Chlamydia muridarum TC0066 is required for invasion and intracellular development in tissue culture but dispensable in the murine infection model

Members of the Family Chlamydiaceae are obligate intracellular bacteria displaying a range of host and tissue tropisms. Genetic tractability, first established for Chlamydia trachomatis LGV serovar L2, is now being expanded to additional Chlamydia species. This capability facilitates the comparative assessment of chlamydial virulence factors during infection. All Chlamydia spp. express a type III secretion system, and the translocated membrane-associated protein A (TmeA) represents a pivotal effector exhibiting species-specific divergence. Chlamydia muridarum is a murine-specific species that has been leveraged in a host-appropriate small-animal model of disease. We utilized FRAEM mutagenesis to delete the putative tmeA ortholog tc0066 in C. muridarum to enable pathogenesis studies. Work confirms that, similar to TmeA, TC0066 is capable of interacting with host AHNAK and N-WASP. The interaction with N-WASP was important for C. muridarum invasion and for subsequent intracellular development in tissue culture. During murine infections of the female genital tract, the absence of tc0066 did not impact infection parameters, including bacterial shedding or gross pathology. These results indicate that TC0066 and C. trachomatis TmeA exhibit conserved functions, but these activities do not translate to detectable, overt changes to in vivo genital-tract pathogenesis.

IMPORTANCE

Chlamydia spp. are prevalent pathogens capable of infecting a wide range of hosts and tissues, yet the molecular determinants mediating differences in tropism remain incompletely defined. Chlamydia trachomatis employs a type III secreted effector protein, TmeA, to manipulate Arp2/3-dependent actin polymerization in order to create and maintain a protected intracellular niche. The tmeA -encoding locus shows evidence of divergence among chlamydial species. We demonstrate herein that C. muridarum TC0066 represents a functionally conserved TmeA homolog and leverage this similarity to probe the contribution of this effector to chlamydial pathogenesis. Results from murine infection studies using mutant C. muridarum strains contrast with those from C. trachomatis , emphasizing the need for care when interpreting outcomes of human chlamydial infection in the murine model.