Complete deletion of the <i>Chlamydia muridarum</i> putative cytotoxin locus reveals contributions during invasion in tissue culture and oviduct pathology during murine genital tract infection

Chlamydiaceae is a family of obligate intracellular bacteria that infect a wide range of human and animal hosts. <i>Chlamydia muridarum</i> is a murine-specific species that has been leveraged as an efficacious model of disease mediated by human-specific <i>Chlamydia trachomatis</i>. Genes within the plasticity zone, a region of the chromosome with increased genetic variation across species and serovars, are speculated to contribute to species-specific pathogenesis. <i>C. muridarum</i> expresses three homologous proteins (TC0437-0439) that show similarity to large clostridial cytotoxins. The putative chlamydial cytotoxins have been proposed to mediate immediate toxicity in highly infected epithelial cells by interfering with actin polymerization. We utilized FRAEM mutagenesis to delete all three putative cytotoxins (<i>tc0437-0439</i>). The null strain retained immediate cytotoxicity but exhibited decreased invasion efficiency in tissue culture. During murine infections of the female genital tract, the absence of the putative cytotoxins caused decreased oviduct pathology and did not impact bacterial burden in the upper genital tract. These results indicate that the putative cytotoxins contribute to infection at the cellular level and in the female genital tract of mice.