Biological synthesis of gold nanoparticles by Thermus scotoductus SA-01

[摘要] English: The usual strategy to prepare gold nanoparticles involves the reduction of a gold salt in solution by various reducing agents in the presence of a stabilizer. These particles are mostly spherical with poor monodispersity. An alternative means is to use biological material to mediate particle synthesis. Microorganisms such as fungi have demonstrated the ability to produce nanoparticles of different shapes and sizes extending beyond the scope of chemical means, and the microbial interaction with metals also supply eco-friendly methods for nanoparticle production. It has been hypothesized that the proteins involved in nanoparticle synthesis require a co-factor such as NADH / NADPH, as previous studies have indicated that NADH- and NADPH-dependent enzymes are important factors in the biosynthesis of metal nanoparticles. Thermus scotoductus SA-01, a thermophilic bacterium, isolated from an AngloGold Ashanti mine near Carletonville, Republic of South Africa, was used for purification of a gold(III) reducing and nanoparticle synthesizing protein. This bacterium has the ability to produce gold nanoparticles, and more than one pathway can be followed to produce these particles. A protein was purified to homogeneity by using a combination of several liquid chromatography resins. The N-terminal sequence was obtained by using automated Edman degradation. The protein purified is not a classical oxido-reductase and was identified as an ABC transporter peptide-binding protein (~70kDa). This discovery shows that gold nanoparticles can be produced by proteins other than oxidoreductases. The interaction of the protein extracted and purified from Thermus scotoductus SA-01, as well as the recombinant proteins, with liquid gold under varying physico-chemical conditions have been studied using TEM, EDS, and by measuring the plasmon resonance band, to illustrate the effect on particle morphology and to elucidate the protein mechanism. The size and the shape of particles could, to an extent, be manipulated by controlling the environmental parameters. The purified protein as well as the recombinant proteins was only able to produce nanoparticles in the presence of sodium dithionite and it is thus hypothesized that the donation of electrons via the disulphide bridge in the protein is involved in the reduction of the gold ions. Even though the recombinant proteins had the ability toproduce nanoparticles they were not as efficient as the native protein, but when the optimum parameters for the recombinant proteins are established they could be used in the upscale production of gold nanoparticles or gold nanosheets.

[发布机构] University of the Free State