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Bacterial type III secretion systems are ancient and evolved by multiple horizontal-transfer events.
Uri Gophna1, Eliora Z Ron, Dan Graur
1Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel 69978. urigo@post.tau.ac.il
Gene
|August 12, 2003
Summary
Type III secretion systems (TTSS) and flagellar export mechanisms share a common ancestor but evolved independently. Horizontal gene transfer significantly shaped TTSS evolution, occurring earlier and more frequently than previously thought.
Area of Science:
- Microbiology
- Evolutionary Biology
- Bacterial Pathogenesis
Background:
- Type III secretion systems (TTSS) are crucial bacterial virulence factors mediating host-pathogen interactions.
- Structural similarities between TTSS proteins and flagellar export proteins suggest a shared evolutionary origin.
Purpose of the Study:
- To reconstruct the evolutionary history of conserved TTSS proteins and their flagellar paralogs.
- To investigate the evolutionary relationship between TTSS and flagellar export systems.
- To identify the role of horizontal gene transfer in TTSS evolution.
Main Methods:
- Phylogenetic analysis of four conserved TTSS proteins.
- Comparison of protein phylogenies with the 16S rDNA species tree.
- Identification of lateral gene transfer events.
Main Results:
- TTSS and flagellar export mechanisms share a common ancestor but have distinct evolutionary trajectories.
- The hypothesis of TTSS gene evolution directly from flagellar genes is refuted.
- Multiple, early, and frequent horizontal gene transfer events involving TTSS gene clusters were identified.
Conclusions:
- TTSS and flagellar systems are independently evolved from a common ancestral export machinery.
- Horizontal gene transfer is a major driver in the evolution of TTSS and the species that utilize them.
- Previous estimates of horizontal gene transfer frequency in TTSS evolution are likely underestimated.