Bioaugmentation Treatment Of Cd(Ⅱ) In High-Salinity Wastewater By Engineered E. Coli(EC20/irrE)

The composition of high-salinity wastewater is complex,including chloride,sulfide,and heavy metals(HMs),etc.It mainly comes from the tanning,electroplating,and chemical industries.Direct discharge will cause serious pollution of the soil and water.Cd(Ⅱ)is one of the most toxic HM pollutants.Due to its undegradability and toxicity,the study on the removal of Cd(Ⅱ)from high-salinity wastewater is of great significance.Activated sludge is a low-cost biological method for the treatment of high-salinity Cd(Ⅱ)wastewater.Bioaugmentation is a promising approach to solving the practical problems of sewage treatment plants and improving the efficiency of pollutant removal.Therefore,based on synthetic biology,engineering Escherichia coli(EC20/irrE)that could adsorb Cd(Ⅱ)from high-salinity wastewater was constructed.Firstly,the salt tolerance and Cd(Ⅱ)adsorption capacity of E.coli(EC20/irrE)were investigated,and then the mechanism of irrE improving the salt tolerance of E.coli was investigated.On this basis,bioaugmentated sequencing batch reactors(SBRs)were constructed to analyze the removal efficiency of pollutants in the petrochemical wastewater.The fusion protein INP-EC20 was successfully anchored on the cell surface,and irrE was successfully expressed in the cytoplasm.E.coli(EC20)could adsorb Cd(Ⅱ),and E.coli(irrE)could survive in < 3% Na Cl,but both were inhibited in the presence of high concentrations of Na Cl and Cd(Ⅱ).While E.coli(EC20/irrE)could survive better in high salinity conditions and adsorb Cd(Ⅱ).E.coli(EC20/irrE)achieved a 95% removal rate of 23.1 mg/L Cd(Ⅱ)in 540 min,and adsorption nearly reached equilibrium when the biomass was contacted with Cd(Ⅱ)for 180 min.Adsorption kinetics was best-fitted to the Elovich model,and adsorption isotherm was best described by the Redlich-Peterson model.The adsorption of E.coli(EC20/irrE)of Cd(Ⅱ)increased with the increasing of initial concentration in the range of 3.1-92.5 mg/L,reaching 52.44 ± 0.95 mg/g under 92.5 mg/L in 180 min.Transcriptome analysis revealed that the expression of irrE in E.coli significantly improved its salt tolerance,and irrE regulated salt tolerance in E.coli through several different pathways.The changes in genes related to the production and degradation of trehalose and exopolysaccharides were consistent with the actual production.The results showed that the chemical oxygen demand(COD)and Cd(Ⅱ)removal reached up to 96.17% and 97.60%,higher than the control group(CK)of79.15% and 92.09%,under the influent COD of 1715 mg/L,Cd(Ⅱ)of 4.6 mg/L and salinity of 3.0% in bioaugmented system(BIO).16 S r RNA analysis revealed that the microbial community structure could be affected by high-salinity and Cd(Ⅱ)stress.The microbial diversity of CK and BIO was significantly reduced compared with the initial activated sludge.The extracellular polymeric substance(EPS)content of BIO was higher than CK,and the reactive oxygen species(ROS)content was lower than CK.In conclusion,engineering E.coli(EC20/irrE)was successfully constructed using the synthetic biology method,which could successfully colonize in SBR and effectively remove Cd(Ⅱ)from actual high-salinity petrochemical wastewater,providing a new idea for the treatment of such wastewater.