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Study on Biosynthesis of Silver Nanoparticles Using the Phototrophic Bacteria Rhodopseudomonas Palustris

Author: ChaiChunJing
Tutor: BaiHongJuan
School: University of North
Course: Environmental Engineering
Keywords: Phototrophic Bacteria Silver Nanoparticle Biosynthesis Nitrate Reductase Activity
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 50
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Abstract


Nanostructured materials have bright prospective as a result of their unique physical and chemical properties and their important application in optics, electronics, biomedicine, magnetics, mechanics, catalysis, energy science, and so on. Though there are several approaches to synthesis of silver nanoparticles （AgNPs） in recent years, to achieve the objective of developing low cost, simple and eco-friendly technology, researchers in this field have turned to biological systems. Biosynthesis of silver nanoparticles using bacteria and fungi has attracted considerable attention in this field.The experiment focuses on extracellular biosynthesis of AgNPs using cell filtrate of Rhodopseudomonas palustris. The optimum condition, anti-bacterial property and mechanism were investigated. The study provided experimental base for biosynthesis of silver nanoparticles and lay a foundation for further extension and production. The main contents are as follows:（1） Research on synthesis of silver nanoparticlesSilver nanoparticles were synthesized by adding AgNO3 solution to cell filtrate of Rhodopseudomonas palustris. These nanoparticles were characterized by UV-vis spectrum, X-ray diffraction spectrum （XRD） Transmission electron microscopy （TEM） and high-resolution transmission electron microscope （HRTEM）,etc. UV-vis spectrum of the aqueous medium containing silver ion showed a peak between 420-460nm corresponding to the plasmon absorbance of AgNPs. A comparison of our XRD spectrum with the standard confirmed that the silver particles formed in our experiments were in the form of nanocrystals, as evidenced by the peaks at 2θvalues of 38.45°, 44.48°, 64.69°and 77.62°. TEM and HRTEM micrograph showed the AgNPs were spherical or nearly spherical particles, in the range of 5-20nm. Through the orthogonality experiment, the optimum condition has been obtained: pH 7, temperature 25℃, and concentration of Ag+ solutions 2mM. pH played a major role in size control of the particles.（2） Research on anti-bacterial property of silver nanoparticlesThe antimicrobial activity of AgNPs was tested against Staphylococcus aureus as the model gram- positive bacterial and Escherichia coli as the model gram-negative bacterial. The minimum inhibitory concentration （MIC） and the minimum bactericidal concentration （MBC） were read through the experiment. The results shows that AgNPs exhibits obvious antimicrobial effect, the MIC is 20mg/L and the MBC is 100mg/L. It provided the basic data for the utilization of silver nanoparticles.（3） Research on mechanism for the biosynthesis of silver nanoparticlesThe result shows that challenging the bacteria with silver ions resulted in induction of a new protein with molecular weight c.a. 21.2KD. Increase in the concentration of silver nitrate solution led to increase in nitrate reductase （NR） activity when the concentration was within certain region. The NR activity may be inhibited when the silver ions concentration exceeded a certain limit.

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