PHYLOGENETIC ANALYSES OF CHLAMYDIA-PSITTACI STRAINS FROM BIRDS BASED ON 16S RIBOSOMAL-RNA GENE SEQUENCE

The nucleotide sequences of 165 ribosomal DNA (rDNA) were determined f or 39 strains of Chlamydia psittaci (34 from birds and 5 from mammals) and for 4 Chlamydia pecorum strains, The sequences were compared phyl ogenetically with the gene sequences of nine Chlamydia strains (coveri ng four species of the genus) retrieved from nucleotide databases. In the neighbor-joining tree, C. psittaci strains were more closely relat ed to each other than to the other Chlamidia species, although a felin e pneumonitis strain was distinct (98.3 to 98.6% similarity to other s trains) and appeared to form the deepest subline within the species of C psittaci (bootstrap value, 99%), The other strains of C, psittaci e xhibiting similarity values of more than 99% were branched into severa l subgroups, Tyro pigeon strains and one turkey strain formed a distin ct clade recovered in 97% of the bootstrapped trees. The other pigeon strains seemed to be distinct from the strains from psittacine birds, with 88% of bootstrap value. In the cluster of psittacine strains, thr ee parakeet strains and an ovine abortion strain exhibited a specific association (level of sequence similarity, 99.9% or more; bootstrap va lue, 95%). These suggest that at least four groups of strains exist wi thin the species C, psittaci. The 16S rDNA sequence is a valuable phyl ogenetic marker for the taxonomy of chlamydiae, and its analysis is a reliable tool for identification of the organisms.