Affiliation:
1. Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 93092-0202, USA
Abstract
Osedax
are gutless siboglinid worms that thrive on vertebrate bones lying on the ocean floor, mainly those of whales. The posterior body of female
Osedax
penetrates into the bone forming extensions known as ‘roots’, which host heterotrophic symbiotic bacteria in bacteriocytes beneath the epidermis. The
Osedax
root epithelium presumably absorbs bone collagen and/or lipids, which are metabolized by the symbiotic bacteria that in turn serve for
Osedax
's nutrition. Here, we show that
Osedax
roots express extremely high amounts of vacuolar-H
+
-ATPase (VHA), which is located in the apical membrane and in cytoplasmic vesicles of root and ovisac epithelial cells. The enzyme carbonic anhydrase (CA), which catalyses the hydration of CO
2
into H
+
and HCO
3
−
, is also expressed in roots and throughout
Osedax
body. These results suggest
Osedax
roots have massive acid-secreting capacity
via
VHA, fuelled by H
+
derived from the CA-catalysed hydration of CO
2
produced by aerobic metabolism. We propose the secreted acid dissolves the bone carbonate matrix to then allow the absorption of bone-derived nutrients across the skin. In an exciting example of convergent evolution, this model for acid secretion is remarkably similar to mammalian osteoclast cells. However, while osteoclasts dissolve bone for repairing and remodelling, the
Osedax
root epithelium secretes acid to dissolve foreign bone to access nutrients.
Subject
General Agricultural and Biological Sciences,General Environmental Science,General Immunology and Microbiology,General Biochemistry, Genetics and Molecular Biology,General Medicine
Cited by
48 articles.
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