Study On Synthesis Of Silver Nanoparticles Mediated By Bacteria

This study selected soil samples, which derived from Maoer Mountain forest farm of Northeast Forestry University, as experimental material to isolate bacterial strain zxw01 using the method of silver nitrate concentration gradient. Morphological characteristics, physiological and biochemical characteristics and 16 SrDNA sequences analysis were employed to identify the bacteria. Results showed that the bacteria was gram-positive with rod-shape, and it cannot use xylose and arabinose. Analysis of 16 SrDNA sequences indicated that the bacteria show 99.8% similarity with Bacillus amyloliquefaciens. Based on the morphological, physiological-biochemical characteristics and the analysis of the 16 SrDNA, the strain was identified as Bacillus amyqueciens eventually. Then biological characteristics of the bacteria were detected. Results suggested that the bacteria can grow in the modified LB medium containing 0.3 mmol/L AgNO3, which indicated the bacteria show certain resistance to silver. The optimum growth temperature of the strain was about 35℃ and the optimum pH was about 7.Silver nanoparticles was biosynthesized using bacteria culture and silver nitrate and UV vis,XRD, TEM, HRTEM,FTIR were used to characterize silver nanoparticles. The results showed that spherical and near spherical nanometer silver particles were synthesized by the combination bacteria culture and silver nitrate. Silver nanoparticles was face-centered cubic structure with monodisperse and good crystalline. The average diameter of nano silver particle was 15 nm. Silver nanoparticles distributed inside and outside cell and the size distributed inside was much smaller, FTIR spectrum reveals that proteins must be present on the surface of silver nanoparticles.Thermogravimetric analysis of nano silver particles indicated that the yield of silver nanoparticles reached 80.6%. From the bacteriostatic experiment, we found that minimal inhibitory concentrations for E. coli of silver nanoparticles was 20 mg/L and the minimum inhabitory concentration was 60 mg/L.The living bacteria count for E.coli in Logarit hmic growth phase decreased rapidly in 30 min when under the culture conditions of silver nanoparticles was 60 g/mL. At 2 h,fatality rate of silver nanoparticles reached to 98% and the E.coli must be basically killed.Catalytic effect to Methyl orange was studied using the silver nanoparticles made by strain zxw01 as a catalyst. Studies showed that silver nanoparticles has obvious promotion effect on the degradation rate of methyl orange under sunlight,the degradation rate was up to 81.5% after 3h.Silver nanoparticles had the activity with catalytic degradation to Methyl orange under the light and the result was the opposite in dark.Finally, SDS-PAGE electrophoresis was employed to study the mechanism of silver nanoparticles. Results showed that the strain produced two new proteins after adding silver nitrate, whose sizes was 60 kDa and 33 kDa respectively. Proteins attached to silver nanoparticles can be separated and the size was about 33 kDa, which indicated that the protein was related to stability of silver nanoparticles and can inhibit the agglomeration of nanoparticles. Another protein was responsible for the reduction of Nano silver. According to the experimental results, we proposed a mechanism of reduction nano silver. At first, silver ion made the combination with receptors on the surface of the bacteria and at the same time, signals were passed the to bacteria and induced special protein coding genes begin to express, and two kinds of new protein were produced (part of proteins was secreted to the outside of the cell), one was responsible for the reduction of silver ion and the other was responsible for the stability of silver nanoparticles. Both within the bacterial cells and outside the cells,the nanosilver were synthesized.