Capsular Polysaccharide Restrains Type VI Secretion in Acinetobacter baumannii

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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

Nicolas Flaugnatti

Laboratory of Molecular Microbiology, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-6073-3340
Loriane Bader

Laboratory of Molecular Microbiology, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland

Competing interests
The authors declare that no competing interests exist.
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.
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.

"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

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.