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. 2016 Jul 2;8(6):2006-19.
doi: 10.1093/gbe/evw146.

Comparative Genomics of Campylobacter Fetus From Reptiles and Mammals Reveals Divergent Evolution in Host-Associated Lineages

Free PMC article

Comparative Genomics of Campylobacter Fetus From Reptiles and Mammals Reveals Divergent Evolution in Host-Associated Lineages

Maarten J Gilbert et al. Genome Biol Evol. .
Free PMC article


Campylobacter fetus currently comprises three recognized subspecies, which display distinct host association. Campylobacter fetus subsp. fetus and C fetus subsp. venerealis are both associated with endothermic mammals, primarily ruminants, whereas C fetus subsp. testudinum is primarily associated with ectothermic reptiles. Both C. fetus subsp. testudinum and C. fetus subsp. fetus have been associated with severe infections, often with a systemic component, in immunocompromised humans. To study the genetic factors associated with the distinct host dichotomy in C. fetus, whole-genome sequencing and comparison of mammal- and reptile-associated C fetus was performed. The genomes of C fetus subsp. testudinum isolated from either reptiles or humans were compared with elucidate the genetic factors associated with pathogenicity in humans. Genomic comparisons showed conservation of gene content and organization among C fetus subspecies, but a clear distinction between mammal- and reptile-associated C fetus was observed. Several genomic regions appeared to be subspecies specific, including a putative tricarballylate catabolism pathway, exclusively present in C fetus subsp. testudinum strains. Within C fetus subsp. testudinum, sapA, sapB, and sapAB type strains were observed. The recombinant locus iamABC (mlaFED) was exclusively associated with invasive C fetus subsp. testudinum strains isolated from humans. A phylogenetic reconstruction was consistent with divergent evolution in host-associated strains and the existence of a barrier to lateral gene transfer between mammal- and reptile-associated C fetus Overall, this study shows that reptile-associated C fetus subsp. testudinum is genetically divergent from mammal-associated C fetus subspecies.

Keywords: campylobacter fetus; comparative genomics; evolution; mammal; recombination; reptile.


Fig. 1.
Fig. 1.
BRIG plot of C. fetus. BLASTN-based genomic comparison of all Cft strains, including Cft strain 03-427 (reference genome), Cff strain 82-40, and Cfv strain 97/608. Cft strains isolated from humans are shown in blue; Cft strains isolated from reptiles are shown in green, with predicted Cft sapA strains shown in dark green and predicted Cft sapB and sapAB strains shown in light green; Cff is shown in yellow; and Cfv is shown in red. Characteristic genomic features of C. fetus and Cft in particular have been highlighted. Features containing only hypothetical proteins are not indicated.
Fig. 2.
Fig. 2.
Single-gene phylogeny of iamA (mlaF) for all strains examined. The recombinant invasive Cft strains isolated from humans are shown in bold.
Fig. 3.
Fig. 3.
Phylogenetic reconstruction of the C. fetus clade based on Gubbins. Recombination regions within the 781,293 nt gapless core genome alignment are indicated in red (similar recombination region in multiple strains) or blue (unique recombination region). Species and subspecies from top to bottom: C. iguaniorum, purple; C. hyointestinalis, dark blue; C. fetus subsp. testudinum (human strains), light blue; C. fetus subsp. testudinum (reptilian strains), dark green (sapA strains) or light green (sapB and sapAB strains); C. fetus subsp. fetus (based on genotype), yellow (sapB strains) or orange (sapA strains); C. fetus subsp. venerealis (based on genotype), red. For C. fetus, the sap type of the corresponding strains is indicated with A, B, or AB. To increase the intraspecies resolution for C. fetus, the branches of the dendrogram are truncated for C. hyointestinalis and C. iguaniorum. Recombination regions of interest have been highlighted.

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