Chlamydia trachomatis Plasmid-Encoded Pgp4 Is a Transcriptional Regulator of Virulence-Associated Genes

ABSTRACTChlamydia trachomatiscauses chronic inflammatory diseases of the eye and genital tract and has global medical importance. The chlamydial plasmid plays an important role in the pathophysiology of these diseases, as plasmid-deficient organisms are highly attenuated. The cryptic plasmid carries noncoding RNAs and eight conserved open reading frames (ORFs). To understand plasmid gene function, we generated plasmid shuttle vectors with deletions in each of the eight ORFs. The individual deletion mutants were used to transform chlamydiae and the transformants were characterized phenotypically and at the transcriptional level. We show thatpgp1, -2, -6, and -8are essential for plasmid maintenance, while the other ORFs can be deleted and the plasmid stably maintained. We further show that apgp4knockout mutant exhibits anin vitrophenotype similar to its isogenic plasmidless strain, in terms of abnormal inclusion morphology and lack of glycogen accumulation. Microarray and qRT-PCR analysis revealed that Pgp4 is a transcriptional regulator of plasmid-encodedpgp3and multiple chromosomal genes, including the glycogen synthase geneglgA, that are likely important in chlamydial virulence. Our findings have major implications for understanding the plasmid's role in chlamydial pathogenesis at the molecular level.