The Mosaic Type IV Secretion Systems

Abstract

Escherichia coli and other Gram-negative and -positive bacteria employ type IV secretion systems (T4SSs) to translocate DNA and protein substrates, generally by contact-dependent mechanisms, to other cells. The T4SSs functionally encompass two major subfamilies, the conjugation systems and the effector translocators. The conjugation systems are responsible for interbacterial transfer of antibiotic resistance genes, virulence determinants, and genes encoding other traits of potential benefit to the bacterial host. The effector translocators are used by many Gram-negative pathogens for delivery of potentially hundreds of virulence proteins termed effectors to eukaryotic cells during infection. In E. coli and other species of Enterobacteriaceae, T4SSs identified to date function exclusively in conjugative DNA transfer. In these species, the plasmid-encoded systems can be classified as the P, F, and I types. The P-type systems are the simplest in terms of subunit composition and architecture, and members of this subfamily share features in common with the paradigmatic Agrobacterium tumefaciens VirB/VirD4 T4SS. This review will summarize our current knowledge of the E. coli systems and the A. tumefaciens P-type system, with emphasis on the structural diversity of the T4SSs. Ancestral P-, F-, and I-type systems were adapted throughout evolution to yield the extant effector translocators, and information about well-characterized effector translocators also is included to further illustrate the adaptive and mosaic nature of these highly versatile machines.

Spreading Patterns of NDM-Producing Enterobacteriaceae in Clinical and Environmental Settings in Yangon, Myanmar

“…IncFII-and IncX3-type plasmids employ different types of type IV secretion machinery for plasmid transfer. IncFII-type plasmid possesses F-type conjugative pilus, while IncX3-type plasmid harbors P-type pilus homologous to Agrobacterium tumefaciens VirB/VirD4 (24). While F-type pili are typically long and flexible, P-type pili are thicker and more rigid; thus, the difference in physical properties of conjugative pilus might be related to temperature sensitivity of plasmid transfer.…”

Horizontal Dissemination of Antimicrobial Resistance Determinants in Multiple Salmonella Serotypes following Isolation from the Commercial Swine Operation Environment after Manure Application

“…The T4SS in Gram-negative bacteria functionally encompass the conjugation system and the effector translocators for interbacterial transfer of AMR genes, virulence determinants, and genes encoding other traits beneficial to the host (67). IncN plasmids (pS6 to pS8) and IncI1 plasmids (pS9 [100-kb] and pS20) employed TraJ, which the has ability to conjugate, and the conjugation process could be stimulated approximately 100-fold, demonstrating functional conservation of a significant regulatory feature of F-like conjugation modules (68).…”

Use of chimeric type IV secretion systems to define contributions of outer membrane subassemblies for contact‐dependent translocation

“…The bacterial type IV secretion systems (T4SSs) are a highly versatile superfamily of macromolecular transporters (Costa et al, 2015;Christie, 2016). An early review highlighted this versatility by comparing three members of a subfamily of the T4SSs now termed the P-type or type IVa systems: (i) the Escherichia coli pKM101 Tra system, which mediates conjugative DNA transfer between bacteria, (ii) the Agrobacterium tumefaciens VirB/VirD4 system responsible for delivery of oncogenic T-DNA and effector proteins to plant cells and (iii) the Bordetella pertussis Ptl system that drives export of the multisubunit pertussis toxin (PT) across the B. pertussis outer membrane to the milieu (Winans et al, 1996).…”