Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences, 410049, Saratov, Russia,
Microb Ecol. 2014 Jan;67(1):155-60. doi: 10.1007/s00248-013-0329-6. Epub 2013 Nov 26.
For the soil nitrogen-fixing bacterium Azospirillum brasilense, the ability to reduce AuCl4 and to form gold nanoparticles (GNPs) has been demonstrated, with the appearance of a mauve tint of the culture. To validate the shapes and chemical nature of nanoparticles, transmission electron microscopy (TEM) and X-ray fluorescence analysis were used. For the widely studied agriculturally important wild-type strains A. brasilense Sp7 and Sp245, GNPs formed after 10 days of incubation of cell biomass with 0.25 mM AuCl4 were shown (using TEM) to be mainly of spherical form (5 to 20 nm in diameter), with rare occasional triangles. In the course of cultivation with AuCl4, after 5 days, a mauve tint was already visible for cells of strain Sp245.5, after 6 days for Sp245 and after 10 days for Sp7. Thus, for the mutant strain Sp245.5 (which has significant differences in the structure and composition of cell-surface polysaccharides as compared with Sp245), a more rapid formation of GNPs was observed. Moreover, their TEM images (also obtained after 10 days) showed different shapes: nano-sized spheres, triangles, hexagons and rods, as well as larger round-shaped flower-like nanoparticles about 100 nm in size. Since by the time of GNP formation in our experiments the cells were found to be already not viable, this confirms the dominating role of cell surface structure and chemical composition in shaping the GNPs formed in the course of AuCl4 reduction to Au(0). This finding may be useful for understanding the natural biogeochemical mechanisms of gold reduction and formation of GNPs involving microorganisms. The data obtained may also help in developing protocols for environmentally friendly synthesis of nanoparticles and possible use of bacterial cells with modified surface structure and composition for their fabrication.
对于土壤固氮菌 Azospirillum brasilense，已经证明其具有还原AuCl4并形成金纳米颗粒（GNPs）的能力，培养物呈现出淡紫色调。为了验证纳米颗粒的形状和化学性质，使用了透射电子显微镜（TEM）和 X 射线荧光分析。对于广泛研究的农业重要野生型菌株 A. brasilense Sp7 和 Sp245，在用 0.25 mM AuCl4孵育细胞生物质 10 天后形成的 GNPs（使用 TEM）主要呈球形（直径为 5 至 20nm），偶尔有三角形。在 AuCl4培养过程中，Sp245.5 细胞在 5 天后已经呈现淡紫色，Sp245 在 6 天后，Sp7 在 10 天后。因此，与 Sp245 相比，突变株 Sp245.5（其细胞表面多糖的结构和组成有显著差异）观察到更快形成 GNPs。此外，它们的 TEM 图像（也在 10 天后获得）显示出不同的形状：纳米尺寸的球体、三角形、六边形和棒状，以及约 100nm 大小的较大圆形花状纳米颗粒。由于在我们的实验中形成 GNPs 时发现细胞已经不再存活，这证实了细胞表面结构和化学成分在形成AuCl4还原为 Au(0)过程中形成的 GNPs 形状方面起着主导作用。这一发现可能有助于理解涉及微生物的金还原和 GNPs 形成的自然生物地球化学机制。获得的数据还可能有助于开发用于环境友好型纳米颗粒合成的协议，并可能使用具有改性表面结构和组成的细菌细胞来制造它们。
