Analysis of the mitigation of heavy metal toxicity by metallothionein from the Pacific abalone, Haliotis discus hannai

Abstract

Metallothioneins (MTs) are cysteine-rich proteins that are crucial to the binding and detoxification of heavy metals in various organisms. To study the functional role of MT in the Pacific abalone, Haliotis discus hannai, recombinant MT (rHdhMT) was expressed in Escherichia coli and purified using affinity chromatography. We analyzed the effects of rHdhMT on heavy-metal- induced bacterial aggregation, cytotoxicity, and heavy-metal bioaccumulation. Fluorescence-microscopy analysis revealed that rHdhMT reduced the aggregation of Bacillus subtilis induced by high concentrations of Zn and Cu. An ultrasensitive radial diffusion assay demonstrated that rHdhMT reduced the toxic effects of heavy metals on bacteria. This result was supported by increased survival of E. coli cells expressing rHdhMT on plates containing high concentrations of Zn and Cu. Inductively coupled plasma assays further demonstrated the heavy-metal binding effect of MT, with results showing increased accumulations of Zn and Cu in E. coli cells expressing rHdhMT. These findings provide evidence of the heavy-metal binding capacity of rHdhMT, and imply potential applications in aquatic environmental monitoring, mitigation of biotoxicity caused by heavy metals, and biomining.