1. Microbiology and Infectious Disease

Capsular Polysaccharide Restrains Type VI Secretion in Acinetobacter baumannii

  1. Nicolas Flaugnatti
  2. Loriane Bader
  3. Mary Croisier-Coeytaux
  4. Melanie Blokesch  Is a corresponding author
  1. Ecole Polytechnique Federale de Lausanne, Switzerland
  2. Swiss Federal Institute of Technology Lausanne, Switzerland
https://doi.org/10.7554/eLife.101032
Share this article
Cite this article
  1. Nicolas Flaugnatti
  2. Loriane Bader
  3. Mary Croisier-Coeytaux
  4. Melanie Blokesch
(2025)
Capsular Polysaccharide Restrains Type VI Secretion in Acinetobacter baumannii
eLife 14:e101032.
https://doi.org/10.7554/eLife.101032
  2. Download BibTeX
  3. Download .RIS

Abstract

The type VI secretion system (T6SS) is a sophisticated, contact-dependent nanomachine involved in interbacterial competition. To function effectively, the T6SS must penetrate the membranes of both attacker and target bacteria. Structures associated with the cell envelope, like polysaccharides chains, can therefore introduce spatial separation and steric hindrance, potentially affecting the efficacy of the T6SS. In this study, we examined how the capsular polysaccharide (CPS) of Acinetobacter baumannii affects T6SS's antibacterial function. Our findings show that the CPS confers resistance against T6SS-mediated assaults from rival bacteria. Notably, under typical growth conditions, the presence of the surface-bound capsule also reduces the efficacy of the bacterium's own T6SS. This T6SS impairment is further enhanced when CPS is overproduced due to genetic modifications or antibiotic treatment. Furthermore, we demonstrate that the bacterium adjusts the level of the T6SS inner tube protein Hcp according to its secretion capacity, by initiating a degradation process involving the ClpXP protease. Collectively, our findings contribute to a better understanding of the dynamic relationship between T6SS and CPS and how they respond swiftly to environmental challenges.

Data availability

Imaging dataset: All scripts, models, and classifiers used for image analyses have been deposited on Zenodo (https://doi.org/10.5281/zenodo.11039744).All raw images used in this study have been deposited on Zenodo (https://doi.org/10.5281/zenodo.14386836).All other data are included in the manuscript, with source data provided in Supplementary File 3.

Article and author information

Author details

  1. Nicolas Flaugnatti

    Laboratory of Molecular Microbiology, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-6073-3340

  2. Loriane Bader

    Laboratory of Molecular Microbiology, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
    Competing interests
    The authors declare that no competing interests exist.

  3. Mary Croisier-Coeytaux

    Bioelectron Microscopy Core Facility, Swiss Federal Institute of Technology Lausanne, Lausanne, Switzerland
    Competing interests
    The authors declare that no competing interests exist.

  4. Melanie Blokesch

    Laboratory of Molecular Microbiology, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
    For correspondence
    melanie.blokesch@epfl.ch
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-7024-1489

Funding

Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (407240_167061)

  • Melanie Blokesch

Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (310030_204335)

  • Melanie Blokesch

Howard Hughes Medical Institute (55008726)

  • Melanie Blokesch

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Copyright

© 2025, Flaugnatti et al.

This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 451
    views
  • 110
    downloads
  • 0
    citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Nicolas Flaugnatti
  2. Loriane Bader
  3. Mary Croisier-Coeytaux
  4. Melanie Blokesch
(2025)
Capsular Polysaccharide Restrains Type VI Secretion in Acinetobacter baumannii
eLife 14:e101032.
https://doi.org/10.7554/eLife.101032

Share this article

https://doi.org/10.7554/eLife.101032

Categories and tags

Further reading

    1. Microbiology and Infectious Disease

    Amidase and lysozyme dual functions in TseP reveal a new family of chimeric effectors in the type VI secretion system

    Zeng-Hang Wang, Ying An ... Tao Dong
    Research Article

    Peptidoglycan (PG) serves as an essential target for antimicrobial development. An overlooked reservoir of antimicrobials lies in the form of PG-hydrolyzing enzymes naturally produced for polymicrobial competition, particularly those associated with the type VI secretion system (T6SS). Here, we report that a T6SS effector TseP, from Aeromonas dhakensis, represents a family of effectors with dual amidase-lysozyme activities. In vitro PG-digestion coupled with LC-MS analysis revealed the N-domain’s amidase activity, which is neutralized by either catalytic mutations or the presence of the immunity protein TsiP. The N-domain, but not the C-domain, of TseP is sufficient to restore T6SS secretion in T6SS-defective mutants, underscoring its critical structural role. Using pull-down and secretion assays, we showed that these two domains interact directly with a carrier protein VgrG2 and can be secreted separately. Homologs in Aeromonas hydrophila and Pseudomonas syringae exhibited analogous dual functions. Additionally, N- and C-domains display distinctive GC contents, suggesting an evolutionary fusion event. By altering the surface charge through structural-guided design, we engineered the TsePC4+ effector that successfully lyses otherwise resistant Bacillus subtilis cells, enabling the T6SS to inhibit B. subtilis in a contact-independent manner. This research uncovers TseP as a new family of bifunctional chimeric effectors targeting PG, offering a potential strategy to harness these proteins in the fight against antimicrobial resistance.

    1. Biochemistry and Chemical Biology
    2. Microbiology and Infectious Disease

    On the role of VP3-PI3P interaction in birnavirus endosomal membrane targeting

    Flavia A Zanetti, Ignacio Fernandez ... Laura Ruth Delgui
    Research Article

    Birnaviruses are a group of double-stranded RNA (dsRNA) viruses infecting birds, fish, and insects. Early endosomes (EE) constitute the platform for viral replication. Here, we study the mechanism of birnaviral targeting of EE membranes. Using the Infectious Bursal Disease Virus (IBDV) as a model, we validate that the viral protein 3 (VP3) binds to phosphatidylinositol-3-phosphate (PI3P) present in EE membranes. We identify the domain of VP3 involved in PI3P-binding, named P2 and localized in the core of VP3, and establish the critical role of the arginine at position 200 (R200), conserved among all known birnaviruses. Mutating R200 abolishes viral replication. Moreover, we propose a two-stage modular mechanism for VP3 association with EE. Firstly, the carboxy-terminal region of VP3 adsorbs on the membrane, and then the VP3 core reinforces the membrane engagement by specifically binding PI3P through its P2 domain, additionally promoting PI3P accumulation.

    1. Biochemistry and Chemical Biology
    2. Microbiology and Infectious Disease

    Cellular Energy Production: Mycofactocin and the mycobacterial electron transport chain

    Stephanie M Stuteley, Ghader Bashiri
    Insight

    In the bacterium M. smegmatis, an enzyme called MftG allows the cofactor mycofactocin to transfer electrons released during ethanol metabolism to the electron transport chain.