Microregulation Of Urease-producing Microorganisms On Heavy Metal Mineralization

Urease-producing microorganisms play an important role in the biomineralization and fixation of heavy metals.In order to explore the micro-regulation mechanism of urease-producing bacteria on the biomineralization process of heavy metals and realize the effective fixation of heavy metals,this thesis focuses on the regulation of nucleation sites of heavy metal mineralization and the regulation of mineralized products.The high polymer polyacrylic acid(PAA)was used to simulate the extracellular polymer of bacterial strains to increase the nucleation sites of minerals,and avoid direct contact between bacteria and heavy metals,reduce the toxicity of heavy metals to cells,and promote the occurrence of biological mineralization process,and the mineralized products have a certain low temperature stability.The effect of polymer on metabolism was further analyzed by metabonomics.In order to achieve effective fixation of heavy metals,based on the principle of co-crystallization,the morphology of biological mineralized products is regulated,and the obtained co-crystallization products of heavy metals can still maintain high stability in a low p H environment,providing important theoretical basis for the subsequent remediation of heavy metals in contaminated sites.The main research contents include the following parts:(1)The urease producing bacteria were identified by molecular biology.The results showed that the strain had high homology with Staphylococcus succinis and was named J3.(2)To explore the regulation of urease-producing microorganisms on the nucleation sites of heavy metal biomineralization.After coating J3 with different concentrations of PAA,the medium without PAA was used as the control group to explore its biomineralization effects on Cu,Ni,Mn and Zn.Measurement in the process of cultivating the OD600,p H and urease activity to observe the growth of the J3 condition,in the case of PAA coated growth is restrained small,determined by MTT colorimetric method showed that cell activity is higher,the ICP determination of heavy metal concentration in the supernatant,heavy metal fixed rate over 90%,FT-IR results show that heavy metals are generated carbonate minerals,Among them,0.5%PAA had the best effect.In addition,the number of viable cells of J3 remained at a high level at 4℃ after PAA coating,and it still had a certain urease activity,indicating that the low temperature resistance of J3 was improved after PAA coating.The results showed that the addition of PAA could increase the nucleation sites of minerals,avoid direct contact,reduce the toxicity of heavy metals to bacteria,and realize the micro regulation of nucleation sites(3)In order to further explore the regulation mechanism of urease-producing microorganisms on nucleation sites,the effect of high molecular weight polymer polyacrylic acid(PAA)on J3 metabolites was investigated by metabonomics.According to the above research results,the concentration of 0.5%PAA was selected,and Cu and Mn were selected as two representative heavy metals.The unsupervised and supervised discriminant methods of PCA,PLS-DA and OPLS-DA were used to determine the metabolic differences of the strains before and after PAA addition,and then analyze their differential metabolites and metabolic pathways.The differential metabolites under Cu stress were mainly amino acids,and the main differential metabolic pathway was glutathione metabolism,which generated glutathione scavenging free radicals to resist Cu stress.Under Mn stress,the differential metabolites are mainly organic acids and nucleotide substances,and the main differential metabolic pathway is pyruvate metabolism,which provides energy to complete the oxidation energy supply process and provide energy to resist the stress of heavy metals.(4)In order to further explore the micro-regulation mechanism of the ureaseproducing bacteria on the biomineralization of heavy metals,higher fixation efficiency of heavy metals can be obtained from regulating the micro-morphology of the mineralized products.Taking lead as an example,calcium carbonate crystals are prepared by biological mineralization,and replacement adsorption reaction is carried out on lead.SEM and TEM show that two kinds of method,got the ball aragonite and calcite calcium carbonate,after the adsorption of lead,ICP results show that the concentration of calcium increased with the concentration of lead,this suggests that lead to replace the calcium in calcium carbonate crystal lattice,formed calcium lead cocrystallization,The morphology of the crystals is obviously different before and after replacement.XRD results further indicate that the mineral is cocrystallization of Ca-Pb.Compared with the eutectic crystals and pure lead carbonate obtained by chemical method,the eutectic crystals of calcium and lead carbonate obtained by biological mineralization method have better stability and lower dissolution rate of heavy metals under acidic conditions.Higher fixation efficiency of heavy metals can be achieved by regulating the micromorphology of mineralized products.In this thesis,by using polyacrylic acid,a plant to produce urease bacteria of nucleation sites,promoted the biomineralization process,metabonomics technology further clarify treatment effect,and use the method of biological mineralization were to micromanage the mineralized product,realize effective fixed of heavy metal,heavy metal repair for subsequent contaminated sites provide a theoretical basis.