Chromium Resistance Characteristics Of Chromium (VI) Resistance Genes ChrA1 And ChrB In Serratia Sp.S2

objective:Chromium(VI)transporter-protein-coding gene A,B,AB in Serratia sp.S2 are cloned,and their prokaryotic expression vectors were constructed and transformed into E.coli BL21.The role of ChrA1 and ChrB genes in the chromium resistance and the mechanism of chromium metabolism were investigated by studying the anti-chromium ability and characteristics of engineered bacteria.Method:The PCR technique was used to amplify ChrA,ChrB,and ChrAB genes from the Serratia sp.S2 genome.ChrA1,B,A1B genes were connected to the prokaryotic expression vector pET-28a(+),and transferred into E.coli BL21 for prokaryotic expression to construct the engineered bacteria.The function of ChrA1 and ChrB was determined by measuring the growth curve,the absorption of chromium and the chromium efflux.To explore the effects of chromium(VI)loading time,respiratory inhibitor(valeromycin,oligomycin,CN-,NADH)and oxygen-containing anions(sulfate,molybdate,vanadate,tungstate)on chromium efflux of engineered bacteria,and to analyze the mechanism of ChrA1 and ChrB protein chromium transport.Result:ChrA1,ChrB and ChrA1B engineered bacteria were constructed successfully through DNA recombinant technique.The ChrA1 and ChrA1B engineered strains had stronger chromium risistance than the control strian[pET-28a(+)in E.coli BL21],which significantly decreased the absorption of chromium(P<0.05),increased the chromium efflux rate(P<0.05),while there was no significant difference between the ChrB engineered strain and control strain for Cr(VI)-resistance ability(P>0.05).The efflux rate of ChrA1 and ChrA1B engineered strains decreased with the prolongation of Cr(VI)loading time,and also cloud be inhibited significantly by oxyanions sulfate and molybdate(P<0.05).In the respiratory inhibitor,K~+vector of valinomycin and CN significantly inhibited the efflux of Cr,while NADH can promote its Cr efflux(P<0.05).Conclusion:The expression of ChrA1 can improve the Ecoli BL21 of Cr(VI)resistance;ChrA1 gene coded chromium transporter use proton power to pump chromium ions out of cells through the chemical permeation of cell membrane.The ChrB gene plays a positive regulatory role in ChrA1 gene regulation to make ChrA1B engineered strain stronger than ChrA1 engineered strain on ability of chromium resistance and efflux.