Beyond Tryptophan Synthase: Identification of Genes That Contribute to Chlamydia trachomatis Survival during Gamma Interferon-Induced Persistence and Reactivation
Chlamydia trachomatiscan enter a viable but nonculturable statein vitrotermed persistence. A common feature ofC. trachomatispersistence models is that reticulate bodies fail to divide and make few infectious progeny until the persistence-inducing stressor is removed. One model of persistence that has relevance to human disease involves tryptophan limitation mediated by the host enzyme indoleamine 2,3-dioxygenase, which convertsl-tryptophan toN-formylkynurenine. GenitalC. trachomatisstrains can counter tryptophan limitation because they encode a tryptophan-synthesizing enzyme. Tryptophan synthase is the only enzyme that has been confirmed to play a role in interferon gamma (IFN-γ)-induced persistence, although profound changes in chlamydial physiology and gene expression occur in the presence of persistence-inducing stressors. Thus, we screened a population of mutagenizedC. trachomatisstrains for mutants that failed to reactivate from IFN-γ-induced persistence. Six mutants were identified, and the mutations linked to the persistence phenotype in three of these were successfully mapped. One mutant had a missense mutation in tryptophan synthase; however, this mutant behaved differently from previously described synthase null mutants. Two hypothetical genes of unknown function,ctl0225andctl0694, were also identified and may be involved in amino acid transport and DNA damage repair, respectively. Our results indicate thatC. trachomatisutilizes functionally diverse genes to mediate survival during and reactivation from persistence in HeLa cells.