Rhizosphere Microbial Diversity Of Selenium-enriched Plants And Isolation And Functional Identification Of Selenium Reducing Bacteria

Selenium is a trace element necessary for both humans and animals.It plays an important biological function in the body,the most important of which is the antioxidant function.Human body cannot synthesize selenium directly,and can only obtain selenium by eating or drinking.Lack of selenium will cause various diseases.Although the daily selenium intake required by the human body is very low,it is difficult for many people in selenium-deficient areas to supplement selenium from daily food and drinking water due to the uneven geographical distribution of selenium.It is an effective way to supplement selenium by taking selenium supplements.Inorganic selenium can easily cause toxic reactions in animals for its narrow safety range.Although organic selenium has greatly improved compared to inorganic selenium,there are still many problems.In recent years,studies have shown that elemental nano-selenium is a form of selenium with high antioxidant activity,immune regulation activity and safety.The existing elemental nano-selenium prepared by chemical methods has poor stability,and have to add dispersants and protective agents,resulting in complicated procedures and high costs.The purpose of this article is to produce elemental nano-selenium by microbial biotransformation and explore new possibilities for industrial production of nano-selenium.In this paper,16 S rDNA sequencing and metagenomic sequencing technology were used to study the microbial diversity of selenium-enriched soil in Enshi,Hubei.First,16 S rDNA sequencing technology was used to study the soil microbial diversity along the environmental gradients in selenium-rich areas.Four groups of soil samples were studied: selenium-rich soil samples without plants(B1),Soil samples around selenium-rich plants(B2),rhizosphere soil sample of selenium-enriched plant(R1),and root surface soil sample of selenium-enriched plant(I1).The results showed that B2 and R1 had the highest microbial diversity,and I1 had the lowest microbial diversity.In terms of community composition,each sample also shows a large difference.The two samples of B2 and R1 are the closest.The Proteobacteria phylum is the phylum with the largest proportion in these two samples,accounting for about 35%.The Euryarchaeota phylum is the most abundant phylum in the B1 sample,accounting for more than 60% of the entire sample community composition.The I1 sample is relatively simple.Cyanobacteria phylum occupies an absolute advantage in the I1 sample with an abundance of about 93%.Secondly,16 S rDNA sequencing technology was used to study the diversity of microbial communities in the rhizosphere soil of plants in selenium-rich areas.Using soil sample B1 as a comparison,three seleniumrich plants rhizosphere soil samples R1,R2 and R3 were collected.Rhizosphere soil samples are very close in microbial community composition and diversity index,and the data results also agree with the previous analysis results.Finally,the microbial community diversity in the rhizosphere soil of plants was analyzed by metagenomic sequencing technology,and it was found that the gene abundance of the B1 sample was much higher than that of the other three groups.A strain was subsequently selected from the selenium-enriched soil and identified as Pseudomonas sp by 16 s rDNA sequencing analysis.After SEM-EDX analysis and XPS analysis,it was found that this strain of Pseudomonas can reduce sodium selenite to elemental nano-selenium particles.Observation under TEM showed that the elemental nano-selenium particles produced by the bacteria existed inside and outside the cell,and the biological elemental nano-selenium reduced by Pseudomonas can be obtained by sucrose density gradient centrifugation.Through the research in this paper,we have a further understanding of the diversity of plant rhizosphere microorganisms in selenium-rich areas,which has a certain reference role for further research on selenium-rich microorganisms in the future.Secondly,the isolation of sodium selenite-reducing strains provides the possibility for the industrial production of biological nano-selenium in the future,which has a certain guiding effect on the production of nano-selenium by microorganisms.