Metabolic engineering of the carotenoid biosynthetic pathway toward a specific and sensitive inorganic mercury biosensor

Abstract

The toxicity of mercury (Hg) mainly depends on its form. Whole-cell biosensors respond selectively to toxic Hg(ii), efficiently transformed by environmental microbes into methylmercury, a highly toxic form that builds up in aquatic animals. Metabolically engineered <i>Escherichia coli</i> (<i>E. coli</i>) have successfully produced rainbow colorants. By <i>de novo</i> reconstruction of the carotenoid synthetic pathway, the Hg(ii)-responsive production of lycopene and β-carotene enabled programmed <i>E. coli</i> to potentially become an optical biosensor for the qualitative and quantitative detection of ecotoxic Hg(ii). The red color of the lycopene-based biosensor cell pellet was visible upon exposure to 49 nM Hg(ii) and above. The orange β-carotene-based biosensor responded to a simple colorimetric assay as low as 12 nM Hg(ii). A linear response was observed at Hg(ii) concentrations ranging from 12 to 195 nM. Importantly, high specificity and good anti-interference capability suggested that metabolic engineering of the carotenoid biosynthesis was an alternative to developing a visual platform for the rapid analysis of the concentration and toxicity of Hg(ii) in environmentally polluted water.