Intraspecies Competition in Serratia marcescens Is Mediated by Type VI-Secreted Rhs Effectors and a Conserved Effector-Associated Accessory Protein.
Bottom Line: Multiple antibacterial effectors can be delivered by these systems, with diverse activities against target cells and distinct modes of secretion.Polymorphic toxins containing Rhs repeat domains represent a recently identified and as-yet poorly characterized class of T6SS-dependent effectors.Furthermore, a new family of accessory proteins associated with T6SS effectors has been identified, exemplified by S. marcescens EagR1, which is specifically required for deployment of its associated Rhs effector.
Affiliation: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, United Kingdom.Show MeSH
Related in: MedlinePlus
Mentions: Having shown that Rhs1 and Rhs2 of S. marcescens Db10 are T6SS-delivered toxins, we asked what contribution they make toward T6SS-mediated antibacterial activity against competitor organisms. First, we used three non-Serratia species, Pseudomonas fluorescens, Escherichia coli, and Enterobacter cloacae, as targets (Fig. 4A). Against P. fluorescens, single Δrhs1 and Δrhs2 and double Δrhs1 Δrhs2 mutant attackers showed a modest decrease in antibacterial activity. Against Escherichia coli, the Δrhs1 mutant was not impaired, whereas the Δrhs2 and Δrhs1 Δrhs2 mutants again showed a modest decrease in antibacterial activity. However, against both target organisms, even the Δrhs1 Δrhs2 mutant retained considerable killing activity, implying that other effectors make an important contribution. In contrast, the Δrhs1 Δrhs2 mutant was no longer able to inhibit Enterobacter cloacae, behaving indistinguishably from a ΔtssE (T6SS mutant) attacker, with most of the effect attributable to Rhs2. Therefore, Rhs2 is the primary effector acting against this target organism. Enterobacter cloacae is closely related to S. marcescens and has a similar T6SS; therefore, we examined the contribution of Rhs to the ability of S. marcescens Db10 to compete with even more closely related targets, namely, other strains of S. marcescens (Fig. 4B). Against S. marcescens SM39, the Δrhs1 Δrhs2 mutant of Db10 was completely attenuated, with the single Δrhs2 mutant also severely impaired. Against S. marcescens ATCC 274, the double Δrhs1 Δrhs2 mutant retained negligible antibacterial activity, and this time both single rhs mutants showed reduced activity.
Affiliation: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, United Kingdom.