Study On Polyphasic Taxonomy Identification Of Novel Species Of Selenite Reduced Lysobacter And Selenite Resistance Mechanism

Selenium is an essential trace element for living organisms and is widely used in industry,agriculture and medicine.Excessive intake can cause poisoning in humans,animals and plants.Selenium has variable valence states（-II,0,+IV and+VI）,with Se（IV）and Se（VI）being the most toxic,damaging cell structure,causing oxidative damage to DNA,leading to genetic mutations and tumour development.Emissions from industrial production,agricultural activities,mineral extraction,coal burning and glass manufacturing waste can lead to excessive levels of selenium in the environment and exacerbate environmental hazards."There is no substitute for ecology,it is hard to use it and hard to lose it".While controlling and eliminating the source of pollution,research and development of environmental pollution remediation technology with high efficiency,green and cheap is particularly significant for China,where resource conservation and environmental protection are the basic national policies and sustainable development is established as a national strategy.Microbial remediation of environmental pollution has the advantages of being environmentally friendly,economical and sustainable,and is a hot spot for research in the field of pollution remediation.A variety of microorganisms capable of reducing selenium compounds have been identified,and the reduction product bio-nano-monolithic selenium has a wide range of applications and great potential.River bottoms are unique ecological environments and areas for precipitation,adsorption and aggregation of complex pollutants,promising the screening of potential new species with specific metabolic and adaptive capabilities.In this study,a potential novel strain of Lysobactyer with sodium selenite[Se（IV）]resistance and reduction capacity,strain 13A^T,was screened from the river bottom mud of the Bushyang River in Hebei,focusing on the multiphase taxonomic identification of novel Se（IV）resistant/reducing species,the phenotypic mechanistic characterization of reduced Se（IV）to produce bio-nano-monolithic selenium,and the comparative genomic analysis of Se（IV）resistance and reduction-related The work was carried out in three areas:functional genes and potential mechanisms related to Se（IV）resistance and reduction,as well as a review of selenium resistance/reduction microbial resources,mechanisms of selenium resistance/reduction by microorganisms and the current status of applications of microbial-derived singlet selenium nanomaterials.The main findings are as follows:1.Polyphasic taxonomy identification study of selenium-reducing Lysobacter selenitireducens:80 strains of 18 genera were isolated and screened from samples from the Bushy River,Hebei.The 16S r RNA similarity between strain 13A^Tand the known standard strains was highest with Lysobacter spongiicola DSM 21749^T（97.8%）,which was below the threshold of 98.7%for novel species determination,and it was hypothesized that strain 13A^Tmight be a potential new species of Lysobacter.Polyphasic taxonomy identification of strain 13A^Twas carried out,and strain 13A^Twas finally identified as a new species of the genus Lysobacter,and a new species name Lysobacter selenitireducens13A^Twas proposed at the international level.2.Phenotypic mechanism of Se（IV）reduction by strain 13A^T:The growth and p H changes of strain 13A^Twere determined under different Se（IV）stress conditions;the MIC value of Se（IV）was determined to be about 160 m M,and the selenium reduction rate of strain 13A^Twas determined by Na₂S chromogenic method.The reduction rate was 34.5%after 2 d of incubation.SEM-EDS,TEM and FT-IR characterisation under Se（IV）induction conditions showed that the selenium reduction by strain 13A^Tproduced spherical particles（140–300 nm）of uniform size with extracellular and intracellular distribution;functional groups such as-NH₂,-COOH and-OH in the cell surface biomolecules were involved in the reduction of selenium nanoparticles.The functional groups such as-NH₂,-COOH and-OH in the cell surface biomolecules may play a role in adsorption and aggregation during the reduction of selenium nanoparticles.3.Study of functional genes and potential mechanisms related to Se（IV）resistance/reduction:The genome of strain 13A^Twas quality-controlled,sequenced,assembled and analysed,and the sequenced and assembled genome was of good quality.The genomic information of strain 13A^Twas annotated by uploading database and the selenium-reducing protein pathway of strain 13A^Twas predicted by KEGG,which encodes10 proteases includingγ-glutamyl transpeptidase.By Venn analysis,two Se（IV）reduction pathways mediated by nitrite reductase and glutathione（GSH）in strain 13A^Twere hypothesized to be distinct from those of the reference bacteria.This study enriches the new species resources of Se（IV）-resistant/reducing bacterial species and helps to provide theoretical support and methodological basis for the study of functional genes and molecular mechanisms related to Se（IV）resistance/reduction.In addition,the reduction and transformation of highly toxic Se（IV）compounds by microorganisms into multifunctional bio-nano-monolithic selenium materials has broad application potential and development prospects in the field of bioremediation of Se（IV）pollution.