Identification of a Campylobacter jejuni‐secreted protein required for maximal invasion of host cells

Abstract

The food-borne pathogen Campylobacter jejuni is dependent on a functional flagellum for motility and the export of virulence proteins that promote maximal host cell invasion. Both the flagellar and non-flagellar proteins exported via the flagellar type III secretion system contain a sequence within the amino-terminus that directs their export from the bacterial cell. Accordingly, we developed a genetic screen to identify C. jejuni genes that encode a type III secretion amino-terminal sequence that utilizes the flagellar type III secretion system of Yersinia enterocolitica and a phospholipase reporter (yplA). We screened a library of 321 C. jejuni genes and identified proteins with putative type III secretion amino-terminal sequences. One gene identified by the screen was Cj1242. We generated a mutation in Cj1242, and performed growth rate, motility, secretion and INT 407 cell adherence and internalization assays. The C. jejuni Cj1242 mutant was not altered in growth rate or motility when compared with the wild-type strain, but displayed an altered secretion profile and a reduction in host cell internalization. Based on the phenotype of the C. jejuni Cj1242 mutant, we designated the protein Campylobacter invasion antigen C (CiaC). Collectively, our findings indicate that CiaC is a potentially important virulence factor.

Extracellular secretion of protease HtrA fromCampylobacter jejuniis highly efficient and independent of its protease activity and flagellum

“…A series of papers reported on the extracellular release of C. jejuni proteins into the medium in the presence of fetal calf serum (FCS) or upon host cell contact, which was abrogated when certain fl agellar genes were mutated. This led some groups to propose that the C. jejuni fl agellum may act as a classical type III secretion system (T3SS) for the extracellular transport or injection of proteins, which then infl uence bacterial-host interactions [10][11][12][13]. The fi rst identifi ed secreted factor depending on the fl agellum was the Campylobacter invasion antigen B (CiaB), a 73-kDa protein with weak homology to T3SS effectors of other pathogens [11].…”

Is theCampylobacter jejunisecretory protein Cj0069 a suitable antigen for serodiagnostics?

“…The secreted proteins identified by Christensen and coworkers [8] have probably a high immunogenic potential due to their exposure to the human immune system and should therefore be capable of developing highly sensitive and specific serological tests.…”

“…In addition, secretion of Cias could be induced by fetal bovine serum [25]. Christensen and coworkers examined genes by in silico analysis on properties characterizing potentially secretory Campylobacter proteins, such as transmembrane and periplasmic domains, as well as Sec-or twin-arginine translocation (Tat)-motifs [8]. All proteins secreted via a T3SS, or its flagellar homolog, have a specific sequence motif at their Nterminal end.…”

“…Thus, Y. enterocolitia proved to be a suitable model system to screen for C. jejuni secretory proteins and consequently brought 42 secretory proteins to light. The function of most of them is still unknown [8].…”

“…Based on the published list of secreted proteins by Christensen and coworkers [8], three of them were selected randomly according to an easily distinguishable molecular weight. The complete sequenced and well-characterized strain C. jejuni NCTC 11168 was used as genomic DNA template for the amplification of the respective genes.…”