Figure 2.

PFM of freely diffusing GFP in bacterial cells. (A) Side view of E. coli cells expressing free GFP (213 cells included). As the angle between the cell axis and the lab axis, α, changes, the images show an intrinsic polarization anisotropy. The reason for this is unclear; it is likely the result of birefringence of biomaterials such as the peptidoglycan cell wall. The results can be used to derive an anisotropy factor, C, which can be used to correct the intensity from fluorophores attached to FtsZ (see text and Supporting Material). (B) C. crescentus cells with freely diffusing YFP show a similar intrinsic anisotropy (133 cells included). To see this figure in color, go online.