Study On Mechanism Of Mercury Methylation By Sulfate-reducing Bacteria

Mercury is a natural heavy metal element in the environment,with biological toxicity,persistence and enrichment.Gaseous elemental mercury can be transported over a long distance with the atmospheric circulation,and has been defined as a global pollutant.Different forms of mercury compounds can be converted to each other under suitable environmental conditions,among which the conversion of inorganic mercury to methyl mercury is the mostly concerned process.At present,sulfate-reducing bacteria,iron-reducing bacteria and methanogens are considered to be the main mercury methylation microorganisms in the environment.However,the sulfate reducing bacterium D.desulfuricans ND132 belongs to Gilmour laboratory and is not a commercial strain.Its use and related research should be applied for and licensed by Gilmour laboratory.This barrier makes it difficult to standardize and use the research methods.For many domestic laboratories,it is hard to carry out research on microbial mercury methylation by D.desulfuricans ND132.This paper collected seven kinds of sulfate-reducing bacteria from the Chinese general microbiology preservation management center and other laborator.Under pure culture conditions mercury methylation key genes(hgcA and hgcB),growth characteristics,mercury tolerance and mercury methylation ability were systematicly investigated,as well as a preliminary screening of suitable mercury methylation patterns.The results showed that Desulfomicrobium escambiense(CGMCC 1.3481)have a conversion rate(of up to 7.5%±0.7%)under an optimized condition,indicating that it could serve as an model strain for study on mercuric methylation with SRB.In order to further investigate the methylation process and pathway of Hg,we investigated the differential expression of Desulfomicrobium escambiense(CGMCC 1.3481)in Hg methylation by proteomics.After Isobaric tags for relative and absolute quantitation(iTRAQ)was labeled,Liquid chromatography-tandem mass spectrometry(LC-MS/MS)was used for identification and quantitative analysis.The mass spectrometry data were analyzed by software Mascot 2.5 and ProteomeDiscoverer 2.1,and the Gene Ontology(GO)functional annotation and KEGG(Kyoto Encyclopedia of Genes and Genomes)pathway analysis were performed on the differentially expressed proteins.The results showed that 28 proteins met the screening criteria of differential protein FC>1.2 or <0.83,and p<0.05,including 27 up-regulated proteins and 1 down-regulated protein.Desulfomicrobium escambiense may have the same acetyl-coenzyme A pathway in the methylation of mercury as Desulfovibro desulfuricans ND132.