Figure 4

Comparison of tetracycline sensor with positive feedback (solid circles) and without (solid square). Schematic of positive feedback design is shown in Figure 3. The design lacking positive feedback is otherwise identical to one with positive feedback except that only GFP is expressed from the P _luxI promoter. In these experiments, cells were grown overnight at the indicated concentrations of aTc prior to measurements. The fluorescence values were normalized with the OD₆₀₀ absorbance to account for cell density. Error bars denote 95% confidence intervals for the measurement average.