Abstract
The development of genetic transformation technology for Chlamydia trachomatis using its endogenous plasmid has recently been described. Chlamydia muridarum cannot be transformed by the C. trachomatis plasmid, indicating a barrier between chlamydial species. To determine which regions of the plasmid conferred the species specificity, we used the novel approach of transforming wild-type C. muridarum carrying the endogenous plasmid pNigg and forced recombination with the C. trachomatis vector pGFP::SW2 which carries the complete C. trachomatis plasmid (pSW2). Penicillin and chloramphenicol-resistant transformants expressing the green fluorescent protein were selected. Recovery of plasmids from these transformants showed they were recombinants. The differences between the pSW2 and pNigg allowed identification of the recombination breakpoints and showed that pGFP::SW2 had exchanged a ∼ 1 kbp region with pNigg covering CDS 2. The recombinant plasmid (pSW2NiggCDS2) is maintained under antibiotic selection when transformed into plasmid-cured C. muridarum. The ability to select for recombinants in C. muridarum shows that the barrier is not at transformation, but at the level of plasmid replication or maintenance. Our studies show that CDS 2, together with adjoining sequences, is the main determinant of plasmid tropism.
Highlights
There are nine recognised species of Chlamydia each with distinctive biological properties such as a specific tissue tropism and disease pathology
Tropism of the C. trachomatis plasmid is determined by CDS2 et al, 1997; Stothard et al, 1998; Wang et al, 2013a)
For the productive replication of plasmid pGFP::SW2 in C. muridarum, the C. trachomatis progenitor plasmid’s entire coding sequences (CDS) 2, with some short flanking regions was replaced by the orthologous region from the C. muridarum plasmid pNigg
Summary
There are nine recognised species of Chlamydia each with distinctive biological properties such as a specific tissue tropism and disease pathology. Repeated attempts to transform C. muridarum Nigg P- as the recipient host with the C. trachomatis/ Escherichia coli plasmid shuttle vector pGFP::SW2 were unsuccessful in our hands, consistent with previous observations (Song et al, 2014).
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