Bacterial numbers of each species in the biofilms. Numbers of each strain were counted by epifluorescence microscopy, following staining by FISH or IF. Data was plotted on a logarithmic scale. Asterisk (*) indicates significant differences (P < 0.01) between the groups. Open circle indicates data points considered as outliers. Groups are defined by the use of the corresponding P. gingivalis strain (W50; wild-type, E8; Arg-gingipain-deficient mutant, K1A; Lys-gingipain-deficient mutant).