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

Abstract

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.

Phage infection and sub-lethal antibiotic exposure mediateEnterococcus faecalistype VII secretion system dependent inhibition of bystander bacteria

“…Antibacterial properties of T7SS substrates have been demonstrated [26, 27, 40]. Here we provide evidence that mutation in the LXG toxin encoded by OG1RF_11121 abrogates phage induced T7SS dependent inhibition of bystander bacteria while expression of the downstream immunity gene OG1RF_11122 in T7SS targeted E. faecalis ΔpipV583 cells conferred partial protection from this inhibition.…”

“…T7SS encoded antibacterial toxins secreted by Gram positive bacteria influence intra- and interspecies antagonism [26, 27]. While a nuclease and a membrane depolarizing toxin produced by Staphylococcus aureus target closely related S. aureus strains [26, 40], Streptococcus intermedius exhibits T7SS dependent antagonism against a wide-array of Gram positive bacteria [27]. To determine the target range of E. faecalis OG1RF T7SS antibacterial activity, we measured the viability of a panel of VPE25 insensitive Gram positive and Gram negative bacteria in our co-culture assay (Fig.…”

Phage infection and sub-lethal antibiotic exposure mediate Enterococcus faecalis type VII secretion system dependent inhibition of bystander bacteria

“…While a nuclease and a membrane depolarizing toxin produced by Staphylococcus aureus target closely related S . aureus strains [ 26 , 40 ], Streptococcus intermedius exhibits T7SS dependent antagonism against a wide-array of Gram positive bacteria [ 27 ]. To determine the target range of E .…”

“…Antibacterial properties of T7SS substrates have been demonstrated [ 26 , 27 , 40 ]. Here we provide evidence that mutation in the LXG toxin encoded by OG1RF_11121 abrogates phage induced T7SS dependent inhibition of bystander bacteria while expression of the downstream immunity gene OG1RF_11122 in T7SS targeted E .…”

The conserved core component EsaA mediates bacterial killing by the type VIIb secretion system

“…In this class, T7SSb also contributes to pathogenicity, as it promotes abscess formation in Staphylococcus aureus infections [1][2][3][4] . However, a distingushing feature of the T7SSb is its recently discovered role in interbacterial competition [5][6][7][8][9] .…”