A study describes the symbiosis between a flatworm and its bacterial partner in which the bacteria store energy and secrete nutrition for the flatworm, which does not digest the bacteria. Symbiotic relationships between bacteria and animals are common, and in cases where bacteria serve to store chemical energy for the host, the host typically digests the bacteria to access the energy. Harald Gruber-Vodicka and colleagues studied a marine Paracatenula flatworm from Elba, Italy and its intracellular endosymbiotic bacteria, Candidatus Riegeria santandreae. The authors found that the genome of the bacteria was significantly reduced in size compared with nonsymbiotic relatives, a process that likely occurred over a 500-million-year period of symbiosis between the two species. The remaining genes in the bacteria were highly specialized for efficient production and storage of carbon and energy, to a degree not previously observed in symbionts with similar genome sizes. Further, rather than being digested, the bacteria secrete outer membrane vesicles to supply nutrition to Paracatenula . According to the authors, the results cast the bacteria in a previously unrecognized role as the primary unit of chemical energy storage in a symbiotic relationship.
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Article #18-18995: "Chemosynthetic symbiont with a drastically reduced genome serves as primary energy storage in the marine flatworm Paracatenula ," by Oliver Jäckle et al.
MEDIA CONTACT: Harald Gruber-Vodicka, Max Planck Institute for Marine Microbiology, Bremen, GERMANY; tel: 004915157884139; e-mail: < hgruber@mpi-bremen.de >
Proceedings of the National Academy of Sciences