Figure 2.

Single-molecule fluorescence detection inside living bacteria. (A) A genetic construct occasionally produces a rare protein fusion that localizes on the inner bacterial membrane, which slows down its diffusion and allows detection as a diffraction-limited spot. (B) Differential interference contrast and fluorescence images of two bacterial cells show the presence of two fluorescence spots above the autofluorescence background; these spots correspond to single YFP molecules. (C) A time-series analysis of protein expression at the single-molecule level is shown. Each protein expression event persists for a significant time, likely because of the rate-limiting steps of fluorescence development in the YFP fluorophore. The figure is adapted from (23). To see this figure in color, go online.