Phylogeny of Rickettsia spp. inferred by comparing sequences of 'gene D', which encodes an intracytoplasmic protein

'Gene D' is the PS120-protein-encoding gene, first described in Rickettsia conorii and Rickettsia japonica. Sequence analysis of a 3030 bp fragment of 'gene D' in 24 representatives of the genus Rickettsia was carried out to complete phylogenetic analyses previously inferred by comparison of gene se quences encoding citrate synthase, 17 kDa antigen and rOmpA and rOmpB. The phylogenetic relationships between rickettsiae were inferred from the compa rison of both the gene and the derived protein sequences, using the parsimo ny, neighbour-joining and maximum-likelihood methods. Five distinct groups of rickettsiae were identified. These were: the Rickettsia massiliae group, including R, massiliae, Bar 29, Rickettsia rhipicephali and Rickettsia aes chlimannii; the Rickettsia rickettsii group containing Rickettsia sibirica, Rickettsia mongolotimonae', Rickettsia parkeri, strain S, Rickettsia afric ae, the R. conorii complex, Rickettsia slovaca, Rickettsia honei, R. ricket tsii. R. japonica and Rickettsia montanensis; the group currently containin g only Rickettsia helvetica; the Rickettsia akari group including Rickettsi a australis, R. akari and the ELB agent; Rickettsia prowarekii and Ricketts ia typhi clustered in the typhus group. As significant bootstrap values wer e obtained for most of the nodes, sequence comparison of 'gene D' should be considered as a complementary approach in phylogenetic studies of ricketts iae.