Genome analysis of the closest free-living bacteria of gutless marine worm endosymbionts

Osedax worms are whale-fall specialists that infiltrate whale bones with their root tissues, where they harbor endosymbiotic bacteria hypothesized to provide their hosts with nutrition by extracting organic compounds from the whale bones. Remarkably, little is currently known about physiological characteristics of endosymbionts and how they serve to uptake nutrition form whale bones. The worms’ endosymbionts were not observed in the spawned oocytes, which suggest that they are acquired from the free-living bacterial population in the environment. Recently, we had isolated the closest relatives to the endosymbionts of Osedax japonicus from sediment adjacent to the sperm whale carcasses. Two isolated strains, Amphritea japonica JAMM1866 and Neptunomonas japonica JAMM0745, belong to the family Oceanospirillance in the Gammaproteobacteria. Here, we thought that genomic studies of their free-living bacteria considerably accelerate the comprehensive understanding of physiological interaction between Osedax worms and its endosymbionts.
In this study, the complete genome sequences with A. japonica and N. japonica were elucidated using next generation technology, revealing genome sizes of approximately 3.8 Mb and 4.1 Mb, respectively. The metabolic pathway inferred from both genomes reveals the capability for growing heterotrophically with the waste compounds of worm metabolism such as acetate, lactate, malate, and succinate. Also, their genomes encode a bidirectional ammonium uniporter and a urease operon adjacent to urea ABC transporter for urea uptake. Ammonium and urea uptake by the worm symbionts would not only aid the host in the removal of these toxic waste products, but also lead for the symbionts to supply essential amino acid in host worms. Another interesting metabolic features are the presence of pathways for carbon storage compound polyhydroxyalkanoate biosynthesis. Given the ability of symbionts to recycle the nitrogen and conserve a resource of carbon and energy, it would be highly advantageous for the symbiosis. Genome analysis of the symbiotic bacteria is now underway and will allow us to further gain insight into Osedax worm symbiosis.

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First Name: 
Yoshihiro
Last Name: 
Takaki
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+81-46-867-9648
Affiliation: 
JAMSTEC
First Name: 
Masayuki
Last Name: 
Miyazaki
Affiliation: 
JAMSTEC
First Name: 
Morimi
Last Name: 
Teruya
Affiliation: 
OITC
First Name: 
Takao
Last Name: 
Yoshida
Affiliation: 
JAMSTEC
First Name: 
Noriyuki
Last Name: 
Sato
Affiliation: 
OIST
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Tadashi
Last Name: 
Maruyama
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JAMSTEC
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Trophic relations (including symbiosis)
Abstract ID: 
CBE5-180