Transformation and Mutagenesis of Chlamydia trachomatis and C. muridarum Utilizing pKW Vector

A gene deletion by allelic exchange via homologous recombination from a bacterial genome represents a valuable genetic tool for studying a role(s) of determinants involved in various aspects of pathogenesis. Due to chlamydial obligate intracellular lifestyle and comparatively low transformation rate, the mutagenesis of Chlamydia utilizes types of suicide vectors that have to be maintained and propagated by the bacteria throughout several rounds of their intracellular developmental cycle. These deletion constructs must be lost by chlamydiae once null mutant formation is achieved. pKW is a small, 5.45 bp, pUC19-derived vector, which has been recently successfully employed for the generation of deletion mutants in C. trachomatis, serovariant D, and C. muridarum. This vector contains both, E. coli as well as chlamydial species-specific plasmid origins of replication, allowing for its propagation by both bacterial genera under a selective pressure. However, once the selective antibiotic is removed from culture, chlamydiae rapidly lose pKW, and the subsequent reintroduction of the selective antibiotic back to chlamydiae-infected cells results efficiently in the selection of generated deletion mutants. Protocols provided here describe in detail the preparation of pKW deletion constructs for C. trachomatis and C. muridarum applicable for chlamydial transformation and the production of null mutant in non-essential genes. Protocols provided here, are describing in detail methods for assembly of the pKW shuttle vector and generation of deletion mutants in C. trachomatis and C. muridarum.