Genome Sequence Analysis Of Serratia Sp. S2 And Characteristics Of Hexavalent Chromium Reduction Of Chromate Reductase Chrt Engineered Bacteria

Objective: To analyse the genome sequence of Serratia sp. S2 and possible mechanism of removing hexavalent chromium. Study the Cr(Ⅵ) reducing capacity and impact factors of chromium reductase ChrT engineered bacteria, and to analyse of the activity of chromium reductase ChrT. After passage cultivation, observe and detect the stability of biological characteristics of chromium reductase ChrT engineered bacteria.Methods: The genome sequence of S2 was determinated, then related genes of removing hexavalent chromium were analysed and possible mechanisms were discussed. The ability of hexavalent chromium reduction was compared among ChrT engineered bacteria, Serratia sp. S2 and host bacteria E.coli BL21(DE3), then the effects of culture condition(p H, temperature, carbon sources and metal ions) on the Cr(Ⅵ) removal efficiency of ChrT engineered bacteria were explored. After IPTG induction, the activity of the chromate reductase ChrT was determined by the enzymatic reaction. The engineered bacteria was subcultured for 50 passages, and subjected to chromium reduction test, Gram staining and biochemical examination as well as test for expression level of target protein and property of plasmid in every 10 passages.Results: Genetic sequence of S2 was got by gene sequencing and its total size was 5,604,115 bp. It contained 12 gene which related to chromate transporter and chromium reductase. After cultured 48 hours, the Cr(Ⅵ) reduction rate of the engineered bacteria was up to 40% while the initial Cr(Ⅵ) concentration of medium was 50mg/L. The optimum culture condition was pH 7.0 and 37℃. Sodium lactate, sodium acetate, Cu2+, Co2+, and Pb2+ can positively improve the Cr(Ⅵ) reduction ability of ChrT engineered bacteria. After IPTG induction, the enzyme activity of ChrT was up to 14.7 U/mg when NADPH was used as electron provider. The colonial morphologies, gene sequences and the expression levels of chromate reductase of various passages had no obvious difference. All the passages were negative in Gram staining and showed typical characteristics of E. coli in biochemical examination. The Cr(Ⅵ) reduction rate of every 10 passage was about 40% while the initial Cr(Ⅵ) concentration of medium was 50mg/L, which showed no significant difference(p>0.05).Conclusion: Serratia sp. S2 have chromium related genes, which provided genetic resources for further studying the efficient Cr(Ⅵ)-removel engineered bacteria. The ChrT engineered bacteria and ChrT reductase owned Cr(Ⅵ) reducting capacity, and showed stable biological characteristics, and might be used for remediation of chromium contaminated soil and water.