A membrane-depolarizing toxin substrate of the Staphylococcus aureus type VII secretion system mediates intraspecies competition

Fatima R. Ulhuq, Margarida C. Gomes, Gina M. Duggan, Manman Guo, Chriselle Mendonca, Grant Buchanan, James D. Chalmers, Zhenping Cao, Holger Kneuper, Sarah Murdoch, Sarah Thomson, Henrik Strahl, Matthias Trost, Serge Mostowy (Lead / Corresponding author), Tracy Palmer (Lead / Corresponding author)

Research output: Contribution to journalArticlepeer-review

31 Citations (Scopus)
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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 coproduction 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 homologs at the tspA locus, suggestive of additional roles in intraspecies 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 homologs.

Original languageEnglish
Pages (from-to)20836-20847
Number of pages12
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number34
Early online date7 Aug 2020
Publication statusPublished - 25 Aug 2020


  • type VII secretion system
  • Staphylococcus aureus
  • zebrafish
  • membrane-depolarizing toxin
  • bacterial competition
  • Bacterial competition
  • Type VII secretion system
  • Zebrafish
  • Membrane-depolarizing toxin

ASJC Scopus subject areas

  • General


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