Complete genome sequence of the hippuricase-positive Campylobacter avium type strain LMG 24591

Authors: Miller, William - Bill; Chapman, Mary; Yee, Emma; REVEZ, JOANA - European Centre For Disease Control And Prevention; Bono, James - Jim; ROSSI, MIRKO - University Of Helsinki

Submitted to: Genome Announcements
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2017
Publication Date: 10/26/2017
Citation: Miller, W.G., Chapman, M.H., Yee, E., Revez, J., Bono, J.L., Rossi, M. 2017. Complete genome sequence of the hippuricase-positive Campylobacter avium type strain LMG 24591. Genome Announcements. 5(43):e01221-17. https://doi.org/10.1128/genomeA.01221-17.
DOI: https://doi.org/10.1128/genomeA.01221-17

Interpretive Summary: Campylobacter species are isolated typically from a wide variety of warm-blooded animals and birds. Species, such as the human pathogenic C. jejuni and C. coli are typically isolated from chickens and turkeys. Recently, a novel Campylobacter, C. avium, was also isolated from poultry. This study determined the chromosomal sequence for two C. avium strains, both from broiler chickens. The gene content and genetic features of these two strains were highly similar to those of other poultry-associated campylobacters. However, some genes were notably absent, which might confer lower virulence and higher oxygen sensitivity upon C. avium. Additionally, C. avium was predicted to be defective in selenium metabolism, a trait seen in some Campylobacter species isolated from large grazing or foraging animals. C. avium can hydrolyze hippuric acid. This is significant because, until the description of C. avium, the primary Campylobacter pathogen C. jejuni was the only Campylobacter thought to hydrolyze hippuric acid; thus, clinical labs would test for the presence of this pathogen using a simple colorimetric hippuricase assay. The C. jejuni hippuricase HipO was not detected in C. avium. However, this study demonstrated experimentally that C. avium contains an alternate hippuricase, which we have called HipA. Although C. avium could be potentially confused with C. jejuni in poultry or clinical samples, due to identical positive hippuricase reactions, the low similarity between HipO and HipA would steer identification of these two Campylobacter species towards more molecular-based methodologies.

Technical Abstract: Campylobacter avium is a hippurate-positive, thermotolerant campylobacter that has been isolated from poultry. Here we present the genome sequences of two C. avium strains isolated from broiler chickens: strains LMG 24591T (complete genome) and LMG 24592 (draft genome). The C. avium type strain genome contains 40 hypervariable G:C tracts and many genes identified previously in the genomes of related Campylobacter spp. However, C. avium does not encode CadF, the ferredoxins FdxA and FdxB, methionine sulfoxide reductase or the 14 subunit (Nuo) NADH:quinone oxidoreductase I. Moreover, the C. avium genomes do not encode any proteins associated with selenium metabolism, such as: selenoproteins, the selenocysteinyl tRNA and the selenocysteine insertion machinery. A similar defect in selenium metabolism was observed previously in C. lanienae and C. lanienae-related Campylobacter spp. Although C. avium is hippuricase positive, no gene orthologous to C. jejuni hipO was identified in either C. avium genome. Candidate hippuricase genes with domains similar to hipO were cloned into Escherichia coli; one gene, termed hipA, conferred strong hippuricase activity. Therefore, Campylobacter encodes two functionally-equivalent but unrelated hippuricases: HipO, identified in C. jejuni and C. hepaticus; and HipA, identified in C. avium. Orthologs with approx. 73% similarity to HipA were also found in C. jejuni and C. coli, but these proteins do not possess any hippuricase activity, suggesting that the HipA orthologs have either gained or lost function through the accumulation of critical amino acid changes.