Grouping of T. denticola strains based on shared integron gene cassettes and their phylogenetic relationship. (A) Heat map showing the percentage of shared genes between the 14 Treponema denticola strains, with the color spectrum on the right hand side indicating the percentage. The phylogenetic tree shown on the left side of the heat map was generated based on the sharing of the gene cassettes. (B) The phylogenetic tree of the 14 T. denticola strains, built using the 31 marker genes described in Materials and Methods. Roman numerals in (A) indicate the groups that share significantly more genes as compared to other strains: red numerals indicate that the groupings are consistent with the phylogenetic relationship in (B), and the blue numeral (i.e., group II) highlights an unusual sharing of gene cassettes between not-so-closely-related strains OTK and SP37.