Euo is a developmental regulator that represses late genes and activates midcycle genes in Chlamydia trachomatis

The pathogenic bacterium Chlamydia reproduces via an unusual intracellular developmental cycle in which it converts from a dividing form (reticulate body or RB) to an infectious form (elementary body or EB). The transcription factor Euo has been proposed as a developmental regulator in Chlamydia trachomatis because it repressed a number of late chlamydial promoters, which are transcribed during RB-to-EB conversion. To define the Euo regulon, we performed a genome-wide study that combined Euo DNA immunoprecipitation-seq (DIP-seq) studies with RNA-seq analysis of HeLa cells infected with an Euo-overexpressing C. trachomatis strain. We demonstrate that Euo directly regulates ~7% of C. trachomatis genes. However, only about half were downregulated (28/61; 45.9%) by Euo overexpression while paradoxically the other half were upregulated (33/61; 54.1%). Intriguingly, all downregulated genes were late genes, while the majority of upregulated genes were midcycle genes, which are transcribed during RB replication. DIP analysis showed that Euo occupancy sites were restricted to the core promoter region for downregulated genes but were located over a wider region immediately upstream of the promoter for upregulated genes. We also found that Euo controls its own expression through a negative feedback mechanism. Electron microscopy analysis of cells infected with the Euo-overexpressing strain showed fewer EBs, consistent with a block in RB-to-EB conversion, as well as fewer and larger RBs. Together, these findings broaden the role of Euo as a developmental regulator that functions as both a transcriptional repressor of late genes and a transcriptional activator of midcycle genes in C. trachomatis. IMPORTANCE: In this study, we developed a correlative approach that combined DNA immunoprecipitation-seq and RNA-seq analyses to define the regulon of the Chlamydia trachomatis transcription factor Euo. We confirmed the proposed role of Euo as a transcriptional repressor of late chlamydial genes but also showed that Euo activates transcription of a subset of midcycle genes and autoregulates its own expression via negative feedback. This study validates and expands the role of Euo as an important developmental regulator in C. trachomatis. In addition, this genome-wide correlative approach can be applied to study transcription factors in other pathogenic bacteria.