| Selenium(Se)is an essential trace element for life activities,and plays important roles in maintaining redox balance,regulating the immune system,and protecting DNA and chromosomes from oxidative damage.Selenium mainly exists in the forms of inorganic selenium compounds,organic selenium compounds and elemental selenium.Among the different forms of selenium,the toxicity of inorganic selenium compounds is the highest,followed by the organic,and the elemental is the weakest.Lactic acid bacteria,as the most widely used strain in the field of food fermentation,many strains have been reported to have the function of biosynthesis of selenium nanoparticles(Se NPs).When eating selenium-enriched foods or health foods fermented by lactic acid bacteria,people can not only supplement trace elements,but also obtain the probiotic effects brought by the strains.Therefore,lactic acid bacteria can be used as good carrieries and transformants for the synthesis of Se NPs.And using selenium-rich lactic acid bacteria to make new selenium supplement products has bright prospects.In this study,we first screened a test strain capable of reducing sodium selenite to produce Se NPs-Lactobacillus plantarum WZ8.Secondly,Se NPs with different sizes were obtained by changing the culture conditions,and the correlation between the size and the biological activity was explored in vitro.Based on the results of the single-factor test and the Plackett-Burman(PB)screening test,the RSM was used to optimize the culture conditions.In addition,the mechanism of Se NPs synthesis by strain WZ8 was also preliminary explored.The following results were obtained through the above tests:(1)L.plantarum WZ8 was selected as a carrier to reduce sodium selenite.After 7 hours,sodium selenite was added to 80 ?g/m L and the centrifuge was collected after 36 hours of incubation.The results revealed that the spherical particles were Se NPs,which were came from scanning electron microscope,energy spectrum analysis and nano laser particle size analyzer.(2)The antibacterial test results showed that the Se NPs with different sizes had different inhibitory effects on the four food-borne pathogens.For the same pathogenic bacteria,Se NPs with smaller size had stronger inhibitory effects than larger-sized.Antioxidant activity tests found that different sizes lead to differences in total reducing power and free radical scavenging power of Se NPs.Compared with the larger-sized,the smaller-sized Se NPs have stronger free radical scavenging and reducing power.(3)The range of values of initial p H,culture temperature,inoculation amount,sodium selenite concentration,and stress time were determined by single factor experiments.On this basis,the PB test results found that the initial p H and sodium selenite concentration had significant effects on the size and recovery of the Se NPs,while the stress time only had a significant effect on the size.Finally,the optimal culture conditions for the preparation of Se NPs by L.plantarum WZ8 were determined by RSM.The initial p H was 7.88,the concentration of sodium selenite was 74.04 ?g/m L,and the incubation time was 19 h as the required conditions.(4)Transcriptomics analysis of L.plantarum WZ8 treated with sodium selenite(80 ?g/m L)based on RNA-seq sequencing,1760 DEGs was found,of which 884 genes were up-regulated and 876 genes were down-regulated.The GO analysis results showed that DEGs were mainly distributed in gene expression,organonitrogen compound biosynthetic process,organonitrogen compound metabolic process,cells,cell part,catalytic activity,and RNA binding.Analysis of the KEGG revealed that DEGs were mainly involved in metabolic pathways such as oxidative phosphorylation,selenium compound metabolism,carbon metabolism,pyruvate metabolism,cysteine and methionine metabolism.Transcriptome results showed that genes related to Trx R and cysteine synthase were up-regulated,which showed that L.plantarum WZ8 may reduce sodium selenite to elemental selenium through the Trx R system. |
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