Influencing Factors And Mechanism Of Uranium (U(Ⅵ)) Mineralization By Magnetotactic Bacteria In Iron-Containing Environments

Radionuclide uranium(²³⁵U)is the main fuel for nuclear power operations in the world.However,a large amount of uranium containing tailings and tailings water are generated during uranium mining and smelting,leading to varying degrees of pollution of surrounding groundwater.The remediation of uranium contaminated groundwater is an urgent environmental issue to be addressed.In polluted groundwater,uranium mainly exists in the form of dissolved hexavalent uranium（U（Ⅵ））.The use of microbial reduction method to reduce easily soluble and migratory U（Ⅵ）to insoluble U（Ⅳ）is currently an important technology widely used in uranium pollution control.As the main species in sediments,U（Ⅳ）is still easily oxidized and reactivated by strong oxidants such as Fe（Ⅲ）,NO₃^-,and O₂ in the aqueous phase,indicating that the reduction mineralization of uranium is easily influenced by Fe（Ⅱ）and Fe（Ⅲ）in groundwater,while Fe（Ⅱ）/Fe（Ⅲ）often accompanies uranium in groundwater.Therefore,solving the bottleneck problem of the re-release of U（Ⅳ）generated in microbial reduction methods has become very important.In the preliminary research,it has been found that magnetotactic bacteria can mineralize and fix U（Ⅵ）in Fe-containing systems,generating stable uraninite.However,the external environment has a significant impact on the mineralization process of magnetotactic bacteria.Therefore,this article focuses on studying the effects of the valence state of iron ions and the concentrations of iron,uranium ions,HCO₃^-,and chelating agents on the synthesis of uraninite.By measuring the growth curves of MSR-1 in different systems,using the transmission electron microscope to track and observe the changes in the form and composition of uraninite in magnetotactic bacteria MSR-1,using the microbalance to determine the yield of uraninite,and using inductively coupled plasma mass spectrometry to analyze the uranium content in uraninite,preliminarily analyzing the influence of the valence of iron ion and the concentration of iron,uranium ion,HCO₃^-and chelating agent on the synthesis of uraninite.Meanwhile,four MSR-1 growth systems without synthesis of uraninite（A1）,synthesis of a small amount of uraninite（A2）,synthesis of a large amount of uraninite（A3）,and inhibition of uraninite synthesis（A4）were constructed,and the transcriptomic gene libraries of MSR-1 in the four differential systems were constructed by extracting total RNA from the four differential systems,and the differential expression levels of MSR-1 genes in the different systems were analyzed to obtain differentially expressed genes using the reference genome of magnetotactic bacteria in NCBI as a benchmark.This study provides a new approach for treating U（Ⅵ）pollution in iron-containing systems.The main conclusions and results are as follows:1.Changing the valence state of iron ions and the concentration of iron and uranium in the culture medium had no significant impact on the growth curve of magnetotactic bacteria,but the arrangement of magnetosomes is affected by the concentration of U（Ⅵ）.The higher the concentration of uranium,the more disordered and dispersed the arrangement of magnetosomes.The concentration and proportion of iron and uranium ions had an impact on the synthesis of uraninite.After analyzing different concentration gradients of 0-80μM U（Ⅵ）,founding that the uranium content is highest at the concentration of 40μM U（Ⅵ）,and the uranium content produced under Fe（Ⅲ）conditions is higher than that under Fe（Ⅱ）conditions.2.After adding Na HCO₃ to the culture medium,the erosion of UO₂²⁺on the bacterial body and destruction of the cell membrane decreased,indicating that the solubility of UO₂²⁺in the culture medium after adding Na HCO₃ increased.Changing the concentration of Na HCO₃ in the culture medium has an impact on the synthesis of uraninite.Under the Na HCO₃ containing mineralization system,the uranium content in the magnetite increases with the increase of Na HCO₃ concentration.3.After adding various chelating agents to the culture medium,the erosion of UO₂²⁺on the bacterial body and destruction of the cell membrane decreased,indicating that the chelating agent in the culture medium coated uranium ions,increasing the solubility of uranium ions.In the three types of chelating agent mineralization systems,the uranium content in magnetosomes increases with the increase of chelating agent concentration.4.RNA extraction and transcriptome analysis.Transcriptome analysis of four differential systems showed that there were 195 differentially expressed genes associated with the synthesis of small amounts of uraninite,124 differentially expressed genes associated with the synthesis of large amounts of uraninite,and 582 differentially expressed genes associated with the inhibition of uraninite synthesis.Differentially expressed genes mainly enrich molecular functions related to catalytic and binding activities,and also participate in biological processes such as metabolic and cellular processes.In addition,some genes are also involved in the redox control of uranite synthesis.The differentially expressed genes are significantly enriched in pathways related to multiple biological processes,mobility,oxidoreductase activity,and redox processes.