Identification of a Functional Type VI Secretion System in Campylobacter jejuni Conferring Capsule Polysaccharide Sensitive Cytotoxicity

Abstract

The pathogen Campylobacter jejuni is the principal cause of bacterial food-borne infections. The mechanism(s) that contribute to bacterial survival and disease are still poorly understood. In other bacterial species, type VI secretion systems (T6SS) are increasingly recognized to contribute to bacterial pathogenesis by toxic effects on host cells or competing bacterial species. Here we report the presence of a functional Type VI secretion system in C. jejuni. Proteome and genetic analyses revealed that C. jejuni strain 108 contains a 17-kb T6SS gene cluster consisting of 13 T6SS-conserved genes, including the T6SS hallmark genes hcp and vgrG. The cluster lacks an ortholog of the ClpV ATPase considered important for T6SS function. The sequence and organization of the C. jejuni T6SS genes resemble those of the T6SS located on the HHGI1 pathogenicity island of Helicobacter hepaticus. The C. jejuni T6SS is integrated into the earlier acquired Campylobacter integrated element CJIE3 and is present in about 10% of C. jejuni isolates including several isolates derived from patients with the rare clinical feature of C. jejuni bacteremia. Targeted mutagenesis of C. jejuni T6SS genes revealed T6SS-dependent secretion of the Hcp needle protein into the culture supernatant. Infection assays provided evidence that the C. jejuni T6SS confers contact-dependent cytotoxicity towards red blood cells but not macrophages. This trait was observed only in a capsule-deficient bacterial phenotype. The unique C. jejuni T6SS phenotype of capsule-sensitive contact-mediated hemolysis represents a novel evolutionary pathway of T6SS in bacteria and expands the repertoire of virulence properties associated with T6SS.

Helicobacter pullorum Isolated from Fresh Chicken Meat: Antibiotic Resistance and Genomic Traits of an Emerging Foodborne Pathogen

“…The presently characterized T6SS consists of 13 noncontiguous genes, including the hallmark hcp and vgrG genes, and closely resembles the T6SS genes of C. jejuni at both gene organization and content levels (Fig. 3) (40). The existence of a putative functional T6SS in H. pullorum was recently proposed by Sirianni et al, who correlated the mechanism of action of this cluster with the transcellular invasion of Caco-2 intestinal epithelial cells by this pathogen (41).…”

“…The existence of a putative functional T6SS in H. pullorum was recently proposed by Sirianni et al, who correlated the mechanism of action of this cluster with the transcellular invasion of Caco-2 intestinal epithelial cells by this pathogen (41). In C. jejuni, the prevalence of the T6SS varies greatly among isolates and appears to depend on the geographic origin of the strain, being more prevalent among strains from Asia (from 60.6% to 71.5%) than those from Western countries (Ͻ10%) (40,42). In addition, the T6SS is associated with more severe forms of C. jejuni infection, such as bloody diarrhea and bacteremia, supporting the contribution of the system to the virulence of this pathogen (40,42).…”

“…In C. jejuni, the prevalence of the T6SS varies greatly among isolates and appears to depend on the geographic origin of the strain, being more prevalent among strains from Asia (from 60.6% to 71.5%) than those from Western countries (Ͻ10%) (40,42). In addition, the T6SS is associated with more severe forms of C. jejuni infection, such as bloody diarrhea and bacteremia, supporting the contribution of the system to the virulence of this pathogen (40,42). Therefore, the presence of a complete and most likely functional T6SS in three out of the four H. pullorum isolates suggests that this system is common among this species, constituting an important virulence mechanism.…”

Characterisation of Aerotolerant Forms of a Robust Chicken Colonizing Campylobacter coli

“…Bronnec et al (2016) identified a complete type VI secretion system in C. jejuni Bf and suggested that it may contribute to the aerotolerant phenotype. The C. coli OR12 genome contains a complete T6SS, although C. coli RM2228, which did not demonstrate aerotolerance, also possesses a full T6SS (Bleumink-Pluym et al, 2013). This would suggest that possession of T6SS alone does not confer aerotolerance, although it could be involved when in combination with other features.…”

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

“…Our results are consistent with findings in other bac- terial pathogens of the role of T6SS in adherence and cytotoxicity to host cells. It has been reported that the T6SS in APEC is involved in adherence to host cells (46), the Bordetella bronchiseptica T6SS mediates cytotoxicity in murine macrophages (47), and the Campylobacter jejuni T6SS confers cytotoxicity to red blood cells (48). Since FliC contributes to cytotoxicity (49), it is possible that the T6SS of CF74 contributes to the apoptotic death of host cells in vitro indirectly by affecting the production and secretion of FliC.…”