Telocins (TelA-TelE) are bacteriocin-type antibacterial toxins encoded by telomere bacteriophages - identified in Klebsiella species - that enable their bacterial hosts to kill competitor strains. To exert toxic activity, telocins must be imported by the competitor cells. This, in turn, means that there must be a means for telocins to be secreted by the Klebsiella species that produces them. Defining how these proteins are secreted is therefore essential for explaining how these antibacterial proteins are deployed and how they function as ecological effectors in microbial communities.
Protein secretion in bacterial cells is an active and non-destructive process mediated by diverse protein secretion systems. The protein secretion systems present in Klebsiella are of the type I (T1SS), type II (T2SS), and type VI (T6SS) systems. To determine and annotate the genes encoding these three secretion systems, two relevant strains: Klebsiella pneumoniae AJ218 and Klebsiella variicola AJ292, were assessed by bioinformatic analyses, including homology searches based on conserved secretion-system components and gene-cluster mapping, providing a framework to assess which of these systems contribute to telocin release. Building on this framework, we aim to determine which host-encoded secretion machinery mediates telocin export in Klebsiella pneumoniae AJ218 and Klebsiella variicola AJ292. To address this, we will construct targeted loss-of-function mutants in the aforementioned secretion systems and compare TelA release between secretion-system mutants and wild-type strains using inducible telocin expression. This approach is being extended to additional telocins (TelB-TelE) to assess whether different telocin classes utilise shared or distinct secretion machineries. Available structural information will be used to determine the spatial constraints for T1SS, T2SS and T6SS to span the peptidoglycan cell-wall and the inner and outer membranes to function, including whether their molecular dimensions are compatible with passage of the telocins and how these secretion systems are spatially organised within the cell.