|Abstract: ||The host-pathogen interaction is dictated by the competition for nutrients. Iron is a rare, but critical component for several conserved biochemical reactions, and as such, is at the forefront in the competition between host and pathogen. The obligate intracellular human pathogen, Chlamydia trachomatis, enters an alternative growth mode when iron is depleted within the host. Termed persistence, this growth mode is characterized by the arrest of development until suitable conditions arise within the host cell, and is likely an important evolutionary mechanism for chronic infection that has been linked to multiple sequelae of infection in vivo. Despite the relevance of persistence in human disease, the sensory and response mechanisms that trigger this alternative growth mode are not understood. The research presented in this report demonstrates a new, robust model for the iron-restriction of intracellular-dwelling C. trachomatis. The model was used to elicit uniform populations of persistent Chlamydiae in vitro, which allowed accurate analysis of differential transcription under iron-starvation conditions. From these studies, the gene ytgA, which is predicted to function as part of an ABC-metal transport complex, was elevated upon low-iron availability.
The identification of the trans- and cis-regulatory factors responsible for the modulation of ytgA transcription was attempted. Our research indicates that the ytgC, which exists in an operon with ytgA, encodes a genetic fusion between a
predicted membrane channel forming polypeptide (N-terminus) and a metal-dependent DNA binding polypeptide (C-terminus), which we have termed C-YtgC. C-YtgC recognized the IGR upstream of ytgA in an iron-dependent manner in vitro, providing a molecular mechanism for the regulation of ytgA under iron-limiting conditions. Two regions containing cis-regulatory elements within the IGR of ytgA were identified for this binding. Additional preliminary evidence suggests a mechanism for the liberation of the C-YtgC polypeptide from the membrane channel portion of the protein. In summary, the research presented in this report has gained significant advances in the field of Chlamydia iron-biology. The search for a robust iron-restriction model has implicated that the chlamydial iron source may be cytosolic, rather than endocytic. Furthermore, the characterization of a novel trans-regulatory factor suggests that Chlamydia may employ a sophisticated regulatory network for maintenance of iron-homeostasis. Continued research into the mechanisms of iron acquisition is warranted, considering the strong link between low-iron availability and chronic infection.|