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 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 from tropical oceans to the Mediterranean. These worms are the focus of a research project led by Jrg Ott at the Department of Marine Biology of the University of Vienna with funding from the Austrian Science Foundation (FWF). The surprising results of this research have now been published in the journal 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 symbionts to fix inorganic carbon into biomass just like plants do using sunlight. Due to the high productivity of the symbionts, 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 symbionts was strictly limited to members of only two classes, the Gamma and Epsilon Proteobacteria.
Paracatenula has Alpha-Proteobacterial "Riegeria" symbionts
One of the biggest surprises in the current study was that the symbionts of Paracatenula are indeed sulfur-oxidizing bacteria, but they are Alpha-Proteobacteria. Severa
|Contact: Harald Gruber-Vodicka|
University of Vienna