Crystallite sizes and lattice parameters of nano-biomagnetite particles.

Average crystallite sizes of microbially synthesized pure, metal-, and lanthanide-substituted magnetite (bio-magnetite) were determined for a variety of incubation times and temperatures, substitutional elements and amounts, bacterial species, and precursor types. The intriguing difference between nanoparticle bio-magnetite and chemically synthesized magnetite (chem-magnetite) was that powder X-ray diffraction (XRD) data showed that the bio-magnetite exhibited slightly smaller lattice parameters, however, Raman Spectroscopy exhibited no difference in Fe-O bonding. These results indicate that bio-magnetite likely exhibits a more compact crystal structure with less uncoordinated iron on the surface suppressing negative pressure effects. The bio-magnetite with decreased lattice parameters could have potential technological advantages over current commercial chemically synthesized magnetites.

Microbial preparation of metal-substituted magnetite nanoparticles.

A microbial process that exploits the ability of iron-reducing microorganisms to produce copious amounts of extra-cellular metal (M)-substituted magnetite nanoparticles using akaganeite and dopants of dissolved form has previously been reported. The objectives of this study were to develop methods for producing M-substituted magnetite nanoparticles with a high rate of metal substitution by biological processes and to identify factors affecting the production of nano-crystals. The thermophilic and psychrotolerant iron-reducing bacteria had the ability to form M-substituted magnetite nano-crystals (M(y)Fe(3-y)O(4)) from a doped precursor, mixed-M iron oxyhydroxide, (M(x)Fe(1-x)OOH, x< or =0.5, M is Mn, Zn, Ni, Co and Cr). Within the range of 0.01< or =x< or =0.3, using the mixed precursor material enabled the microbial synthesis of more heavily substituted magnetite compared to the previous method, in which the precursor was pure akaganeite and the dopants were present as soluble metal salts. The mixed precursor method was especially advantageous in the case of toxic metals such as Cr and Ni. Also this new method increased the production rate and magnetic properties of the product, while improving crystallinity, size control and scalability.

Microbial formation of lanthanide-substituted magnetites by Thermoanaerobacter sp. TOR-39.

The potentially toxic effects of soluble lanthanide (L) ions, although microbially induced mineralization can facilitate the formation of tractable materials, has been one factor preventing the more widespread use of L-ions in biotechnology. Here, we propose a new mixed-L precursor method as compared to the traditional direct addition technique. L (Nd, Gd, Tb, Ho and Er)-substituted magnetites, L( y )Fe(3 - y )O(4) were microbially produced using L-mixed precursors, L( x )Fe(1 - x )OOH, where x = 0.01-0.2. By combining lanthanides into the akaganeite precursor phase, we were able to mitigate some of the toxicity, enabling the microbial formation of L-substituted magnetites using a metal reducing bacterium, Thermoanaerobacter sp. TOR-39. The employment of L-mixed precursors enabled the microbial formation of L-substituted magnetite, nominal composition up to L(0.06)Fe(2.94)O(4), with at least tenfold higher L-concentration than could be obtained when the lanthanides were added as soluble salts. This mixed-precursor method can be used to extend the application of microbially produced L-substituted magnetite, while also mitigating their toxicity.