(P9) Lateral gene transfer-mediated recombination in Chlamydia trachomatis leads to transitional genomic stages that facilitate tropism to different female and male anatomic sites

Background: C. trachomatis (CT) strains have historically been classified into distinct biovars based on different sites of infection and clinical manifestation. Recent genetic analysis of CT clinical isolates from cervical, ocular, or rectal sites of infection has identified regions of lateral gene transfer-mediated homologous recombination (LGTR) between strains. We reported areas of LGTR in the pmpEFGH gene cluster that shared sequence relatedness between rectal and ocular strains, including an expanded lineage of serovar G and J strains isolated from men who have sex with men (MSM) populations. These data suggest the development of different CT tropism phenotypes through the alteration of the genetic makeup of strains to accommodate environmental and host cell differences found in different anatomic sites.



Methods: Specimens were collected from patients attending Seattle King County Health Department STD Clinics from 1982 through 2010. Standard monoclonal serotyping methods were utilized to initially determine serotypes. Genomic DNA was extracted from specimens and sequenced using Illumina technologies. Resulting read data were assembled and analyzed using the Geneious software suite. A sliding-window-based approach was used to identify regions of LGT in clinical strains.



Results: Through cross-referencing genomic data with the tissue sources of the strains, we identified a distinct rectal lineage separate from known ocular, urogenital, and lymphogranuloma venereum biovars. Isolates of serovars J, D and E collected from the MSM rectum have acquired apparent rectal-tropic genetic signatures through LGTR, which are representative of evolving, transitional genomic stages of tissue tropism. Phylogenetic analysis of transferred regions indicated that ocular strains were the donors in this LGTR and that apparently rectal-specific ompA sequences were moved back into a predecessor cervical-tropic strain. Sliding window analysis of selected transitional J, D, and E rectal strains demonstrated unique and distinct areas of recombination between cervical, ocular, and rectal strains resulting in increasing tropism to the rectal site of infection.



Conclusion: These findings provide further evidence of the involvement of LGTR between urogenital, ocular, and rectal strains in the evolution of CT facilitating variable anatomic site tropism leading toward increased survivability.