Characteristics Of Selenium Accumulation And Transformation By Lactobacillus Sp. JZ07

Selenium?Se?,an essential micronutrient with antioxidant properties.Se deficiency can cause a variety of endemic diseases.Selenium is found in nature mainly in the form of highly toxic selenite(SeO₃^2-).Compared with inorganic selenium,organic selenium and nano-Se have an advantage of higher security.In recent years,people take advantage of lactic acid bacteria have many nutritional value to carry out the research on the reduction and transformation of selenite to form organic selenium or selenium nanoparticles as a biological carrier.In this study,a strain?Lactobacillus paralimentarius?JZ07 with higher tolerance to selenite stress and also higher ability of Selenium accumulation and transformation was investigated.The characteristics of Se-enriched and transformation were studied.Then,the accumulation and species distribution of selenium in Se-enriched bacterial cells of the strain were analysis.The product of reduction and transformation of selenite was identified and characterized.This study will provide theoretical support for the study of biotransformation of inorganic selenium and supplementation of beneficial and inexpensive selenium sources for humans and animals.The biomass and ability of the selenium-enriched in lactic acid bacteria were determined by nephelometry and 3,3'-diaminobenzidine colorimetry.The results showed that JZ07 has higher tolerance to selenite stress and also higher ability of Selenium accumulation and transformation.The characteristics of Se-enriched of strain JZ07 under different culture conditions were studied.The results showed that the Se-enriched capacity was highest when the culture temperature was 37°C,the initial pH was about 6,and the amount of broth added was 5%.Accumulation and species distribution of selenium in Se-enriched bacterial cells of the JZ07 were determined by hydride generation atomic fluorescence spectrometry?HG-AFS?.The results showed that the selenium content in the lyophilized cell biomass of strain JZ07increased from 121±16?g/g to 1408±56?g/g,and could absorb 1.3-2.0%of inorganic selenium in the medium and transform most of it into organic selenium,which accounted for11.4-28.0%of total absorbed selenium.Most of the organic selenium?5.9-61.1%?was found in the protein fraction,followed by the nucleic acid and the least in the polysaccharide.Furthermore,the selenium content of different protein extractions was in the following order:Alkali-soluble protein bound selenium?5.3-78.5?g/g?>Water soluble protein free selenium?4.3-60?g/g?>Salt-soluble protein bound selenium?5.8-52.7?g/g?>Alcohol-soluble protein bound selenium?not detected?.Sodium dodecyl sulfate-polyacrylamide gel electrophoresis?SDS-PAGE?observed that there were major protein bands such as 11,18,34,41,64,and95kDa in the electrophoretogram of strain JZ07.The molecular weight of the protein is in the range of 11-100kDa,and the protein band of protein or protein subunits with the molecular weight of 11-23kDa has the highest selenium content,reaching about 0.284?g/g.Amino acid content determination results displayed that selenium increases most amino acid content of JZ07 samples.The increase in methionine?Met?content was particularly noticeable,from0.175±0.019mg to 0.213±0.094mg.The product morphology of selenite reduction and transformation by JZ07 was identify-ed by Transmission Electron Microscopy?TEM?.A large amount of irregular,nano-sized,spherical particle deposits around the selenium-rich strain JZ07 cell wall were observed in TEM images.These deposits were characterized using field Scanning Electron Microscopy?SEM?and Energy Dispersive X-Ray Spectroscopy?EDX?.It was found that these sediments are selenite particles of about 59.6-183.5 nm.Then the X-ray Diffraction?XRD?and Raman Spectra analysis confirmed that these selenium particles are insoluble,electronically dense,amorphous and amorphous??-Se?nano-selenium particles.The purity and composition of the reduced conversion selenite product of strain JZ07 was further characterized by X-ray Photoelectron Spectroscopy?XPS?and Fourier Transform Infrared Spectroscopy?FTIR?and the results indicated that the protein may play a role in the formation of selenium nanoparticles.