Identification and characterization of a type III secretion system in Chlamydophila psittaciDelphine Sylvie Anne Beeckman1, TomGeens1, Jean-Pierre Timmermans2, Patrick Van Oostveldt1 and Daisy C.G. Vanrompay1
1 Department of Molecular Biotechnology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
2 Department of Veterinary Medicine, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
(Received 8 August 2007; accepted 27 December 2007; published online 15 February 2008)
Abstract - Chlamydiaceae are obligate intracellular Gram-negative bacteria replicating in vacuoles inside eukaryotic cells. It has been proven that most of them possess a type III secretion system (T3SS) allowing them to transfer effector molecules in the host cell. We examined the existence of a T3SS in Chlamydophila psittaci by studying the expression of three essential structural proteins SctW, SctC, and SctN, and one putative effector protein IncA. Immunofluorescence assays showed SctW and IncA to be associated with the bacteria and the inclusion membrane, while SctC and SctN were only localized to the bacteria itself. Immuno electron microscopy could confirm these results for SctW, IncA, and SctC. Unfortunately, SctN was not investigated with this technique. Additionally, we sequenced 14 full-length T3S genes (scc1, sctW, sctJ, sctL, sctR, sctS, scc2, copD1, sctN, sctQ, sctC, incA, ca037, and cadd) and examined the transcription of 26 Cp. psittaci T3S genes namely cluster 1 (scc1, sctW, sctV, sctU), cluster 2 (sctJ, sctL, sctR, sctS, sctT, scc2, copB1, copD1), cluster 3 (sctD, sctN, ca037, sctQ, pkn5, sctC) and non-clustered genes (incA, incC, scc3, copD2, cap1, tarp, ca530, cadd). The gene expression study indicated the T3S structural protein encoding genes to be transcribed from mid-cycle (12-18 h post infection (p.i.)) on. Genes encoding effector proteins and putative T3S related proteins were expressed early (1.5 h-8 h p.i.) or late (>24 h p.i.) during the developmental cycle. We hereby provided evidence for the existence of a T3SS and possible effectors in avian Cp. psittaci.
Key words: Type III secretion / Chlamydia / Chlamydophila psittaci
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