Abstract
BackgroundCampylobacter jejuni and Campylobacter coli are major global causes of bacterial gastroenteritis. Whilst several individual colonisation and virulence factors have been identified, our understanding of their role in the transmission, pathogenesis and ecology of Campylobacter has been hampered by the genotypic and phenotypic diversity within C. jejuni and C. coli. Autotransporter proteins are a family of outer membrane or secreted proteins in Gram-negative bacteria such as Campylobacter, which are associated with virulence functions. In this study we have examined the distribution and predicted functionality of the previously described capC and the newly identified, related capD autotransporter gene families in Campylobacter.ResultsTwo capC-like autotransporter families, designated capC and capD, were identified by homology searches of genomes of the genus Campylobacter. Each family contained four distinct orthologs of CapC and CapD. The distribution of these autotransporter genes was determined in 5829 C. jejuni and 1347 C. coli genomes. Autotransporter genes were found as intact, complete copies and inactive formats due to premature stop codons and frameshift mutations. Presence of inactive and intact autotransporter genes was associated with C. jejuni and C. coli multi-locus sequence types, but for capC, inactivation was independent from the length of homopolymeric tracts in the region upstream of the capC gene. Inactivation of capC or capD genes appears to represent lineage-specific gene decay of autotransporter genes. Intact capC genes were predominantly associated with the C. jejuni ST-45 and C. coli ST-828 generalist lineages. The capD3 gene was only found in the environmental C. coli Clade 3 lineage. These combined data support a scenario of inter-lineage and interspecies exchange of capC and subsets of capD autotransporters.ConclusionsIn this study we have identified two novel, related autotransporter gene families in the genus Campylobacter, which are not uniformly present and exhibit lineage-specific associations and gene decay. The distribution and decay of the capC and capD genes exemplifies the erosion of species barriers between certain lineages of C. jejuni and C. coli, probably arising through co-habitation. This may have implications for the phenotypic variability of these two pathogens and provide opportunity for new, hybrid genotypes to emerge.
Highlights
Campylobacter jejuni and Campylobacter coli are major global causes of bacterial gastroenteritis
We identify a related family of autotransporters, CapD, that are related to, but distinct from CapC, and have determined the distribution, genotype associations and extent of gene decay of the capC and capD genes within the genus Campylobacter, focusing on C. jejuni and C. coli
In capC autotransporters, the poly-G tract is located upstream of the coding sequence in the putative promoter region whilst in the capD autotransporter family the poly-G tract is located in the coding sequence or is absent entirely (Fig. 1)
Summary
Campylobacter jejuni and Campylobacter coli are major global causes of bacterial gastroenteritis. C. jejuni and C. coli are common commensals of poultry [3] with broiler chickens being the primary reservoir accounting for up to 80% of human infection [4]. These organisms are common inhabitants of the gastrointestinal tract of other food producing animals such as cattle, pigs and sheep [5]. Other C. jejuni lineages exhibit a host-adapted population structure in which certain genotypes are associated with a particular host species or ecological niche [9]. Certain lineages of C. coli have been linked to the swine production environment as well as the non-agricultural, environmental niche [10]
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