Quantifying mCherry Fluorescence in E. coli

The fluorescence intensity of mCherry produced in E. coli was measured as previously described (Hui et al., 2018c (link)). Briefly, E. coli cells were collected, washed, and resuspended in 50 mM PBS. A 3-mL aliquot of E. coli suspension or diluent was added to 1-cm low fluorescence background quartz cuvette. To test the fluorescence intensity of induced mCherry, the excitation wavelength was set at 587 nm and the intensity of emitted fluorescence of mCherry at 610 nm was recorded with Lumina fluorescence spectrometer (Thermo Fisher Scientific, United States). The fluorescence intensity was normalized by dividing the fluorescence intensity at the emission wavelength 610 nm by the OD₆₀₀ value of the same sample. The background value was obtained from the control assays with uninduced cell suspensions.