Research On Characterization,antimicrobial Ability,and Toxicity Of Selenium Nanoparticles Biosynthesized By Microbes

In recent years,various microbes have been regarded as potential biocatalysts to reduce selenite to less toxic selenium nanoparticles(SeNPs).In this process,the biotoxicity of selenite can be greatly decreased and the biosynthesized SeNPs can be further used as a high value added catalytic or antimicrobial agents.With extensive use of SeNPs,mass of nanoparticles is bounded to be released into environmental media.However,the toxic mechanism and safety threshold of SeNPs are still not explicit enough.Herein,the biosynthesis ability of SeNPs were firstly compared between bacterium and fungus based on previous studies.Then,the antibacterial properties of as-synthesized SeNPs as well as the toxicity effects of biological and chemical SeNPs were investigated.The main contents are as follows:The abilities of biosynthesizing SeNPs by both Mariannaea sp.HJ and Providencia sp.DCX were compared.It was shown that 73.15%of Se O₃^2-could be reduced in 168 h by fungus HJ.As for bacterium DCX,the reduction rate of Se O₃^2-was 96.14%within 24 h.The active components in extracellular EPS and extracellular extracts of bacterium DCX played a major role in the reduction of Se O₃^2-,while the reduction process of fungus HJ was mainly occurred in intracellular cells.Besides,ETSA content determination and electron transport chain shielding experiments indicated that bacterium DCX obtained electrons through the electron transport chain for the synthesis of SeNPs.And coenzyme Q was the most important electron transport carrier in the reduction process.The SeNPs,synthesized by bacterium DCX,were applied to investigate the antibacterial properties of model bacteria,including Gram-positive(S.aureus,B.cereus and B.subtilis)and Gram-negative bacteria(P.aeruginosa,E.coli and V.parahemolyticus).It was shown that the biosynthesized SeNPs demonstrated strong inhibition activity against the growth of these pathogens(except for B.subtilis).When treated with 500 mg/L SeNPs,most of the tested bacteria were destructed within 12 h.But among them,both the growth inhibition effects and locally destruction activity of bio-SeNPs against Gram-negative bacteria were much better than that of Gram-positive bacteria.SEM images showed that the cell membranes of each strain were damaged to varying degrees after treated with SeNPs,which could further lead to the leakage of proteins and polysaccharides outside cells.Besides,the extracellular ROS intensity were also significantly increased with the treatment of SeNPs,suggesting that oxidative damage may play the significant role in the antibacterial processes.The toxic effects of biological and chemical SeNPs on zebrafish were further investigated.It was found that the LC₅₀ values of chemical and biological SeNPs were separately 0.699 mg/L and 1.668 mg/L,indicating that the chemical SeNPs was more toxic than that of biological ones.The changes of different indexes in zebrafish liver and gills after treated with the biological and chemical SENPs were also measured.It could be seen that the content of GSH,SOD,ROS,etc.were increased and the Ach E enzyme activity was significantly decreased after the addition of these two nanoparticles.Besides,they could also induce the secretion of LDH in the liver and the inhibition of Na⁺K⁺-ATPase activity in the gills.Therefore,SeNPs might lead to certain toxic effects on zebrafish by causing oxidative damages,nerve conduction disorders and osmotic pressure disturbances.However,the toxic effects of biological SeNPs on zebrafish liver and gill were significantly decreased compared with chemical SeNPs.