Research On The Preparation Of Nano-selenium And Antioxidant Activity Using Bacillus Licheniformis

Selenium is one of the essential trace elements of organisms.It has various effects on the body such as cell repair,antioxidant,immunity improvement,growth promotion,and cancer prevention.Selenium deficiency in the body can induce various diseases such as organ dysfunction,growth retardation,abnormal thyroid function,Keshan disease,Kashin-Beck Disease,and so on.Selenium exists mainly in the form of inorganic selenium in chemical form,inorganic monomeric selenium,and organic selenium.Since animals cannot synthesize selenium directly,they can only consume selenium from their diet.As the market demand for selenium supplementation increases,it is extremely important to explore a more healthy and scientific way of selenium supplementation.Bacteria,fungi,actinomycetes,and other microorganisms can synthesize selenium nanoparticles.The chemically synthesized monolithic selenium has poor stability,easy to agglomerate,and is easy to turn gray or black when left for a long time.In comparison,biological nano-selenium with protein as the nucleus and red monolithic selenium as the membrane has better stability is easy to be absorbed by the body and has higher safety.Bacillus licheniformis is commonly used in the development of crop disease biologics and feed additives and is a high-safety biocontrol bacterium.In this study,Bacillus licheniformis（Bl-001）was found to be able to grow in a modified LB liquid medium with a sodium selenite concentration of 120μg/m L.After 60 h of incubation in a shaking incubator at 30°C and 150 r/min,the spiked solution was red in color and the conversion rate of sodium selenite reached 39.520%.This is because Bl-001 reduced Se O₃^2-into red monolithic selenium,thus indicating that Bl-001 has a good ability to synthesize red nano selenium in higher sodium selenite concentration solution.In order to improve the conversion rate of Bl-001 to sodium selenite and increase the synthesis capacity of monoselenium,while reducing the adverse environmental impact of residual sodium selenite.Further,the effects of single-factor and multi-factor culture conditions on the ability of Bl-001 to convert sodium selenite were optimized by using Bl-001 as the test strain in order to optimize the conditions for the synthesis of nanoselenium by single-factor and response surface,and the experimental results showed that（1）The optimal conditions for the synthesis of red monolithic nanoselenium by Bl-001 were sodium selenite concentration 88.4μg/m L,inoculum amount 2.1%,incubation time 60.6 h,p H 6.2,and the conversion rate of sodium selenite was up to53.42%.（2）Using this optimized condition to incubate Bl-001,selenium nanoparticles were prepared,which were regular spherical particles with particle sizes in the range of 90-200 nm.The characteristic peak of elemental Se appeared at 1.4 ke V,and the relative content of elemental Se of the particles reached up to 82.07%.（3）The surface structure of Se NPs was analyzed by infrared spectrometer,and it was found that the surface may have bound organic matter such as proteins and polysaccharides.（4）At the same time,the biological activity of the nano-selenium was analyzed,and it was found that the nano-selenium has strong antioxidant activity,and the lower concentration of 0.8 mg/m L nano-selenium solution has high scavenging rate for DPPH（1,1-diphenyl-2-picrylhydrazyl）,ABTS(2,2’-azino-bis（3-ethylbenzothiazoline-6-sulfonic acid）,and O₂^-（superoxide anion）radicals,which indicates that the nano-selenium has good antioxidant biological activity.This research result enriches the pathway of microbial transformation and synthesis of selenium nanoparticles and provides a basis for the biosynthesis of selenium nanoparticles using Bacillus probiotics.