Anaerobic Reduction Of U(Ⅵ) By Bacillus Sp.X02 And Its Electron Transfer Mechanism

In order to investigate the electron transfer mechanism of microbial direct reduction of U(Ⅵ)in water under anaerobic conditions,this research screened a facultative anaerobic bacteria Bacillus sp.X02 from a uranium-contaminated underground sediment in a decommissioning uranium tailings pond in southern China.Microbial reduction of U(Ⅵ)were performed in an anaerobic micro-model envronment constructed in laboratory,and Bacillus sp.X02 was used to reduce U(Ⅵ)in water under different culture conditions.SEM-EDS,XPS,FTIR and XRD were used to characterize the reduction products of U(Ⅵ)in solution.The redox status of cytochrome c of Bacillus sp.X02 during U(Ⅵ)reduction was detected by Raman spectroscopy.The process of microbial reduction of U(Ⅵ)was investigated using electrochemical techniques.A Bacillus sp.X02-U(Ⅵ)dual-compartment research system was constructed to characterize the electron transfer process of microbial reduction of U(Ⅵ).The experimental results showed that the U(Ⅵ)removal rate in the solution reached 93.32%and the reduction rate was 62.43%when the inoculation size of Bacillus sp.X02 was 4%(OD600=2.0),glucose was used as the electron donor,the U(Ⅵ)concentration was 100 mg/L.However,when the electron transfer inhibitor N3Na was added,the reduction rate of U(Ⅳ)was reduced by 25.37%,indicating that U(Ⅵ)reduction is related to the electron transfer of microorganism.Raman spectroscopy results show that cytochrome c as an electron mediator mediates the electron transfer process of reduction U(Ⅵ)by X02.The X02 reduction of U(Ⅵ)produced a precipitate containing both U(Ⅵ)and U(Ⅳ),which may be insoluble Lanthinite((U2(UO2)4O6(OH)4(H2O)4)(H2O)5)and Calcium Uranyl Oxide Hydroxide Hydrate(Ca1.5(OH)[(UO2)6O4(OH)6]·7H2O)minerals.The dual-chamber research system characterized the reduction process of U(Ⅵ).The increase of the external circuit indicated that U(Ⅵ)in the cathode chamber solution can be reduced directly by receiving electrons transferred from the microorganisms in the anode chamber.The reduction is carried out in the process of U(Ⅵ)→U(Ⅴ)→U(Ⅳ)when the electrolyte pH is 4.0.The iTRAQ proteome sequencing technology showed that the total number of differentially expressed proteins of microorganisms in the reduction process is 229,of which the number of significantly up-regulated and down-regulated proteins is 90 and 139,respectively.In GO functional classification,these differential proteins are mainly enriched in the cellular components,regulation and metabolism in biological processes electron carrier,enzyme regulation,and transfer activity in processes and molecular functions.The analysis results of KEGG Pathway showed that electrons were mainly transferred through oxidative phosphorylation signaling pathwa in X02.And the analysis of differential expression protein showed that the expression of 9 proteins in the oxidative phosphorylation signaling pathway of X02 was inhibited,and the activities of cytochrome c and ATP synthase were decreasedIn general,a facultative anaerobic bacterium Bacillus sp.X02 with U(VI)reducing ability was screened,which can use glucose as electron donor under anaerobic conditions.Electrons can be produced during the oxidation of NADH(or FAD)by the complex Ⅰ(or complex Ⅱ)through glycolysis(or the tricarboxylic acid cycle),and the electrons can be transferred to complex Ⅲ via the ubiquinone(coenzyme Q).Then the electrons were transferred to complex Ⅳ mediated by cytochrome c.Finally,the electrons were transfered to U(Ⅵ)in solution and generate the undissolved lanthinite and calcium uranyl oxide hydroxide hydrate.Uranium stress also inhibited the reduction of U(Ⅵ)by Bacillus sp.x02.