Dendrogram representing phylogenetic relationships between Rickettsia species inferred from comparison of Sca1 amino acid sequences. The Neighbor-Joining phylogenetic tree was inferred with the MEGA software version 2.1. The numbers at the nodes are the proportion of 100 bootstrap resamplings that support the topology shown. The scale bar indicates a 5 % sequence divergence. 1A: phylogeny of all 20 species using an alignment of the autotransporter domain; 1B: phylogeny of spotted fever group rickettsiae inferred from the comparison of full Sca1 sequences; 1C: phylogenetic resolution of members of the R. rickettsii and R. massiliae clusters.