Characterization of IcmF of the type VI secretion system in an avian pathogenic Escherichia coli (APEC) strain

Abstract

The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome-lysosome fusion in Legionella pneumophila. In Vibrio cholerae it is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcp and clpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenic Escherichia coli (APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenic E. coli (ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APEC icmF mutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. The icmF mutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in the icmF mutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.

The Type VI Secretion System Modulates Flagellar Gene Expression and Secretion in Citrobacter freundii and Contributes to Adhesion and Cytotoxicity to Host Cells

“…It has been reported that the ⌬icmF strain decreased the expression of flhC, flhD, flgM, and fliA flagellar genes at the level of transcription in avian-pathogenic E. coli (APEC) (15). Our results suggested that deletion of T6SS or its key genes was detrimental to the expression of the flagellar regulon at the level of transcription, as was found in E. coli (15).…”

“…It has been reported that the T6SS contributes to the virulence development of various pathogens and is often activated upon contact with target cells for the secretion of effector proteins (1)(2)(3)(4)(5)(6)(7)(14)(15)(16)(17). The expression and assembly of the T6SS are tightly controlled at both the transcriptional and posttranscriptional levels (12,13,18).…”

“…The expression and assembly of the T6SS are tightly controlled at both the transcriptional and posttranscriptional levels (12,13,18). Furthermore, the IcmF protein of the T6SS has been shown to be involved in flagellar regulation and affects motility and biofilm formation (15). The flagellum is composed of a basal body, a hook, and a filament.…”

“…ClpV is a member of the AAA ϩ (ATPases associated with various cellular activities) protein family (8,11). It forms oligomeric complexes to energize the system for the secretion of effector proteins, which include the secreted VgrG (valine glycine repeat) and Hcp (hemolysin-coregulated protein) proteins (1,(12)(13)(14)(15)(16)(17).…”

Phytobacterial Type VI Secretion System - Gene Distribution, Phylogeny, Structure and Biological Functions

“…The cytosolic domain has a conserved Walker-A motif, indicating a function as an ATPase during secretion, consistent with the finding that IcmF mutations prevent Hcp secretion (Pukatzki et al, 2006;Zheng & Leung 2007). An icmF mutant of avian pathogenic E. coli had decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival and was also defective for biofilm formation on abiotic surfaces (Pace et al, 2011).…”