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A membrane-depolarizing toxin substrate of the Staphylococcus aureus Type VII secretion system mediates intra-species competition

Lookup NU author(s): Dr Fatima Ulhuq, Dr Chriselle Mendonca, Dr Grant Buchanan, Dr Henrik Strahl von SchultenORCiD, Professor Matthias TrostORCiD, Professor Tracy Palmer FRS FRSE FMedSciORCiD



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


The type VII protein secretion system (T7SS) is conserved across Staphylococcus aureus strains and plays important roles in virulence and interbacterial competition. To date only one T7SS substrate protein, encoded in a subset of S. aureus genomes, has been functionally characterized. Here, using an unbiased proteomic approach, we identify TspA as a further T7SS substrate. TspA is encoded distantly from the T7SS gene cluster and is found across all S. aureus strains as well as in Listeria and Enterococci. Heterologous expression of TspA from S. aureus strain RN6390 indicates its C-terminal domain is toxic when targeted to the Escherichia coli periplasm and that it depolarizes the cytoplasmic membrane. The membrane depolarizing activity is alleviated by co-production of the membrane-bound TsaI immunity protein, which is encoded adjacent to tspA on the S. aureus chromosome. Using a zebrafish hindbrain ventricle infection model, we demonstrate that the T7SS of strain RN6390 promotes bacterial replication in vivo, and deletion of tspA leads to increased bacterial clearance. The toxin domain of TspA is highly polymorphic and S. aureus strains encode multiple tsaI homologues at the tspA locus, suggestive of additional roles in intra-species competition. In agreement, we demonstrate TspA-dependent growth inhibition of RN6390 by strain COL in the zebrafish infection model that is alleviated by the presence of TsaI homologues.

Publication metadata

Author(s): Ulhuq FR, Gomes MC, Duggan G, Guo M, Mendonca C, Buchanan G, Chalmers JD, Cao Z, Kneuper H, Murdoch S, Thomson S, Strahl H, Trost M, Mostowy S, Palmer T

Publication type: Article

Publication status: Published

Journal: Proceedings of the National Academy of Sciences of the United States of America

Year: 2020

Volume: 117

Issue: 34

Pages: 20836-20847

Print publication date: 25/08/2020

Online publication date: 07/08/2020

Acceptance date: 07/07/2020

Date deposited: 21/07/2020

ISSN (print): 0027-8424

ISSN (electronic): 1091-6490

Publisher: National Academy of Sciences


DOI: 10.1073/pnas.2006110117

PubMed id: 32769205


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Funder referenceFunder name
... Wellcome Trust Senior Research Fellowship (206444/Z/17/Z), and the Lister Institute of Preventive Medicine.
M.T. was funded by the Medical Research Council UK through Grant MC_UU_12016/5.
Work in the S. Mostowy laboratory is supported by a European Research Council Consolidator Grant (772853 - ENTRAPMENT)...
This study was supported the Wellcome Trust; Investigator Award 110183/Z/15/Z (to T.P.);