Abstract
Campylobacter transducer-like proteins (Tlps), also known as methyl-accepting chemotaxis proteins (MCPs), are associated with virulence as well as niche and host adaptation. While functional attributes of these proteins are being elucidated, little has been published regarding their sequence diversity or chromosomal locations and context, although they appear to define invertible regions within Campylobacter jejuni genomes. Genome assemblies for several species of Campylobacter were obtained from the publicly available NCBI repositories. Genomes from all isolates were obtained from GenBank and assessed for Tlp content, while data from isolates with complete, finished genomes were used to determine the identity of Tlps as well as the gene content of putative invertible elements (IEs) in C. jejuni (Cj) and C. coli (Cc). Tlps from several Campylobacter species were organized into a nomenclature system and novel Tlps were defined and named for Cj and Cc. The content of Tlps appears to be species-specific, though diverse within species. Cj and Cc carried overlapping, related Tlp content, as did the three C. fetus subspecies. Tlp1 was detected in 88% of Cj isolates and approximately 43% of Cc, and was found in a different conserved chromosomal location and genetic context in each species. Tlp1 and Tlp 3 predominated in genomes from Cj whereas other Tlps were detected less frequently. Tlp13 and Tlp20 predominated in genomes from Cc while some Cj/Cc Tlps were not detected at all. Tlps 2–4 and 11–20 were less frequently detected and many showed sequence heterogeneity that could affect substrate binding, signal transduction, or both. Tlps other than Tlp1, 7, and 10 had substantial sequence identity in the C-terminal half of the protein, creating chromosomal repeats potentially capable of mediating the inversion of large chromosomal DNA. Cj and Cc Tlps were both found in association with only 14 different genes, indicating a limited genomic context. In Cj these Tlps defined IEs that were for the most part found at a single chromosomal location and comprised of a conserved set of genes. Cc IEs were situated at very different chromosomal locations, had different structures than Cj IEs, and were occasionally incomplete, therefore not capable of inversion. Tlps may have a role in Campylobacter genome structure and dynamics as well as acting as chemoreceptors mediating chemotactic responses.
Highlights
Campylobacter spp. are critically important pathogenic bacteria often introduced into human populations through consumption of contaminated food or water
Group A transducer-like proteins (Tlps) with different ligand sensing/small molecule binding domains are frequently classified according to their ligand-binding capability, allowing them to be distinguished from each other by amino acid sequence differences in the N-terminal half of the protein [10]
Protein FASTA files were obtained for Tlps from each of the 80 strains (11 Campylobacter species) included in this analysis and were used to generate a UPGMA dendrogram that shows the relationships of protein sequences without corrections for evolutionary models (Fig 1)
Summary
Campylobacter spp. are critically important pathogenic bacteria often introduced into human populations through consumption of contaminated food or water. C. jejuni (Cj) and C. coli (Cc) are among the most frequently isolated causes of food- and water-borne gastroenteritis in developed and developing nations [1,2,3,4]. They have been isolated from a wide range of animal sources, including cattle, pigs, birds, pets, and poultry, with poultry being the most commonly identified source of human infection, though this has been contested [3,5]. Campylobacteriosis has a very high population burden of illness and is a costly public health issue for which the benefit:cost ratio of intervention to reduce cases is extremely high [10]
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