Figure 2. P_BAD-msfGFP.

(a) Design of P_BAD-msfGFP strain. (b) Unlike a typical inducible promoter with a bimodal “on/off” switch-like behavior, expression by P_BAD in this modified strain shows a gamma distribution²⁷,³⁰ (filled circles = data, line = gamma distribution fit). Each gamma distribution represents an independent arabinose concentration trial. As the expression level becomes high, the distribution of msfGFP per cell volume becomes more symmetric and approaches Gaussian. The arabinose concentrations correspond to the ones used in (c). (c) The dynamic range of P_BAD in this strain is more than 100-fold (filled circles = data, line = dose-response sigmoid curve; error bars = standard deviations). (inset) Data in log-log scale. (d) Response of P_BAD is fast and reversible. (Inset) The first five data points from wash in semi-log scale (t = 0 is when arabinose is removed). The line is an exponential fit, demonstrating an immediate exponential dilution of msfGFP by growth upon removal of arabinose induction. Filled circle = No induction, open circle = induction at [arabinose] = 0.1%.