| Chlamydia is an obligate, intracellular bacterial pathogen that causes a wide range of diseases in both humans and animals. Chlamydia undergoes a developmental cycle that alternates between an infectious, metabolically inert form, the elementary body (EB), and a non-infectious, metabolically active form, the reticulate body (RB). Additionally, Chlamydia can readily enter a nonproductive growth state, termed persistence, which confers some resistance towards varied stresses. Persistent chlamydiae are viable but do not divide and have aberrant morphology. Because of this life cycle and obligate dependence on a host cell, no stable transformation system has been developed. The inability to target genes for disruption and to subsequently select these mutants renders this organism refractory to typical molecular experimental approaches. However, recent advances in gene expression assays, including quantitative RT-PCR and microarray, coupled with the sequencing of several chlamydial genomes, have facilitated studies of chlamydial microbiology. Data presented in this study have furthered our understanding of both developmental gene expression and regulation and gene expression changes that occur during persistence. An analysis of two developmentally-regulated paralogous operons showed that they have similar promoter structures, implicating the same sigma factor in controlling their expression. Using novel methodological and analytical approaches, I have shown that genomic normalization is the preferred method of analyzing gene expression data. This approach has led to the novel finding that, during IFNgamma-mediated persistence, chlamydial gene expression becomes dysregulated as evidenced by a global increase in transcription across the chromosome. The normal mechanisms used to control developmental gene expression do not appear to operate during this persistent state, and this effect is likely due to inefficient translation. Collectively, data presented here have significantly altered the ways in which researchers consider chlamydial developmental gene regulation during both productive and non-productive growth states. |
