| Microbal repairing to heavy metal pollution with virtue of cheapness, high-efficience and friendly environment, has become a focus study in recent years. In order to investigate the efficiency and mechanism of the removal of Co(Ⅱ) and the oxidation of metallic Co with microorganism, a spetrophotometric method for the determination of Co(Ⅱ) in the laboratory had been established first. Next, microorganism with a strong tolerance to Co(Ⅱ) were screened through plate-screening and shaking-screening methods.. Then the ability of microbial removal of Co(Ⅱ), microbial oxidation of metallic Co, and microbial tolerance to Co radiation were discussed. Finally, the study explored the major chemical groups of the cell involved in the adsorption of Co(Ⅱ) with Fourier transform infrared spectrum and the interaction between microbial cells and Co(Ⅱ) by scanning electron microscopy. The main results were as follows.(1) Method establishment for Co and Co(Ⅱ) determination in microbe medium. The different pH and culture medium affected the determination of Co(Ⅱ), so the releated reasearch was further investmented. a) Method establishment for Co(Ⅱ) determination. The influence rate up to50%at pH7.0in LB, NA and TGY medium.While the pH of medium was set to5.0-6.0, the influence rates were all controled within5%. b) Method establishment Co determination. This research studied the oxidation rate of compositions of fungi medium on metallic Co, such as NH4NO3, NaNO3, MgSO4, sucrose and glucose. Oxidation rate of NH4NO3on the metallic Co was strong and reached to64.32%at72h. While the oxidation rate of NaNO3was only9.66%. So the interaction between Co(Ⅱ) and microbe were discovered in the media with pH5.0-6.0and the modified media were selected as fungal oxidation system.(2) Microbe screening for Co(Ⅱ) removal. Microorganism with a strong tolerance to Co(Ⅱ) were screened through plate-screening and shaking-screening methods. They were Bacillus cereus1, Bacillus cereus2, Bacillus subtilis, Bacillus thuringiensis, Bacillus pseudomycoid.es, Frenny Corynebacterium, Staphylococcus warneri, Deinococcus radiodurans. The Co(Ⅱ) tolerance concentration of these strains were150mg/L,50mg/L,30mg/L,20mg/L,20mg/L,10mg/L,10mg/L and10mg/L respectively. Two methods were used to discuss the bacterial removal rate. One is the method of dead microbial.The microbe concentration, adsorbent concentration, the adsorbent time were controlled and the adsorption rate of Staphylococcus warneri, Bacillus subtilis and Frenny Corynebacterium were relatively high, respectively94.08%,82.86%and63.43%. The other is method of living microbial. The Co(Ⅱ) was removed under shaking culture condition with Bacillus cereus2and Staphylococcus warneri. The removal rate increased gradually with the increase of pH and reached the maximum at72h, were77.10%and98.26%, respectively.(3) Microbial screening of metallic Co oxidation. In this study, through the transparent circle screening and shaking sieving, Penicillium and Aspergillus niger with relatively high ability to produce acid were obtained. In order to control the inoculation concentration, the spore amount-absorbance curve was established. These2strains of fungi were applied to oxidize100mg/L metallic Co, found the concentration of Co(Ⅱ) rised gradually in the medium mixed with Aspergillus niger/Penicillium and the oxidation rate reached the maximum at60h and72h, respectively98.01%and93.96%.(4) Radiation tolerance of microorganisms. The radiation dose of200Gy,500Gy and1000Gy were elected for the irradiation of8strains of bacteria and2strains of fungi. The results showed that the radiation resistant properties of Staphylococcus warneri was the strongest, the radiation dose of1000Gy didn’t affect the growth of Staphylococcus warneri.While fungi were the most sensitive,200Gy had the lethal rate of more than90%on the fungi.(5) A investment on the mechanism of microbial removal for Co(Ⅱ). With the Fourier transform infrared spectrum, the change of Infra-red absorption after the bacteria exposure to Co(II) explained the chemical groups involved in fixing Co(Ⅱ). On the other hand, scanning electron microscope was choosed to explore the bacterial response to Co(Ⅱ) stress at the cellular level. The results showed that the amide and amino mainly adsorbed Co(Ⅱ) in the cell wall. Facing the stress of Co(Ⅱ), bacteria reduced the contact area with Co(Ⅱ) by shrinking, bending or shortening, thereby reducing the harm of Co(Ⅱ)to the cell.In summary, under pH5.0～6.0, Staphylococcus warneri show low tolerance on Co (Ⅱ), while high removal rate and radiation tolerance. On the contrary, Bacillus cereus1own high tolerance on Co (Ⅱ) but low removal rate; the amide and amino of the bacterial cell mainly adsorbed Co(Ⅱ); bacteria reduced the contact area by shrinking, bending or shortening, thereby reducing the harm of Co(Ⅱ) to the cell. In the modified media, Aspergillus and Penicillium showed a high oxidation ability to metallic Co and were sensitive to radiation. Mechanisms for the interaction between cobalt and microbes should be further studied. |
PDF Full Text Request