Uptake of Nickel from Industrial Wastewater by Genetically Engineered Escherichia coli JM109

Abstract

[中文文摘]利用通过基因工程技术所构建的在细胞内同时表达出高特异性镍转运蛋白和金属硫蛋白的基因工程菌富集水体中的镍离子。菌体细胞对Ni2 + 的富集速率很快 ,富集过程满足Langmuir等温线模型。与原始宿主菌相比 ,经基因改造的基因工程菌不仅最大镍富集容量增加了 5倍多 ,而且对pH值、离子强度的变化及其它共存重金属离子的影响都呈现出更强的适应性。相比而言 ,Na+ 、Ca2 + 、Cd2 + 、Pb2 + 的影响较小 ,但Mg2 + 、Hg2 + 和Cu2 + 所引起的负面效应较大。进一步的实验表明基因工程菌对Ni2 + 的富集行为不需要外加营养物质。[英文文摘]　Heavy metal wastewater poses a serious threat to the environment . In comparison to the existing methods of chemical precipitation , ion exchange and carbon adsorption , biosorption is an attractive alternative for the recovery of heavy metals from industrial effluents. However , nickel ion , different fromother heavy metal ions , is a more recalcitrant pollutant and has low affinity to many metal tolerant microorganisms. In this study , Escherichia coli JM109 was genetically engineered to simultaneously express a Ni2 + transport system (the product of nixA gene) andoverexpress metallothionein (MT) . NixA protein has a high affinity for Ni2 + , and metallothioneins (MTs) are capable of binding a variety of heavy metals including Ni2 + . The Ni2 + bioaccumulation performance of the genetically engineered E. coli JM109 was evaluated. Time2course test showed that the bioaccumulation rate was rapid , and 95% of the accumulation was achieved within the first 10 minutes. The maximum Ni2 + bioaccumulation by genetically engineered E. coli cells was dramatically increased from 1154mgPg to 10111mgPg , a more than fivefold increase than that of the original E. coli strain. The isothermwas of Langmuir type. Within the tested pH range (pH 4～10) , the engineered cells displayed more resistance to pH variation , retaining up to 80 %of the Ni2 + binding capacity at pH4 , while the original E. coli host cells lost 80 % of Ni2 + binding capacity at pH 4. The presence of Na + and Ca2 + affected Ni2 + bioaccumulation, but the effects were not serious , as 71% and 66% of the Ni2 + binding capacities were retained respectively at the concentrations of 1000mgPL Na + and 1000mgPL Ca2 + . However, Mg2 + exerted a severe adverse effect on Ni2 + bioaccumulation ,83% of Ni2 + accumulating capacity was lost when Mg2 + concentration reached 200mgPL. The effects of different kinds of heavy metals on Ni2 + accumulating were different . The genetically engineered E. coli cell lost less than 45% of its Ni2 + bioaccumulation activity in the presence of 50mgPL lead or cadmium, 66% in the presence of 25mgPL mercury and 84% in the presence of 40mgPL copper. The presence of glucose did not improve Ni2 + uptake. Our study suggests that the genetically engineered E.coli JM109 has potential application for effective and efficient recovery of nickel from aqueous solutions.教育部留学回国人员启动基金资