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Culture-independent genomics of a novel chlamydial pathogen of fish provides new insight into host-specific adaptations utilized by these intracellular bacteria

Taylor-Brown, A, Pillonel, T, Bridle, A ORCID: 0000-0002-5788-1297, Qi, W, Bachmann, NL, Miller, TL, Greub, G, Nowak, B ORCID: 0000-0002-0347-643X, Seth-Smith, HMB, Vaughan, L and Polkinghorne, A 2017 , 'Culture-independent genomics of a novel chlamydial pathogen of fish provides new insight into host-specific adaptations utilized by these intracellular bacteria' , Environmental Microbiology, vol. 19, no. 5 , pp. 1899-1913 , doi:

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Several Chlamydiales families are associated with epitheliocystis, a common condition of the fish gill epithelium. These families share common ancestors with the Chlamydiaceae and environmental Chlamydiae. Due to the lack of culture systems, little is known about the biology of these chlamydial fish pathogens. We investigated epitheliocystis in cultured Orange-spotted grouper (Epinephelus coioides) from North Queensland, Australia. Basophilic inclusions were present in the gills of 22/31 fish and the presence of the chlamydial pathogen in the cysts was confirmed by in situ hybridization. Giant grouper (Epinephelus lanceolatus) cultured in the same systems were epitheliocystis free. 16S rRNA gene sequencing revealed a novel member of the Candidatus Parilichlamydiaceae: Ca. Similichlamydia epinephelii. Using metagenomic approaches, we obtained an estimated 68% of the chlamydial genome, revealing that this novel chlamydial pathogen shares a number of key pathogenic hallmarks with the Chlamydiaceae, including an intact Type III Secretion system and several chlamydial virulence factors. This provides additional evidence that these pathogenic mechanisms were acquired early in the evolution of this unique bacterial phylum. The identification and genomic characterization of Ca. S. epinephelii provides new opportunities to study the biology of distantly-related chlamydial pathogens while shining a new light on the evolution of pathogenicity of the Chlamydiaceae.

Item Type: Article
Authors/Creators:Taylor-Brown, A and Pillonel, T and Bridle, A and Qi, W and Bachmann, NL and Miller, TL and Greub, G and Nowak, B and Seth-Smith, HMB and Vaughan, L and Polkinghorne, A
Keywords: chlamydial pathogen, genome, fish
Journal or Publication Title: Environmental Microbiology
Publisher: Blackwell Publishing Ltd
ISSN: 1462-2912
DOI / ID Number:
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Copyright 2017 Society for Applied Microbiology and John Wiley & Sons Ltd

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