The role of PemIK (PemK/PemI) type II TA system from Klebsiella pneumoniae clinical strains in lytic phage infection

Abstract

Since their discovery, toxin-antitoxin (TA) systems have captivated the attention of many scientists. Recent studies have demonstrated that TA systems play a key role in phage inhibition. The aim of the present study was to investigate the role of the PemIK (PemK/PemI) type II TA system in phage inhibition by its intrinsic expression in clinical strains of Klebsiella pneumoniae carrying the lncL plasmid, which harbours the carbapenemase OXA-48 and the PemK/PemI TA system. Furthermore, induced expression of the system in an IPTG-inducible plasmid in a reference strain of K. pneumoniae ATCC10031 was also studied. The results showed that induced expression of the whole TA system did not inhibit phage infection, whereas overexpression of the pemK toxin prevented early infection. To investigate the molecular mechanism involved in the PemK toxin-mediated inhibition of phage infection, assays measuring metabolic activity and viability were performed, revealing that overexpression of the PemK toxin led to dormancy of the bacteria. Thus, we demonstrate that the PemK/PemI TA system plays a role in phage infection and that the action of the free toxin induces a dormant state in the cells, resulting in inhibition of phage infections.

Molecular analysis of the interactions between phages and the bacterial host Klebsiella pneumoniae

“…This is a very interesting finding, as phage vB_KpnM-VAC36 did not successfully infect strain K3320. The fundamental role played by TA systems in the inhibition of phage infection has recently been demonstrated (20,(70)(71)(72). Interestingly, an inhibitor of the TA system (protein ID: QZE51102.1) was found in the genome of the phage vB_KpnP-VAC1.…”

“…Thus, TEM studies revealed that fifteen phages Moreover, four (vB_KpnM-VAC13 [37], vB_KpnM-VAC25, vB_KpnM-VAC36 and vB_KpnM-VAC66 [38]) were found to be members of the family Myoviridae, which is characterized by an icosahedral capsid and a rigid, contractile tail. Finally, only two phages were identified as members of the family Podoviridae, characterized by a small, non-contractile tail (vB_KpnP-VAC1 [20] and vB_KpnP-VAC71) (Figure 1B).…”

“…Ten new lytic phages isolated from sewage water samples and twelve lytic phages previously isolated by our research group (20,37,38) were used in this study. Briefly, 50 mL samples of water were collected near sewage plants and held at room temperature until processing in the laboratory.…”

“…Phages can also use the Toxin-Antitoxin (TA) systems, characterized by adjacent genes, generally consisting of two components: a stable toxin and an unstable antitoxin. The unstable component is degraded under stress conditions by the protease system, leading to toxin activation and often resulting in reduced bacterial metabolism and phage inhibition (19, 20). Bacteria can also employ other types of systems to cleave phage DNA, such as the restriction-modification (RM) system, which is characterized by an endonuclease protein that protects the bacterial cell by cutting foreign DNA at specific points, and a cognate DNA methylase, which modifies and protects the host DNA (21).…”

Intestinal phages interact with bacteria and are involved in human diseases

“…For example, for the lncL plasmid of Klebsiella pneumoniae carrying the PemIK (PemK/PemI) Type II TA System, overexpression of PemK toxin results in bacterial dormancy. 66 To bypass the toxin, phages can encode antitoxins. 67 , 68 Antitoxins can compete for the same binding site of toxins to disable their function.…”