Campylobacter molothri sp. nov. isolated from wild birds

Abstract

Twenty-nine hippuricase-positive Campylobacter strains were isolated from wild birds and river water. Previous characterization using atpA typing indicated that these strains were related to Campylobacter jejuni and Campylobacter coli but were most similar to three recently described hippuricase-positive Campylobacter species recovered from zebra finches, i.e. C. aviculae, C. estrildidarum and C. taeniopygiae. Phylogenetic analyses using 330 core genes placed the 29 strains into a clade well separated from the other Campylobacter taxa, indicating that these strains represent a novel Campylobacter species. Pairwise digital DNA-DNA hybridization and average nucleotide identity values were below 70 and 95 %, respectively, thus providing further supporting evidence of a novel taxon. Standard phenotypic testing was performed. All strains are microaerobic or anaerobic, motile, Gram-negative, spiral cells that are oxidase, catalase and nitrate reductase positive, but urease negative. Genomic analyses indicate that the 29 strains can potentially synthesize very few amino acids de novo and are auxotrophic for many amino acids and cofactors, similar to the species composing the Campylobacter lari group. In addition, these strains encode complete Entner-Doudoroff and Leloir pathways, suggesting that they may possess the ability to utilize both glucose and galactose; these pathways were also identified in the genomes of the zebra finch-associated taxa. The data presented here show that these strains represent a novel species within Campylobacter, for which the name Campylobacter molothri sp. nov. (type strain RM10537^T=LMG 32306^T=CCUG 75331^T) is proposed.

Keywords: Campylobacter; blackbird; brown-headed cowbird; hippuricase; novel species.

Fig. 1.. Scanning electron micrograph images of Campylobacter molothri sp. nov. (a) Campylobacter molothri sp. nov. RM10537^T (=LMG 32306^T) and (b) Campylobacter molothri sp. nov. RM12397 (=LMG 32307) at ×5000 magnification.

Fig. 2.. 16S rRNA gene sequence phylogenetic tree representing Campylobacter molothri sp. nov. and the Campylobacter taxa type strains. 16S rRNA gene accession numbers are appended parenthetically to each node. Bootstrap values >75 % are shown next to the branches. The scale bar represents the number of base substitutions per site. The 16S rRNA gene sequence of the Helicobacter pylori type strain was used to root the tree. The 16S rRNA gene sequences of strains W0045, W0047 and RM17709 have 3, 1 and 1 SNPs relative to the 16S rRNA gene sequence of Campylobacter molothri sp. nov. RM10537^T; the 16S rRNA gene sequences of the remaining Campylobacter molothri sp. nov. strains are identical to those of the type strain and are not included in the dendrogram.

Fig. 3.. Core-genome phylogenetic tree representing Campylobacter molothri sp. nov. and the Campylobacter taxa type strains. Bootstrap values >75 % are shown at the nodes. The Helicobacter pylori type strain core gene sequences were concatenated and used in the alignment to root the tree. The scale bar represents the number of base substitutions per site.