Maximum likelihood phylogenetic tree using the HIVw+F+R4 amino acid substitution model. Node support was estimated with 1,000 ultrafast bootstrap replicates and 5,000 replicates for the SH-aLRT test. These variants are from indicated strains of B. burgdorferi (Bb), B. afzelii (Ba), B. garinii (Bg), B. bavariensis (Bbav), B. valaisiana (Bv), B. filandensis (Bf), B. bissettii (Bbis), and B. mayonii (Bm) available on GenBank. Colors denote Pfam54-IV variants of B. burgdorferi strain B31 (blue), B. garinii strain ZQ1 (orange), and B. afzelii strain MMS (green); the red contour line indicates the variants of Pfam54-IV with mouse and/or quail factor H-binding activity, CspA.