Figure 3.

(a) Demonstration of a three-color sensor. At very low zinc, the cells produce substantial violacein and lycopene. At increasing concentrations of zinc, violacein production is repressed and the sensor is in a primarily lycopene state. As zinc increases further, lycopene is consumed and cells enter a primarily β-carotene state. (b) Cell pellets from the experiment in panel a. (c) Fluorescent reporter output in test with 32 decoy Zur operators and inducible Zur. Asterisks indicate significance at p < 0.05. (d) Violacein extract levels from decoy Zur operator test and varying RBS strength on inducible Zur. A construct without a decoy array or inducible Zur is presented for comparison (blue). Double asterisks denote statistical significance (p < 0.05) between red and blue. Single asterisks denote statistical significance between gray and blue (p < 0.05). Error bars indicate standard deviation.