Figure 3

Rapid recovery of cytoplasmic mCherry. Filament imaged at 2 fps. Halftime of recovery is on the order of 1 s. A false color scale (ImageJ Rainbow RGB) is used to emphasize differences in intensity. A rectangular ROI box of 2 x 28 is positioned manually at the center of bleaching, and the average pixel intensity, corrected with the average background intensity is calculated. Two subsequent FRAP events are recorded, at two different locations. The two FRAP ROIs are drawn in the prebleach image. For the first FRAP pulse, the first few images are depicted in A). After each laser pulse, total fluorescence is also reduced by approx. 20% because during bleaching also the imaging continued at maximum laser power. This was corrected in subsequent experiments on OmpA (Figures 4 and 5). B) Pixel intensities after background subtraction for both the FRAP ROI (gray symbols) and a non-bleached reference ROI (red symbols) along the filament. Bacterial diameter is ~ 1 μm. Protocol: A fresh overnight culture of LMC500/pSAV047 grown in TY medium at 28°C is diluted 5000x into fresh TY medium and grown for 2 hours. Then cephalexin is added to induce filamentation and the cells are grown further for 2 hours. Next, the cells are concentrated 10x by centrifugation and resuspension. Then 2x 5 μl cells are added to a glass observation chamber containing TY agar with cephalexin and ampicillin (10 μg/ml and 100 μg/ml respectively). Finally, the cells are imaged in TIRF mode with epi-like TIRF angle.