Study On Intracellular Response Mechanism Of Uranium Adsorption And Enrichment By Hydrodictyon Reticulatum

With the increasing demand for uranium(U)resources in national defense,military industry and nuclear power industry,it is inevitable to produce a large amount of U containing low-level radioactive wastewater in the process of mining and utilizing U resources.How to effectively treat these large amounts of low-level wastewater is directly related to the sustainable development of the nuclear industry,which is an urgent major problem to be solved.There are thousands of Hydrodictyon reticulatum bodies in the cells.H.reticulatum are natural cell embedded bodies with strong reproductive ability and wide adaptability.They have great application potential for the adsorption and enrichment of radionuclides and heavy metals in polluted water.However,the mechanism of U absorption,transport,micro distribution and stress physiological response of H.reticulatum is not clear.In this study,wild-type H.reticulatum were used as materials,different U treatments were set,and the following key scientific problems proposed and to be solved in this reseach were explained from the aspects of transcriptome,metabolome and growth and development response by using stress physiology,biochemistry and multiomics technology:the absorption and transport of U by wild-type H.reticulatum population cell embedding body under U stress microdomain distribution,physiological response to stress and detoxification mechanism,and molecular response mechanism of transcriptomics and metabolomics.The main results are as follows:(1)The p H adaptation range of wild-type H.reticulatum was 6?10,and the optimum value was 9;The temperature range was 2.6?38?,and the optimum temperature was 25?;There was no significant difference in growth at light intensity of 3000 Lx?5000 Lx;Phosphate(<0.07011 m M)and NO₃-N promoted its growth.As a stereotyped population,H.reticulatum propagate asexually from zoospores,and its growth characteristics are basically similar to the growth trend of single-cell and large algae.However,the growth and zoospore formation of H.reticulatum are related not only to environmental nutrition,but also to the rate at which H.reticulatum consume intracellular stored nutrients,and the formation of zoospores is related to growth stress.There are tens of thousands of H.reticulatum in the cells.As a natural cell embedded body,it has strong reproductive ability,high U enrichment and wide adaptability.It has the potential to screen as a new germplasm for biological purification of low-level radioactive wastewater containing U.(2)Uranium in the enrichment system was mainly enriched by H.reticulatum in the form of UO₂(OH)₃^-and Ca UO₂(CO₃)₃^-2;The enrichment methods of U by H.reticulatum include chemical and physical adsorption,in which chemical adsorption was more than physical adsorption;The enriched U was mainly compartmentalized in vacuoles and pyrenoid;The enrichment model of U by H.reticulatum met the Langmuir adsorption isotherm equation and Freundlich adsorption isotherm equation.H.reticulatum had high affinity for U and was an active enrichment process.H.reticulatum could reduce U from0.104 mg/L to 0.034 mg/L in water(lower than 0.05 mg/L required by the state for the discharge of U containing wastewater).The maximum enrichment amount q_m could reach13.532 mg/g when the content of U in water was less than 1.1 mg/L,indicating that the algae has the ability of super enrichment in the purification of low-level radioactive wastewater containing U.(3)Under U stress,H.reticulatum responds to U stress by regulating the content of malonic dialdehyde(MDA)and H₂O₂ in cells,the release rate of O.₂^-and the activities of superoxide dismutase(SOD),catalase(CAT),peroxidase(POD)and other enzymes in cells.When U stress is more than 10 mg/L,the production of superoxide anion leads to the delay of cell self-regulation and irreversible damage of cell membrane.Glutathione(GSH)plays an important and active role in scavenging intracellular reactive oxygen species of H.reticulatum under U stress,which is related to glutathione reductase(GR)accelerating the conversion of GSH and glutathione oxydized(GSSH).(4)Transcriptome sequencing analysis showed that 5959 differentially expressed genes(DEGs)were obtained after 30 mg/L U stress for 72 h.Among them,2534 DEGs were up-regulated and 3425 DEGs were down regulated.Go enrichment analysis showed that it was mainly related to molecular functions such as dehydrofolate reductase activity,ribosomal structure and biological process of translation.Keeg analysis showed that DEGs were mainly enriched in cell process(DEGs,n=126),environmental information processing(DEGs,n=112),genetic information processing(DEGs,n=411)and metabolism(DEG,n=583),indicating that U had the most significant stress effect on the metabolism of reticulum;DEGs were significantly mapped to 179 KEGG metabolic pathway,among which ribosome metabolic pathway(ko03010)was most significantly affected,and DEGs mapped in cysteine and methionine metabolism(ko0070)were significantly up-regulated,Thirdly,the number of DEGs mapped to starch and sucrose metabolism(ko00500)related to energy regulation.(5)Based on the combined analysis of transcriptome data and metabolome data,425differential metabolites were detected and 62 metabolic pathways were mapped in KEGG database.The synthesis of GSH under U stress was closely related to the metabolism of cystine and methionine,as well as the differential expression of key genes such as cys E cys K and gsh A under U stress,which explains the resistance response mechanism of H.reticulatum to U stress at the molecular level.This study will pave the way to enhance the U enrichment and resistance mechanism of H.reticulatum,and provides materials for its application research in U remediation.