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Updated: Apr 30, 2026
An Electroporation Method to Transform Rickettsia spp. with a Fluorescent Protein-Expressing Shuttle Vector in Tick Cell Lines
Published on: October 11, 2022
Divergent Rickettsia species exhibit distinct mechanisms of actin-based motility
Meghan C Bacher1, Julie E Choe1, Jiawen Jiang2
1Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, USA.
Abstract:
Many Rickettsia species undergo actin-based motility to promote cell-cell spread during infection. Rickettsial genomes often encode two motility effectors, RickA and Sca2, which in the spotted fever group I species, Rickettsia parkeri act by activating the host Arp2/3 complex and by mimicking eukaryotic formins, respectively. The function of RickA and Sca2 orthologs in the distantly related species Rickettsia bellii was unclear. We report that R. bellii RickA activates the host Arp2/3 complex but has no discernible role in bacterial motility. The R. bellii Sca2 ortholog, Sca2/6, nucleates and elongates actin with a flexible structure and an unusual actin monomer-binding motif in a mechanism distinct from formins or other microbial actin nucleators. R. bellii motility is solely correlated with Sca2/6 localization and, compared with R. parkeri motility, is slow and meandering, generating distinctly organized actin tails. The evolutionary flexibility in the mechanism and regulation of rickettsial actin-based motility suggests similar adaptability for other microbes.
Insights
Rickettsia bellii uses a unique Sca2/6 protein for actin-based motility, distinct from other Rickettsia species. This finding reveals evolutionary flexibility in microbial actin motility mechanisms.
Area of Science:
- Microbiology
- Cell Biology
- Molecular Biology
Background:
- Actin-based motility is crucial for cell-cell spread in many Rickettsia species.
- Rickettsia species typically encode RickA and Sca2 proteins for motility, with distinct roles in Rickettsia parkeri.
Purpose of the Study:
- To investigate the roles of RickA and Sca2 orthologs in the motility of Rickettsia bellii.
- To elucidate the mechanism of actin nucleation and elongation by R. bellii Sca2/6.
Main Methods:
- Investigated R. bellii RickA's interaction with the host Arp2/3 complex.
- Characterized the actin-binding and nucleating properties of R. bellii Sca2/6.
- Observed and compared the motility patterns and actin tail structures of R. bellii and R. parkeri.
Main Results:
- R. bellii RickA activates the host Arp2/3 complex but does not contribute to bacterial motility.
- R. bellii Sca2/6 functions as a novel actin nucleator and elongator, distinct from formins.
- R. bellii exhibits slow, meandering motility solely dependent on Sca2/6, with unique actin tail organization.
Conclusions:
- R. bellii employs a unique mechanism for actin-based motility driven by Sca2/6.
- The study highlights the evolutionary adaptability of actin-based motility mechanisms in Rickettsia.
- Findings suggest potential for similar adaptability in other microbial systems.
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