Formation of magnetite by bacteria and its application

Abstract

Magnetic particles offer high technological potential since they can be conveniently collected with an external magnetic field. Magnetotactic bacteria synthesize bacterial magnetic particles (BacMPs) with well-controlled size and morphology. BacMPs are individually covered with thin organic membrane, which confers high and even dispersion in aqueous solutions compared with artificial magnetites, making them ideal biotechnological materials. Recent molecular studies including genome sequence, mutagenesis, gene expression and proteome analyses indicated a number of genes and proteins which play important roles for BacMP biomineralization. Some of the genes and proteins identified from these studies have allowed us to express functional proteins efficiently onto BacMPs, through genetic engineering, permitting the preservation of the protein activity, leading to a simple preparation of functional protein-magnetic particle complexes. They were applicable to high-sensitivity immunoassay, drug screening and cell separation. Furthermore, fully automated single nucleotide polymorphism discrimination and DNA recovery systems have been developed to use these functionalized BacMPs. The nano-sized fine magnetic particles offer vast potential in new nano-techniques.

Figure 1

TEM images of magnetotactic bacteria. (a) Magnetospirillum magneticum strain AMB-1 and (b) Desulfovibrio magneticus strain RS-1. BacMPs of (c) the AMB-1 strain and (d) the RS-1 strain.

Figure 2

16S rDNA-based phylogenetic relationships of magnetotactic bacteria. Magnetotactic bacteria and pure culture bacterial strains are indicated in bold characters and underlined, respectively.

Figure 3

The two-dimensional electrophoresis proteomic analysis of the BacMP membrane in the following ranges of pIs: (a) 3–10, (b) 4–7 and (c) 6–11.

Figure 4

Scheme of the hypothesized mechanism of BacMP biomineralization.

Figure 5

Schematic for the preparation of functional BacMPs for protein display. The figure is modified from Matsunaga et al. (2007a–c).

Figure 6

Magnetic particles synthesized by partial oxidation in (a–c) the presence and (d–f) absence of Mms6. (g–i) Extracted magnetite from M. magneticum AMB-1. (a,d,g) Low-magnification TEM images, (b,e,h) HRTEM images observed in the [110] zone axis and (c,f,i) ideal morphology of magnetic particles. Pictures are redrawn/modified from Amemiya et al. (2007).

Figure 7

Synthesis of polyamidoamine dendrimers on BacMPs used for DNA extraction. The dendrimers were generated with amine groups derived from AEEA-modified BacMPs. Stepwise growth was repeated until the desired number of generations was obtained.

Figure 8

Construction of antibody-binding ‘Beads on Beads’. (a) The assembly of antibody-binding BacMPs onto streptavidin-coated polystyrene microbeads was established through biotin–streptavidin interaction. (b) Fluorescence microscopy images and (c) fluorescence intensity histograms of Beads on Beads during each conjugation step. Fluorescence intensity histograms were obtained by flow cytometric analysis of more than 10⁴ Beads on Beads particles.

Figure 9

Schematic of the SNP detection procedure. Amplified PCR products were targeted for SNP detection. SNP was determined by measuring the fluorescent intensity of the probes liberated from BacMP complexes by heating.

Figure 10

Overview of an automated plant DNA extraction system (PNE-1080). (a) Automated DNA extraction system, (b) reaction well and (c) schematic of the DNA extraction procedure.

Figure 11

Magnetic detection of streptavidin using biotin–BacMPs. (a) Schematic of the reaction of biotin on the substrate and streptavidin on BacMP. (b) AFM and (c) MFM images of BacMPs on the substrate.

Figure 12

Separation of CD14⁺ cells from PBMCs using protein A–BacMPs bound with antibodies. (a) Fluorescence histograms of the cells separated by flow cytometry from PBMCs (i) before and (ii) after magnetic separation. Upon magnetic separation, the unstained (negative fraction) and stained (positive fraction) fractions were analysed. (b) Microscopic photographs of the (i) separated CD14⁺ cells (ii) before (immature DC) and (iii) after (mature DC) differentiation.