Genome Copy Number Regulates Inclusion Expansion, Septation, and Infectious Developmental Form Conversion in Chlamydia trachomatis

ABSTRACT

DNA replication is essential for the growth and development of Chlamydia trachomatis; however, it is unclear how this process contributes to and is controlled by the pathogen’s biphasic life cycle. While inhibitors of transcription, translation, cell division, and glucose-6-phosphate transport all negatively affect chlamydial intracellular development, the effects of directly inhibiting DNA polymerase have never been examined. We isolated a temperature-sensitive dnaE mutant (the dnaE^ts mutant) that exhibits an ∼100-fold reduction in genome copy number at the nonpermissive temperature (40°C) but replicates similarly to the parent at the permissive temperature of 37°C. We measured higher ratios of genomic DNA nearer the origin of replication than the terminus in the dnaE^ts mutant at 40°C, indicating that this replication deficiency is due to a defect in DNA polymerase processivity. The dnaE^ts mutant formed fewer and smaller pathogenic vacuoles (inclusions) at 40°C, and the bacteria appeared enlarged and exhibited defects in cell division. The bacteria also lacked both discernible peptidoglycan and polymerized MreB, the major cell division-organizing protein in Chlamydia responsible for nascent peptidoglycan biosynthesis. We also found that the absolute genome copy number, rather than active genome replication, was sufficient for infectious progeny production. Deficiencies in both genome replication and inclusion expansion were reversed when the dnaE^ts mutant was shifted from 40°C to 37°C early in infection, and intragenic suppressor mutations in dnaE^ts also restored genome replication and inclusion expansion in the dnaE^ts mutant at 40°C. Overall, our results show that genome replication in C. trachomatis is required for inclusion expansion, septum formation, and the transition between the microbe’s replicative and infectious forms.

IMPORTANCE Chlamydiae transition between infectious, extracellular elementary bodies (EBs) and noninfectious, intracellular reticulate bodies (RBs). Some checkpoints that govern transitions in chlamydial development have been identified, but the extent to which genome replication plays a role in regulating the pathogen’s infectious cycle has not been characterized. We show that genome replication is dispensable for EB-to-RB conversion but is necessary for RB proliferation, division septum formation, and inclusion expansion. We use new methods to investigate developmental checkpoints and dependencies in Chlamydia that facilitate the ordering of events in the microbe’s biphasic life cycle. Our findings suggest that Chlamydia utilizes feedback inhibition to regulate core metabolic processes during development, likely an adaptation to intracellular stress and a nutrient-limiting environment.