CENTRAL CARBON METABOLISM AND OBGE-MEDIATED CONTROL OF CHLAMYDIA TRACHOMATIS DEVELOPMENTAL TRANSITIONS

Colleen Ceja Monahan

Chlamydia trachomatis is an obligate intracellular bacterial pathogen that causes significant disease in humans. Within the species, serovars A-C are associated with blinding ocular infections while serovars D-L are associated with sexually transmitted infections. Blinding ocular infections, known as trachoma, are a public health concern in over 40 countries and are responsible for permanently blinding two million individuals. C. trachomatis is the most common sexually transmitted pathogen worldwide with over 100 million new cases reported annually. In addition to causing infertility, C. trachomatis sexually transmitted infections are associated with increased risk of cervical cancer and HIV transmission. Chlamydial pathogenesis is dependent on the infection of a host cell and the transition between the infectious, non-replicative Elementary Body (EB) and the non-infectious Reticulate Body (RB) inside a vacuole known as the chlamydial inclusion. While it is recognized that the EB and RB possess distinct gene expression patterns and metabolic profiles, the mechanisms that regulate the Chlamydia developmental cycle are unresolved. Central carbon metabolism and a nutrient-sensitive GTPase, ObgE, have been documented to influence bacterial growth and morphological transitions in other prokaryotes; however, their role in regulating the chlamydial developmental cycle is ambiguous. First, to investigate the role of central carbon metabolism during C. trachomatis developmental transitions we ectopically overexpressed glucose-6-phosphate dehydrogenase (G6PD) and pyruvate kinase (Pyk). G6PD and Pyk catalyze rate-limiting enzymatic reactions in the pentose phosphate pathway and glycolysis, respectively. Therefore, they are significant metabolic nodes in central carbon metabolism. Ectopic overexpression of G6PD and Pyk had distinct effects on chlamydial replication, morphological transitions, and transcription of genes associated with central carbon metabolism and specific cell forms. These data strongly suggest that G6PD and Pyk in part regulate developmental cycle kinetics in Chlamydia. Second, the role of ObgE in regulating the chlamydial developmental cycle was determined through ectopic overexpression and knockdown of ObgE/obgE expression in C. trachomatis. ObgE is a highly conversed GTPase predicted to be important during the C. trachomatis developmental cycle due to its conserved function in other bacteria, as well as being expressed during timepoints corresponding to logarithmic growth and critical developmental transitions in Chlamydia. Ectopic overexpression of ObgE negatively affected EB formation without altering bacterial morphology and downregulated expression of EB-specific genes. In contrast, knockdown of obgE severely affected RB replication, bacterial ultrastructure, EB formation, and expression of RB-associated genes. Together, these data demonstrate that balanced expression of ObgE is necessary for proper progression through the developmental cycle. In conclusion, the regulation of the Chlamydia developmental cycle is dependent on proper expression of G6PD, Pyk, and ObgE.

CENTRAL CARBON METABOLISM AND OBGE-MEDIATED CONTROL OF CHLAMYDIA TRACHOMATIS DEVELOPMENTAL TRANSITIONS

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