Enhancement of chromate bioaccumulation by engineered Escherichia coli cells co‐expressing chromate reductase (YieF) and a rice metallothionein isoform (OsMT1)

Abstract

BACKGROUND Hexavalent chromium Cr(VI) is a toxic and carcinogenic heavy metal. It is highly water soluble and one of the most widely used metals in industry, resulting in soil and water contamination. Nowadays engineering microbes provide new strategies for remediation of heavy metals. RESULTS In the present work, a gene encoding E. coli chromate reductase (YieF) was cloned in pCDF‐1b and was transferred to both cells containing empty pET41a (control strain), and cells containing pET41a‐OsMT1 (R‐MT1) resulted in production of new strains R‐YieF and R‐YieF/MT1, respectively. Both proteins – YieF as His‐tag fusion protein and OsMT1 as glutathione‐S‐transferase fusion protein – appeared in the soluble fraction of R‐YieF/MT1 after induction with isopropyl‐d‐1‐thiogalactopyranoside . The strain R‐YieF/OsMT1 showed high tolerance to Cr6+ and accumulated significantly higher Cr6+ than R‐MT1 (5 mg L−1), R‐YieF (7 mg L−1) and control (2 mg L−1). The accumulation of Cr6+ was dependent on the initial concentration of Cr6+ in the medium, time and the presence of other toxic metals such as Ag+1, Hg+2 and Cd2+. CONCLUSION This study demonstrated that the co‐expression of YieF and OsMT1 could effectively enhance the accumulation of Cr(VI) by E. coli cells and opens new insights into bioremediation strategies. © 2020 Society of Chemical Industry