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Abstract

The digestive organs of terrestrial isopods harbor bacteria of the recently proposedmollicute family Hepatoplasmataceae. The only complete genome available for Hepatoplasmataceae is that of “Candidatus Hepatoplasma crinochetorum”. The scarcity of genome sequences has hampered our understanding of the symbiotic relationship between isopods and mollicutes. Here, we present four complete metagenome-assembled genomes (MAGs) of uncultured Hepatoplasmataceae members identified from shotgun sequencing data of isopods. We propose three novel species “Candidatus Tyloplasma littoralis” identified from the semiterrestrial isopod Tylos granuliferus, “Candidatus Hepatoplasma vulgare” identified from the common pill bug Armadillidium vulgare, and “Candidatus Hepatoplasma scaber” identified from the common rough woodlouse Porcellio scaber. Phylogenetic analysis of 16S ribosomal RNA sequences showed that “Candidatus Tyloplasma littoralis” and other semiterrestrial isopod-associated mollicutes form a sister clade to terrestrial Hepatoplasma members, justifying their assignment to a novel genus. Phylogenomic analysis of 151 mollicutes confirmed that Hepatoplasmataceae is a sister clade of Metamycoplasmataceae in the order Mycoplasmoidales. Our analysis also revealed that that Hepatoplasmataceae lack major metabolic pathways but has a likely intact type IIA CRISPR-Cas9 machinery, indicating that these mollicutes have an ectosymbiotic lifestyle with high nutritional dependence on their host. We did not find any evidence that Hepatoplasmataceae encode digestive enzymes that could provide nutritional benefits to the host, which suggests that they may act as defensive symbionts.

Funding
This study was supported by the:
  • Japan Science and Technology Corporation (Award JPMJSA1806)
    • Principle Award Recipient: Ikuo Hirono
  • Japan Society for the Promotion of Science (Award JP15H02462)
    • Principle Award Recipient: Ikuo Hirono
  • Japan Society for the Promotion of Science (Award JP19H00949)
    • Principle Award Recipient: Ikuo Hirono
  • Japan Society for the Promotion of Science (Award 19J21518)
    • Principle Award Recipient: Satoshi Kawato
  • This is an open-access article distributed under the terms of the Creative Commons Attribution License.
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/content/journal/acmi/10.1099/acmi.0.000592.v1
2023-03-07
2024-06-24
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http://instance.metastore.ingenta.com/content/journal/acmi/10.1099/acmi.0.000592.v1
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