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 find more 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 FGFR inhibitor 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). buy RAD001 Finally, the cells are imaged in TIRF mode with epi-like TIRF angle. FRAP results on full-length OmpA-mCherry
As we were interested in diffusion / mobility of OmpA in the OM, and Astemizole our timescale of observation is tens of minutes, we risked mistaking OmpA synthesis, OM insertion and / or fluorophore maturation for fluorescence recovery caused by lateral diffusion. To minimize this risk we adopted the following procedure: First the cells were grown to steady state in DRu medium in the presence of IPTG to induce expression (“pulse”), followed by resuspension of the cells in medium without IPTG to repress new synthesis (“chase”). Growing the cells in DRu medium for an additional 2 hours in the absence of IPTG allows time for export to finish and the mCherry fluorophore to mature. This way, we expected to end up with cells that contain little precursor or partially degraded protein. Then we transfered the filaments to the observation chamber (DRu-agar with ampicillin and cephalexin) and performed the FRAP experiment at room temperature. We made use of the Perfect Focus System that is part of the Nikon Eclipse Ti microscope system to keep the filament in focus during the experiment, which takes about 15–20 min per filament (N = 9). In Figure 4 a representative image series is shown. Several observations can be noted. As is apparent, significant bleaching occurs (exposure time 100 ms, acquisition rate 2 frames per second (fps)).