A Spirochaete is suggested as the causative agent of Akoya oyster disease by metagenomic analysis

• Published in: PloS one Vol. 12; no. 8; p. e0182280
• Main Authors: Matsuyama, Tomomasa, Yasuike, Motoshige, Fujiwara, Atushi, Nakamura, Yoji, Takano, Tomokazu, Takeuchi, Takeshi, Satoh, Noriyuki, Adachi, Yoshikazu, Tsuchihashi, Yasushi, Aoki, Hideo, Odawara, Kazushi, Iwanaga, Shunsuke, Kurita, Jun, Kamaishi, Takashi, Nakayasu, Chihaya
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 03.08.2017; Public Library of Science (PLoS)
• Subjects: Animal diseases; Animal Shells - microbiology; Animals; Antibiotics; Bacteria; Bacterial infections; Biology and Life Sciences; Black-lipped pearl oyster; Brachyspira; Browning; Causes of; Diagnosis; Disease transmission; Diseases and pests; Distribution; DNA - chemistry; DNA - isolation & purification; DNA - metabolism; Earth Sciences; Genes; Hemolymph; Hemolymph - microbiology; In Situ Hybridization, Fluorescence; Mantle; Medicine and Health Sciences; Metagenomics; Mortality; New species; Oysters; Pathogens; Pearls; Penicillin; Penicillins - pharmacology; Phylogeny; Pinctada - genetics; Pinctada fucata martensii; Research and Analysis Methods; RNA, Ribosomal, 16S - classification; RNA, Ribosomal, 16S - isolation & purification; RNA, Ribosomal, 16S - metabolism; rRNA 16S; Sequence Analysis, DNA; Soft tissues; Spirochaeta - classification; Spirochaeta - drug effects; Spirochaeta - pathogenicity; Spirochaetales Infections - genetics; Spirochaetales Infections - pathology; Spirochaetales Infections - veterinary; Spirochetes; Tissues; Japan; Okinawa
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0182280

Mass mortality that is acompanied by reddish browning of the soft tissues has been occurring in cultured pearl oyster, Pinctada fucata martensii. The disease is called Akoya oyster disease (AOD). Although spreading pattern of the disease and transmission experiments suggest that the disease is infectious, the causative agent has not yet been identified. We used shotgun and 16S rRNA-based metagenomic analysis to identify genes that are present specifically in affected oysters. The genes found only in diseased oysters were mostly bacterial origin, suggesting that the causative agent was a bacterial pathogen. This hypothesis was supported by the inhibition of AOD development in naïve oysters injected with the hemolymph of diseased animals followed immediately with penicillin bath-administration. Further analyses of the hemolymph and mantle specifically and universally detected genes of bacteria that belong to phylum Spirochaetes in diseased pearl oysters but not in healthy oysters. By in situ hybridization or immunostaining, a Brachyspira-like bacterium was observed in the smears of hemolymph from affected oysters, but not from healthy oysters. Phylogenetic analysis using 16S rRNA sequences showed that the presumptive causative bacterium was outside of but most closely related to family Brachyspiraceae. We propose 'Candidatus Maribrachyspira akoyae' gen. nov, sp nov., for this bacterium.