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500 Million-Year-Old Symbiosis

Marine shallow water sandy bottoms on the surface appear desert-like and empty, but in the interstitial space between the sand grains, a diverse fauna flourishes. In addition to bacteria and protozoa, numerous animal phyla have been found here - some found only here. One of the strangest members of this interstitial fauna is Paracatenula, a several millimeters long, mouth- and gut-less flatworm, which is found in areas from tropical oceans to the Mediterranean. These worms are the focus of a research project led by Jörg Ott at the Department of Marine Biology of the Univ. of Vienna. The surprising results of this research have now been published in the Proceedings of the National Academy of Sciences (PNAS).

In the early 1970s, at the time of the discovery of Paracatenula, it was already a mystery how the worms acquire their food without a mouth and gut. The solution to this question came unexpectedly: At deep ocean hot vents, giant mouth-less tubeworms were found. These – like Paracatenula – live in symbiosis with intracellular bacteria that oxidize reduced sulfur compounds. The energy obtained in this chemical process is used by the symbiotes to fix inorganic carbon into biomass – just like plants do using sunlight. Because of the high productivity of the symbiotes, their hosts can derive all their nutrition from them.

Many animals of different phyla from several habitats have been found to live in such a symbiotic association. Compared to the great diversity of these hosts, the diversity of the microbial symbiotes was strictly limited to members of only two classes, the Gamma and Epsilon Proteobacteria.
 
 

Comments (2)

  1. See TWiM #9 - Live in NOLA - for more on this from Nicole Dubilier, who also works on the symbiosis between mouthless worms and bacteria.
  2. Make that TWiM #8!

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