Remarkable sequence relatedness in the DNA encoding the major outer membrane protein of Chlamydia psittaci (koala type I) and Chlamydia pneumoniae
Adeeb A. Girjesa, Frank N. Carrickb and Martin F. Lavina
a Queensland Cancer Fund Research Unit, Queensland Institute of Medical Research, Bancroft Centre, Brisbane 4029, Australia; and b Zoology Department, University of Queensland, St. Lucia, Brisbane 4072, Australia.
DNA encoding the major outer membrane protein (MOMP) of the koala type-I strain of Chlamydia psittaci (pathogen responsible for blindness and infertility in koalas) was cloned and sequenced. Comparison with momp gene sequences from other chlamydial species revealed a remarkable degree of homology ( > 97%) with that of the human pathogen, Chlamydia pneumoniae. In comparison, the sequence only shared 75% DNA sequence homology with other C. psittaci members and 69% homology with C. trachomatis. The open reading frame consisted of 1167 bp encoding a 389-amino acid (aa) pre-MOMP including a leader sequence of 23 aa, similar to the C. pneumoniae gene. These genes were closely related even within the four variable domains (86—100% homology). Specific antibodies were capable of distinguishing between koala type I and C. pneumoniae. This very high degree of relatedness between C. pneumoniae, a human pathogen, and an individual strain of C. psittaci in the momp gene raises further questions on the host specificity, classification and evolutionary relationships of the different chlamydial species.