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Applying Live Cell Imaging and Cryo-Electron Tomography to Resolve Spatiotemporal Features of the Legionella pneumophila Dot/Icm Secretion System
Published on: March 10, 2020
A Novel Pilus System in Candidate Phyla Radiation Bacteria
Biorxiv : the Preprint Server for Biology
|June 22, 2026
Summary
Researchers identified novel pilins, PamA and PamB, that form unique filaments in Candidate Phyla Radiation (CPR) bacteria. This discovery reveals new bacterial assembly mechanisms and expands our understanding of CPR diversity.
Area of Science:
- Microbiology
- Structural Biology
- Bacterial Pathogenesis
Background:
- Candidate Phyla Radiation (CPR) bacteria constitute a significant portion of microbial life but are difficult to study.
- Extracellular filaments of the parasitic CPR bacterium *Candidatus* Mycosynbacter amalyticus are crucial for host interaction but their composition was unknown.
Purpose of the Study:
- To determine the molecular identity and structure of the extracellular filaments produced by *Candidatus* Mycosynbacter amalyticus.
- To elucidate the assembly mechanism and evolutionary origin of these novel filaments.
Main Methods:
- Single-particle cryo-electron microscopy was used to obtain high-resolution structures of the filaments.
- Bioinformatic and phylogenetic analyses were performed to identify homologous proteins and conserved genes.
Main Results:
- Two novel pilins, PamA and PamB, were identified and structurally characterized, revealing unique helical filament assembly.
- Pam pilins share conserved structural features like Ig-like folds and donor-strand exchange, despite low sequence identity.
- Pam pilins are exclusive to CPR bacteria, with homologs found in Saccharimonadia and Microgenomatia classes.
Conclusions:
- The study reveals a novel bacterial pilus system with a distinct assembly pathway, expanding the known diversity of extracellular structures.
- Structural determination of PamA and PamB highlights the utility of advanced imaging techniques for characterizing uncultured CPR bacteria.
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