Heterologous expression of an acidophilic multicopper oxidase in Escherichia coli and its applications in biorecovery of gold

Background: Copper oxidase is a promising enzyme for detection of oxidation, which can function as a biosensor and in bioremediation. Previous reports have revealed that the activity of the multicopper oxidase (MCO, EC 1.10.3.2) from the Proteus hauseri ZMd44 is induced by copper ions, and has evolved to participate in the mechanism of copper transfer. Results: From P. hauseri ZMd44, a full-length, 1497-base-pair gene, lacB, encoding 499 amino acids without signal peptide, was cloned into Escherichia coli (E. coli) to obtain high amounts of MCO. The use of the pET28a vector yielded better enzyme activity, which was approximately 400 and 500 U/L for the whole cell and soluble enzyme extracts, respectively. The crude enzyme showed activity at an optimal temperature of 55 °C and it remained highly active in the range of 50–65 °C. The optimal pH was 2.2 but the activity was significantly inhibited by chloride ions. This MCO has great potential for Au adsorption (i.e., 38% w/w) and the Au@NPs were directly adsorbed on enzyme’s surface. Conclusion: An acidophilic MCO from bioelectricity generating bacterium, P. hauseri, is first cloned and heterologously expressed in E. coli with high amounts and activity. This MCO has great potential for Au adsorption and can be used as a biosensor or applied to bioremediation of electronic waste.