Fluorescence microscopy of <i>E</i>. <i>coli</i> agar biofilms.

Light microscopy images, fluorescence microscopy images, and overlay images of four different strains stained with FSB and CR are shown. The strains studied are: MC4100, MC4100Δcsg, UTI89, and UTI89ΔcsgA. MC4100 is a laboratory E.coli strain that produces curli as its only extracellular feature, and MC4100Δcsg is the isogenic curli-knockout strain. UTI89 is a commonly studied UPEC strain that produces both curli and phosphoethanolamine-modified cellulose extracellularly, and UTI89ΔcsgA is the isogenic csgA-knockout strain. (A) FSB stained only curli-producing bacteria (MC4100 and UTI89). (B) CR also binds to cellulose and is not specific for curli. This is evident as CR stained MC4100 and UTI89 as well as UTI89ΔcsgA, which only produces extracellular cellulose but not curli. MC4100Δcsg does not produce either curli or cellulose, and it was not stained by either FSB or CR. Representative images from three experiments are shown. The scale bars represent 20 μm.