Objective: The aim of our study was to isolate and identify merA gene from a bacterial strain with high resistance to mercury.
Methods: A bacterial strain with resistance to mercury was isolated from the river sediment of Liangshui river in Beijing. The strain was identified according to the sequence analysis of 16S rRNA gene and its physiological and biochemical properties. A pair of PCR primers was designed according to the merA gene sequences of some bacteria published in the GeneBank to amplify the complete merA gene using the genomic DNA of KHg2 as a template. The PCR-amplified DNA fragment was expressed in Escherichia coli BL21 (DE3). Mercury resistance of the expression strain was tested.
Results: A bacterial strain which could grew on LB medium plate containing 70 mg/L HgCl2 was isolated, it was named as KHg2. The strain KHg2 shares 96% sequence identity with the type strain DSM12223T of Bacillus silvestris. The morphological characteristics and the results of physiological and biochemical properties of the strain were agreement with that of Bacillus silvestris. One PCR fragment of 1680 bp was obtained from the strain, which shares 99% sequence identity with merA gene of Pseudomonas putida. The PCR-amplified DNA fragment was cloned into a pET-30a (+) vector to obtain a expression plasmid pZY2. The expression plasmid was transformed into E. coil host strain to obtain a expression strain E. coli BL21 (DE3) x pZY2, a protein of 33 kDa was expressed by the expression strain after induced with isopropyl-b-D-thiogalactoside (IPTG). The result of heavy metal resistance test showed that the expression strain could grew on LB medium containing 20 mg/L HgCl2, meanwhile a negative control, E. coli BL21 (DE3), harbouring pET-30a (+), could not grew on LB medium containing 20 mg/L HgCl2.
Conclusion: The isolated strain KHg2 was closely related to Bacillus silvestris. A merA gene was cloned from the strain KHg2 and was expressed successfully in E. coli. The expression strain E. coli BL21 (DE3) x pZY2 has resistance to heavy metal mercury.