanoparticles within organelles termed “magnetosomes.” Biomineralization proteins tightly regulate crystallization of these nanoparticles. A master protein regulator of particle morphology in vivo, magnetosome membrane specific F (MmsF), has recently been discovered. In this study, we purified MmsF and two homologous proteins from Magnetospirillum magneticum strain AMB-1. MmsF imposes strict control over the formation of magnetite nanoparticles when added to chemical precipitation reactions, whereas the highly similar homologues produce alternative iron oxides with less desirable magnetic properties. Remarkably, these intrinsic membrane proteins with three membrane-spanning regions are water-soluble and self-assemble in vitro into nanoscale “proteinosomes.” We speculate that self-assembly exists in vivo and might be required for the activity of the protein. Magnetotactic bacteria synthesize highly uniform intracellular magnetite nanoparticles through the action of several key biomineralization proteins. These proteins are present in a unique lipid-bound organelle (the magnetosome) that functions as a nanosized reactor in which the particle is formed. A master regulator protein of nanoparticle formation, magnetosome membrane specific F (MmsF), was recently discovered. This predicted integral membrane protein is essential for controlling the monodispersity of the nanoparticles in Magnetospirillum magneticum strain AMB-1. Two MmsF homologs sharing over 60% sequence identity, but showing no apparent impact on particle formation, were also identified in the same organism. We have cloned, expressed, and used these three purified proteins as additives in synthetic magnetite precipitation reactions. Remarkably, these predominantly α-helical membrane spanning proteins are unusually highly stable and water-soluble because they self-assemble into spherical aggregates with an average diameter of 36 nm. The MmsF assembly appears to be responsible for a profound level of control over particle size and iron oxide (magnetite) homogeneity in chemical precipitation reactions, consistent with its indicated role in vivo. The assemblies of its two homologous proteins produce imprecise various iron oxide materials, which is a striking difference for proteins that are so similar to MmsF both in sequence and hierarchical structure. These findings show MmsF is a significant, previously undiscovered, protein additive for precision magnetite nanoparticle production. Furthermore, the self-assembly of these proteins into discrete, soluble, and functional “proteinosome” structures could lead to advances in fields ranging from membrane protein production to drug delivery applications.

Nanomagnetic Arrays Formed with the Biomineralization Protein Mms6

Many Modern Technologies, such as High Density Data Storage, Require Monodispersed Magnetic Nanoparticles (MNPs), which Have a Consistent Magnetic Behavior, Specifically Immobilized onto a Patterned Surface. Current Methods for Synthesizing Uniform Mnps Require High Temperatures and Harsh Chemicals, which Is Not Environmentally Friendly. Also, the Particles Are Expensive to Make and Expensive to Pattern Using Conventional Lithography Methods. Magnetic Bacteria Are Able to Synthesize Consistent Mnps in Vivo Using Biomineralization Proteins inside Magnetosome Vesicles to Control Particle Size and Shape and Make Single Domain Mnps. Mms6 Is a Biomineralization Protein that Is Able to Template Cubo-Octahedral MNP Formation in Vitro. it Is Thought the N-Terminus Helps Integrate the Protein into the Magnetosome Membrane, and the C-Terminus Interacts with Magnetite during Nucleation and/or MNP Growth. by Selectively Attaching Mms6 to a Patterned Self Assembled Monolayer via the N-Terminus, Patterns of Uniform Magnetite Mnps Are Templated in Situ. this Also Requires Careful Selection of the Mineralization Solution Used to Mineralize the Patterned Mms6. here we Evaluate some Low Temperature (room Temperature to < 100°C) Methods of Magnetite Formation to Produce Monodispersed Magnetite Mnps onto Immobilized Mms6. Room Temperature Co-Precipitation (RTCP) Was Found to Be Unsuitable, as the Magnetite Does Not Form on the Immobilized Mms6, but Appears to Form Rapidly as Base Is Added. Partial Oxidation of Ferrous Hydroxide (POFH) Was Found to Be Able to Form Consistent Magnetite Mnps on the Immobilized Mms6, as the Reactants Gradually Mature to Form Magnetite over a few Hours (at 80°C) or a few Days (room Temperature). by Carefully Controlling the Type of Base Used, the Ratio of the Reactants and the Temperature and Duration of the POFH Mineralization Reaction, this System Was Optimized to Produce Consistent Mnps (340 ± 54 Nm, Coercivity 109 Oe) on the Immobilized Mms6, with Scarcely any Mineralization on the Anti-Biofouling Background. the Mnps Are Ferrimagnetic, and Appear to Be Exchange Coupled across Multiple Particles in MFM Measurements. the Specificity of this Method towards Precise Magnetite Mineralization under Relatively Mild Conditions May Be Adapted to Nanoscale Patterning of Multiple Biotemplated Materials, by Using other Biomineralization Proteins or Peptides. this Would Allow the Fabrication of Cheaper, More Environmentally Friendly Components for Devices of the Future.

Biomimetic Synthesis of Materials for Technology

In a world with ever decreasing natural reserves, researchers are striving to find sustainable methods of producing components for technology. Bioinspired, biokleptic and biomimetic materials can be used to form a wide range of technologically relevant materials under environmentally friendly conditions. Here we investigate a range of biotemplated and bioinspired materials that can be used to develop components for devices, such as optics, photonics, photovoltaics, circuits and data storage.

Cell division in magnetotactic bacteria splits magnetosome chain in half

Cell division in magnetotactic bacteria has attracted much interest, speculation and hypothesis with respect to the biomineralised chains of magnetic iron‐oxide particles known as magnetosomes. Here we report direct Transmission Electron Microscopy (TEM) evidence that division occurs at a central point of the cell and the chain, cleaving the magnetosome chain in two. Additionally, the new magnetosome chain relocates rapidly to the centre of the daughter cell and the number of magnetosomes is directly proportional to the cell length, even during the division part of the cell cycle. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)