The tree was generated using neighbor-joining distance method and 1000 bootstrap replicates. Bootstrap values >50% are shown at the nodes. Bar, nucleotide distance. ‘R. monacensis’ str. Humboldt (or Rickettsia endosymbiont Ixodes pacificus) is represented at the top of the tree. Other selected sequences on the tree include: R. aeschlimannii, R. africae, R. akari, R. australis, R. buchneri, R. conorii, R. felis, R. heilongjiangensis, R. honei, R. japonica, R. massiliae, ‘R. monacensis’ str. IrR/Munich, R. montanensis, R. parkeri, R. peacockii, R. philipii, R. raoultii, R. rhipicephali, R. rickettsii, R. sibirica, and R. slovaca. The accession numbers of genes of all Rickettsia species are listed in Supplemental Table.