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Updated: Sep 9, 2025

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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.

Biorxiv : the Preprint Server for Biology
|September 2, 2025
PubMed

Insights

Rickettsia bellii uses Sca2/6 for actin-based motility, distinct from other species. This bacterial motility mechanism shows evolutionary flexibility, suggesting adaptability in other microbes.

Area of Science:

  • Microbiology
  • Cell Biology
  • Molecular Biology

Background:

  • Many Rickettsia species utilize actin-based motility for intracellular spread.
  • Rickettsial motility is mediated by effectors like RickA and Sca2.
  • The roles of RickA and Sca2 in Rickettsia bellii remained uncharacterized.

Purpose of the Study:

  • To investigate the function and mechanism of the Sca2 ortholog (Sca2/6) in Rickettsia bellii motility.
  • To compare the motility mechanisms of R. bellii with other Rickettsia species.

Main Methods:

  • Biochemical assays to analyze actin nucleation and elongation by Sca2/6.
  • Microscopy to observe R. bellii motility and actin tail formation in host cells.
  • Comparative analysis of Sca2 orthologs from different Rickettsia species.

Main Results:

  • R. bellii Sca2/6 nucleates and elongates actin via a unique mechanism, distinct from formins.
  • R. bellii motility is a late-infection event solely dependent on Sca2/6.
  • R. bellii exhibits slower, meandering motility with distinct actin tails compared to R. parkeri.

Conclusions:

  • Rickettsia bellii employs a novel actin-based motility mechanism mediated by Sca2/6.
  • The distinct mechanisms highlight the evolutionary adaptability of bacterial motility systems.
  • Understanding these mechanisms provides insights into microbial pathogenesis and host-pathogen interactions.

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