| Summary: | Indiana University-Purdue University Indianapolis (IUPUI) === Chlamydia trachomatis is an obligate intracellular bacterial pathogen that
can infect the eyes, genital tract, and disseminate to lymph nodes in humans.
Many C. trachomatis infections are clinically asymptomatic and can become
chronic if left untreated. When humans are infected with C. trachomatis, a
cytokine that is produced is interferon-gamma (IFN-γ). In vitro, IFN-γ stimulates
expression of the host enzyme indoleamine 2,3-dioxygenase. This enzyme
converts free intracellular tryptophan to N-formylkynurenine. Tryptophan
starvation induces C. trachomatis to enter a viable-but-nonculturable state
termed persistence, which has been proposed to play a key role in chronic
Chlamydial disease. To circumvent host induced tryptophan depletion,
urogenital strains of C. trachomatis encode a functional tryptophan synthase
(TS). TS synthesizes tryptophan from indole and serine, allowing Chlamydia to
reactivate from persistence. Transcriptomic analysis revealed C. trachomatis
differentially regulates hundreds of genes in response to tryptophan starvation.
However, genes that mediate entry, survival, and reactivation from persistence
remain largely unknown. Using a forward genetic screen, we identified six
Susceptible to IFN-γ mediated Persistence (Sip) mutants that have diminished
capacities to reactivate from persistence with indole. Mapping the deleterious
persistence alleles in three of the Sip mutants revealed that only one of the
mutants had a mutation in TS. The two other Sip mutants mapped had mutations in CTL0225, a putative integral membrane protein, and CTL0694, a
putative oxidoreductase. Neither of these genes plays a known role in
tryptophan synthesis. However, amino acid (AA) competitive inhibition assays
suggest that CTL0225 may be involved in the transport of leucine, isoleucine,
valine, cysteine, alanine, and serine. Additionally, metabolomics analysis
indicates that all free amino acids are depleted in response to IFN-γ, making this
amino acid transporter essential during persistence. Taken together we have
identified two new chlamydial persistence genes that may play a role in chronic
chlamydial disease.
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