Comparative genomics of all three Campylobacter sputorum biovars and a novel cattle-associated C. sputorum clade

Authors: Miller, William - Bill; Yee, Emma; Chapman, Mary; Bono, James - Jim

Submitted to: Genome Biology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2017
Publication Date: 6/19/2017
Citation: Miller, W.G., Yee, E., Chapman, M.H., Bono, J.L. 2017. Comparative genomics of all three Campylobacter sputorum biovars and a novel cattle-associated C. sputorum clade. Genome Biology and Evolution. 9(6): 1513-1518.

Interpretive Summary: Campylobacter sputorum is one of several campylobacters isolated from food animals, such as cattle and sheep. Campylobacter sputorum has also been shown to cause human illness, although C. sputorum-associated disease is infrequent and sporadic. The true prevalence of this species in food animals and its epidemiology in humans is not known, since C. sputorum is not well-understood, with few available molecular tests to identify these organisms. Three varieties of C. sputorum currently exist, and are sorted according to two biochemical tests. These varieties are biovars sputorum, fecalis and paraureolyticus. These varieties inhabit the same food animals; however, little is known about differences between these varieties beyond their reactions to the two biochemical tests. Additionally, another C. sputorum was isolated from cattle, and although these strains are biochemically of the fecalis variety, it is likely that these strains represent a fourth type of C. sputorum. To further characterize this species, the chromosomal DNA sequences of four strains representing the four C. sputorum types were determined. Comparative analysis indicated that the gene content of the four strains was remarkably similar and that the gene order on the chromosome was conserved among the four strains. Nevertheless, significant differences in gene content were observed among the three described C. sputorum varieties and it is likely that the fourth variety, composed of the cattle-associated strains, represents a new C. sputorum subspecies.

Technical Abstract: Campylobacter sputorum is a non-thermotolerant campylobacter that is primarily isolated from food animals such as cattle and sheep. C. sputorum is also infrequently associated with human illness. Based on catalase and urease activity, three biovars are currently recognized within C. sputorum: bv. sputorum (catalase negative, urease negative), bv. fecalis (catalase positive, urease negative), and bv. paraureolyticus (catalase negative, urease positive). A multi-locus sequence typing (MLST) method was recently constructed for C. sputorum. MLST typing of several cattle-associated C. sputorum isolates suggested that these strains are members of a divergent C. sputorum clade. Although catalase positive, and thus technically bv. fecalis, the taxonomic position of these strains could not be determined solely by MLST. To further characterize C. sputorum, the genomes of four strains representing all three biovars and the divergent clade were sequenced to completion. Here we present a comparative genomic analysis of the four C. sputorum genomes. This analysis indicates that the three biovars and the cattle-associated strains are highly-related at the genome level with similarities in gene content. Furthermore, the four genomes are strongly syntenic with one or two minor inversions. However, substantial differences in gene content were observed among the three biovars. Finally, although the strain representing the cattle-associated isolates was shown to be C. sputorum, it is possible that this strain is a member of a novel C. sputorum subspecies; thus, these cattle-associated strains may form a second taxon within C. sputorum.