Figure 3. Tuning of pyoverdine expression in response to iron availability and time.

(A) Population-level median GFP expression over time for the pvdA-gfp reporter (red lines) and a control strain constitutively expressing GFP (grey lines) under different iron supplementation regimes (circles = 0 µM iron added, squares = 5 µM iron added, diamonds = 20 µM iron added). The blue line depicts background fluorescence signal of the wildtype PAO1 strain without reporter. (B) shows the distributions of individual-level GFP expression of the pvdA-gfp reporter (red), the constitutive gfp reporter (grey), and the wildtype control (blue) for the 0 µM and 5 µM iron supplementation regimes, respectively. While the data indicate that the absolute level of pyoverdine expression is extremely fine-tuned in response to iron availability and over time, in all cases the observed values are clearly unimodally distributed.