Deep-sea Sea Pigs Harbor Unusual Bacteria

WHO:

Phys.org - Researchers at the University of Tokyo discovered a bacterium living beneath the “skin” of deep-sea sea pigs.

EurekAlert! - Yu Yoshida, a Ph.D. student at the University of Tokyo’s Graduate School of Frontier Sciences, is a lead author of the study.

EurekAlert! - The multi-institutional Japanese research team included University of Tokyo researchers.

EurekAlert! - The bacterium is named *Candidatus Abyssoplasma scotoplanesicola* and is proposed as a new genus and species.

EurekAlert! - The paper’s authors are Yu Yoshida, Yosuke Nishimura, Hajime Itoh, Masumi Hasegawa-Takano, Tsuyoshi Takano, Naohisa Wada, Kento Tominaga, Akito Ogawa, Wataru Iwasaki, Yasuhiro Gotoh, Takehiko Itoh, Tetsuya Hayashi, and Susumu Yoshizawa.

WHAT:

Phys.org - DNA analysis found the bacterium has a minimized genome of 649,000 bases.

EurekAlert! - In body-wall samples from three sea-pig species, the bacterium accounted for more than 70% of bacterial 16S rRNA gene sequences.

EurekAlert! - Genes for surface-associated protein groups accounted for 27.6% of the bacterium’s genome; some encode proteins longer than 5,000 amino acids. Bacterial proteins average about 300 amino acids.

EurekAlert! - The bacterium’s genome is about one-seventh the size of the *E. coli* genome; researchers did not detect genes for some commonly found energy-generating pathways.

EurekAlert! - Sea pigs are sea cucumbers that recycle organic matter and nutrients; their bodies can shelter young king crabs. In some deep-sea areas, sea cucumbers make up more than 90% of the biomass of large bottom-dwelling animals.

EurekAlert! - The study, “Genomic, spatial, and evolutionary insights into a dominant Mycoplasmatota symbiont colonizing the body wall of deep-sea holothurians,” appeared in *ISME Host Microbe*.

EurekAlert! - The authors declared no conflicts of interest.

WHERE:

EurekAlert! - Researchers extracted DNA from tissues of eight sea pigs collected during deep-sea expeditions and used fluorescent imaging to locate bacteria in host tissue.

WHY:

EurekAlert! - The study aims to clarify the characteristics and location of bacteria living in sea-pig body walls and identify functions retained by bacteria living closely with hosts.

EurekAlert! - The bacterium is thought to rely on host tissues for amino acids, nucleic acid precursors, lipids, and mineral nutrients; what sea pigs gain from the relationship is unknown.

HOW:

Phys.org - Researchers used fluorescent imaging to determine where the bacterium lives beneath the sea pig’s skin.

EurekAlert! - The team compared DNA from different tissues, identified abundant bacteria, reconstructed dominant bacterial genomes, and used fluorescence imaging to pinpoint their locations.

EurekAlert! - The giant surface proteins may be involved in interactions with host tissues or bacterial clustering; a possible protective role against pathogens has not been confirmed.

(UPDATED November 13, 2026 02:04 UTC)

Tokyo researchers discovered a bacterium living beneath the skin of deep-sea sea pigs. It dominated bacterial samples across three species, with an unusually reduced genome. The bacterium may draw nutrients from its hosts, but benefits to sea pigs remain unknown.