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Journal of Bacteriology, December 2009, p. 7182-7192, Vol. 191, No. 23
0021-9193/09/$08.00+0     doi:10.1128/JB.00895-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Evolutionary Dynamics of ompA, the Gene Encoding the Chlamydia trachomatis Key Antigen {triangledown} ,{dagger}

Alexandra Nunes,1 Maria J. Borrego,1 Baltazar Nunes,2 Carlos Florindo,1 and João P. Gomes1*

Department of Infectious Diseases, National Institute of Health, Av. Padre Cruz, Lisbon, Portugal,1 Department of Epidemiology, National Institute of Health, Av. Padre Cruz, Lisbon, Portugal2

Received 9 July 2009/ Accepted 18 September 2009

Chlamydia trachomatis is the trachoma agent and causes most bacterial sexually transmitted infections worldwide. Its major outer membrane protein (MOMP) is a well-known porin and adhesin and is the dominant antigen. So far, investigation of MOMP variability has been focused mainly on molecular epidemiological surveys. In contrast, we aimed to evaluate the impact of the host pressure on this key antigen by analyzing its evolutionary dynamics in 795 isolates from urogenital infections, taking into account the MOMP secondary structure and the sizes/positions of antigenic regions. One-third of the specimens showed a mutational drift from the corresponding genotype, where ~42% of the mutations had never been described. Amino acid alterations were sixfold more frequent within B-cell epitopes than in the remaining protein (P = 0.027), and some mutations were also found within or close to T-cell antigenic clusters. Interestingly, the two most ecologically successful genotypes, E and F, showed a mutation rate 60.3-fold lower than that of the other genotypes (P < 10–8), suggesting that their efficacy may be the result of a better fitness in dealing with the host immune system rather than of specific virulence factors. Furthermore, the variability exhibited by some genetic variants involved residues that are known to play a critical role during the membrane mechanical movements, contributing to a more stable and flexible porin conformation, which suggests some plasticity to deal with environmental pressure. Globally, these MOMP mutational trends yielded no mosaic structures or important phylogenetic changes, but instead yielded point mutations on specific protein domains, which may enhance pathogen's infectivity, persistence, and transmission.

* Corresponding author. Mailing address: Department of Infectious Diseases, National Institute of Health, Av. Padre Cruz, 1649-016 Lisbon, Portugal. Phone: (315) 217 519 241. Fax: (351) 217 526 400. E-mail: j.paulo.gomes{at}insa.min-saude.pt

{triangledown} Published ahead of print on 25 September 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, December 2009, p. 7182-7192, Vol. 191, No. 23
0021-9193/09/$08.00+0     doi:10.1128/JB.00895-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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