Substrate Interaction with the EssC Coupling Protein of the Type VIIb Secretion System

Staphylococcus aureus employs the type VIIb secretion system T7SSb to secrete effector proteins that either have antibacterial activities or promote bacterial persistence in mouse infection models. Here, we present the crystal structure of the ATPase domain D3 of the EssC coupling protein from S. aureus USA300FPR3757, an integral component of the T7SSb complex, resolved at a 1.7 resolution. EssC D3 shares structural homology with FtsK SpoIII like ATPase domains of T7SSa and T7SSb and exhibits a conserved pocket on the surface with differential amino acid composition. In T7SSa, substrate EsxB interacts with the D3 domain through this pocket. Here, we identify amino acids in this pocket that are essential for effector protein secretion in the T7SSb. Our results reveal that the adjacent ATPase domain D2 is a substrate binding site on EssC and that substrates bound to D2 require domain D3 for further transport. Point mutations in the Walker B motif of domain D3 have diametric effects on secretion activity, either abolishing or boosting it, pointing to a critical role of domain D3 in the substrate transport. Finally, we identify ATPase domain D3 as a virulence determinant of S. aureus USA300FPR3757 using an invertebrate in vivo infection mode

The extracellular matrix protects Bacillus subtilis colonies from Pseudomonas invasion and modulates plant co-colonization.

Bacteria of the generaPseudomonasandBacilluscan promote plant growth and protect plantsfrom pathogens. However, the interactions between these plant-beneficial bacteria areunderstudied. Here, we explore the interaction betweenBacillus subtilis3610 andPseudomonaschlororaphisPCL1606. We show that the extracellular matrix protectsB. subtiliscolonies frominfiltration byP. chlororaphis. The absence of extracellular matrix results in increasedfluidityand loss of structure of theB. subtiliscolony. TheP. chlororaphistype VI secretion system(T6SS) is activated upon contact withB. subtiliscells, and stimulatesB. subtilissporulation.Furthermore, wefind thatB. subtilissporulation observed prior to direct contact withP.chlororaphisis mediated by histidine kinases KinA and KinB. Finally, we demonstrate theimportance of the extracellular matrix and the T6SS in modulating the coexistence of the twospecies on melon plant leaves and seed