Deng Xu, Li Qing-Biao, Lu Ying-Hua, Sun Dao-Hua, Huang Yi-Li
Department of Chemical Engineering, Xiamen University, Xiamen 361005, China.
Sheng Wu Gong Cheng Xue Bao. 2003 May;19(3):343-8.
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 from other 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. Time-course 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 1.54 mg/g to 10.11mg/g, a more than five-fold increase than that of the original E. coli strain. The isotherm was 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 pH 4, 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 1000 mg/L Na+ and 1000 mg/L Ca2+ . However, Mg2+ exerted a severe adverse effect on Ni2+ bioaccumulation, 83% of Ni2+ accumulating capacity was lost when Mg2+ concentration reached 200 mg/L. 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 50 mg/L lead or cadmium, 66% in the presence of 25mg/L mercury and 84% in the presence of 40 mg/L 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.
重金属废水对环境构成严重威胁。与现有的化学沉淀、离子交换和碳吸附方法相比，生物吸附是从工业废水中回收重金属的一种有吸引力的替代方法。然而，镍离子与其他重金属离子不同，是一种更难处理的污染物，对许多耐金属微生物的亲和力较低。在本研究中，对大肠杆菌JM109进行基因工程改造，使其同时表达Ni2+转运系统（nixA基因的产物）并过表达金属硫蛋白（MT）。NixA蛋白对Ni2+具有高亲和力，而金属硫蛋白（MTs）能够结合包括Ni2+在内的多种重金属。对基因工程改造的大肠杆菌JM109的Ni2+生物积累性能进行了评估。时间进程测试表明，生物积累速率很快，在最初的10分钟内实现了95%的积累。基因工程改造的大肠杆菌细胞对Ni2+的最大生物积累量从1.54 mg/g显著增加到10.11mg/g，比原始大肠杆菌菌株增加了五倍多。等温线为朗缪尔型。在测试的pH范围（pH 4-10）内，工程细胞对pH变化表现出更大的抗性，在pH 4时保留高达80%的Ni2+结合能力，而原始大肠杆菌宿主细胞在pH 4时失去80%的Ni2+结合能力。Na+和Ca2+的存在影响Ni2+生物积累，但影响不严重，在1000 mg/L Na+和1000 mg/L Ca2+浓度下分别保留了71%和66%的Ni2+结合能力。然而，Mg2+对Ni2+生物积累产生严重不利影响，当Mg2+浓度达到200 mg/L时，83%的Ni2+积累能力丧失。不同种类的重金属对Ni2+积累的影响不同。在存在50 mg/L铅或镉的情况下，基因工程改造的大肠杆菌细胞失去的Ni2+生物积累活性不到45%，在存在25mg/L汞的情况下为66%，在存在40 mg/L铜的情况下为84%。葡萄糖的存在并未提高Ni2+的摄取。我们的研究表明，基因工程改造的大肠杆菌JM109在从水溶液中有效且高效地回收镍方面具有潜在应用价值。
