Fig 8.

Propidium iodide (PI) staining of P. aeruginosa colony biofilms, Each strain constitutively expressed the GFP from plasmid pMF230 for visualization of the colonies. Cells were stained by placing colony biofilms on filters containing PI for 30 min, as described in Materials and Methods. Biofilms were imaged following cryoembedding and thin sectioning. (A) Very little PI staining was observed for P. aeruginosa PAO1. (B) The P. aeruginosa Δrmf strain consistently showed a band of red fluorescence, indicative of PI uptake, along the bottom of the biofilm. The P. aeruginosa ΔPA4463 strain had variable levels of staining but generally did not stain with PI. PI uptake is often used to indicate cells with compromised cell membranes.