Reduction And Mechanism Of Cr(?) By Klebsiella Z3

With the rapid development of industry,a large amount of chromium-containing wastewater was discharged into the water and caused serious harm to the environment.Cr(?)was highly toxic,it was internationally recognized as one of the carcinogens,therefore,the management of chromium pollution was a major issue in the field of environmental protection.Compared with the traditional physical and chemistry method,microbial treatment had the advantages of low cost of treatment,friendly environment,simple operation and has wide application prospect in the treatment of chromium-containing wastewater.In this study,a strain capable of efficiently reducing Cr(?) was screened from soil contaminated by pesticides.Based on biochemical characteristics,16 S r RNA sequence and phylogenetic analysis,the strain was identified as Klebsiella,named Z3.Cr(?)reduction experiments showed that Z3 was a aerobic bacteria,with basophilic and salt-resistant properties.The optimum temperature for Cr(?)reduction was 36 ? and the optimum p H was 9.12.The kinetic analysis of Cr(?)reduction showed that the reduction of Cr(?)by Z3 was a zero-order reaction under the resting condition and was a first-order reaction when in the growth condition.In order to investigated the reduction mechanism of Cr(?) by Klebsiella Z3,we used scanning electron microscopy,gradient ultracentrifugation and EDS studed the morphological changes under Cr(?)stress,the Cr(?)reduction ability of different cellular components,distribution of chromium in the subcellular and the reduction position of Cr(?)in the cell.At the same time,the elemental composition of Cr(?)reduction precipitates was qualitatively analyzed by XPS.The results showed that Z3 mainly through the way of extracellular reduction to remove the Cr(?).During the process,the soluble Cr(?)was reduced to a lower water-soluble trivalent chromium precipitate and the extracellular polymer was the main Cr(?)reduction position in the cells,which played a very important role in the Cr(?)reduction process.The SEM results showed that the bacterial cells could secrete large amounts of extracellular polymers under Cr(?)stress conditions.The results of the distribution of chromium in the cell subcellular showed that the majority of the Cr remained in the culture solution,and only quite a few were immobilized in the bacterial cell(10.8%~14.4%),extracellular polymer(85.6% ~ 89.2%)and cytoplasm(11.5% ~ 21.2%)were the main distribution sites in cells,only a small amount of chromium was distributed in the cell wall(6.5%~12.8%)and cell membrane(3.5%~10.4%).The reduction of Cr(?)by cell components showed that EPS was of vital importance for the Cr(?)tolerance,and was the main Cr(?)reduction site.The Cr(?)reduction capacity of cellular components from high to low as EPS> cytoplasm> cell membrane> cell wall.The results of EDS analysis revealed that precipitation of Cr(III)in the reduction process was mainly located in the culture medium and there was no Cr(III)present in the cells.XPS results showed that the bacterial cells mainly reduced the soluble Cr(?)to the less water-soluble Cr(OH)3 and then to achieved the purpose of removing Cr(?).An effective and comprehensive method,2-DE combining with MALDI-TOF/TOF,was used to study the differential proteins induced by Cr(?).About 600 proteins were separated by 2-DE.23 protein spots of which were excised from the gels to identify by MALDI-TOF/TOF.Taking into account their main biological functions,these proteins were classified into seven different functional groups as Protein synthesis,energy metabolism,amino acid metabolism,stress response,immune response,signal transduction and fatty acid metabolism.