Homotypic biofilm formation by P. gingivalis wild-type strain and mutants in PBS. P. gingivalis strains were stained with CFSE (green) and incubated in PBS for 24 hours. After washing, the biofilms that developed on the coverglass were observed with a CLSM equipped with a 40× objective. Optical sections were obtained along the z axis at 0.7-μm intervals, and images of the x-y and x-z planes were reconstructed with an imaging software as described in the text. Upper panels indicate z stacks of the x-y sections. Lower panels are x-z sections. P. gingivalis strains used in this assay are listed in Table 4. The experiment was repeated independently three times with each strain in triplicate. Representative images are shown.