Characterizing the Function of Cyclic di-AMP on Chlamydial Growth and Differentiation

Project Summary: Characterizing the Function of Cyclic di-AMP on Chlamydial Growth and Differentiation Chlamydia is an obligate intracellular bacterial pathogen that causes a range of serious diseases in humans. In developed countries, Chlamydia trachomatis is the primary cause of bacterial sexually transmitted infections (STI). Indeed, recent reports from the Centers for Disease Control highlight the increasing incidence of STIs, with chlamydia infections consistently outpacing all other bacterial causes. In developing countries, C. trachomatis is not only a significant cause of STI, but it is also responsible for the primary cause of infectious preventable blindness, trachoma. The major concern of chlamydial infections is that they are often asymptomatic and undiagnosed, which can lead to chronic sequelae. These include pelvic inflammatory disease, tubal factor infertility, and reactive arthritis for C. trachomatis. Consequently, chlamydial diseases remain a significant burden on health care systems around the world. In adapting to obligate intracellular growth, Chlamydia has significantly reduced its genome size and eliminated genes from various pathways as it relies on the host cell for its metabolic needs. This suggests that the presence of any particular gene(s) is critical, if not essential, for its growth and pathogenesis. Importantly, Chlamydia also alternates between different functional and morphological forms during its normal growth, also referred to as its developmental cycle. These observations, combined with its obligate intracellular dependence, makes Chlamydia a difficult organism with which to work. However, recent development of genetic tools to mechanistically study chlamydiae have significantly enhanced our understanding of this pathogen. Related to this proposal is the observation that Chlamydia produces a second messenger compound, cyclic di-AMP (c-di-AMP), that is known to activate host cell immune-signaling pathways. Interestingly, c-di-AMP is typically produced in Gram-positive bacteria and mycobacteria to regulate aspects of their physiology and pathogenesis, yet Chlamydia is a Gram-negative bacterium. We propose to investigate why Chlamydia produces c-di-AMP and how it functions in the physiology of the organism. The first project goal is to characterize using genetic techniques the effects of altering c-di-AMP production on Chlamydia growth and developmental cycle progression. The second project goal is to identify genes that are regulated by c-di-AMP. Results from the proposed studies will advance our understanding of the function of c-di-AMP in chlamydial physiology and identify new targets for development of Chlamydia-specific treatments.