Using engineered microorganisms to detect heavy metals in the environment has proven to be highly effective and robust. This paper reports on the development of a novel microbial sensor for the detection of copper ions. To develop this microbial sensor, we screened and characterized various biological parts, including promoters, output signals, and hosts. In addition, we used the plant pigment betaxanthin to output fluorescent signals in order to reduce the detection time. The resulting whole-cell biosensor presented a good sensitivity when detecting copper ions in environmental samples including freshwater pond and tap water.Metal ions including iron, copper, zinc, and manganese play important roles as cofactors for enzymes involved in the catalysis of metabolic processes, and the maintenance of cell integrity, which is achieved through regulation by osmotic pressure.1,2 These ions are ubiquitous in all organisms; however, heavy metals can be toxic at high intracellular concentrations.3,4 For example, an excess of copper ions can cause protein dysfunction by interacting strongly with thiol groups and interfere with assembled ironsulfur cofactors.5 This has led many microorganisms to develop the ability to sense small variations in metal concentrations as well as the means to control the inux and efflux of metal ions.

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Despite the importance of 2-phenylacetic acid, a plant hormone in the endogenous auxin family, its biosynthesis pathway has yet to be elucidated. In this study, we developed a novel whole-cell biosensor for the simultaneous quantification of 2-phenylacetic acid (PA) and 2-phenylethylamine (PEA) through the regulation of bacterial catabolism of aromatic compounds. We used the PA regulon to enable the recognition of PA and PEA. Differentiation of PEA from PA involves the incorporation of the FeaR regulon within the same whole-cell biosensor to report the presence of aromatic amines. The proposed system is highly sensitive to PA as well as PEA.