Identification of an antigen localized to an apparent septum within dividing chlamydiae

The process of chlamydial cell division has not been thoroughly investigate d. The lack of detectable peptidoglycan and the absence of an FtsZ homolog within chlamydiae suggest an unusual mechanism for the division process. Ou r laboratory has identified an antigen (SEP antigen) localized to a ring-li ke structure at the apparent septum within dividing chlamydial reticulate b odies (RB), Antisera directed against SEP show similar patterns of antigen distribution in Chlamydia trachomatis and Chlamydia psittaci RE. In contras t to Localization in RE, SEP in elementary bodies appears diffuse and irreg ular, suggesting that the distribution of the antigen is developmental-stag e specific, Treatment of chlamydiae with inhibitors of peptidoglycan synthe sis or culture of chlamydiae in medium lacking tryptophan leads to the form ation of nondividing. aberrant RE. Staining of aberrant RE with anti-SEP re veals a marked redistribution of the antigen. Within C. trachomatis-infecte d cells, ampicillin treatment leads to high levels of SEP accumulation at t he periphery of aberrant PP, while in C. psittaci, treatment causes SEP to localize to distinct punctate sites within the bacteria. Aberrancy produced via tryptophan depletion results in a different pattern of SEP distributio n. In either case, the reversal of aberrant formation results in the produc tion of normal RE and a redistribution of SEP to the apparent plane of bact erial division. Collectively these studies identify a unique chlamydial-gen us-common and developmental-stage-specific antigen that may be associated w ith RE division.