When whales die, they fall to the floor of the sea. As described in the above video from the Monterey Bay Aquarium Research Institute, these “whalefalls” provide a huge influx of food to a wide variety of animals and microbes. Not only is the flesh devoured, but the bones are consumed as well, by the aptly named “boneworms.” Many species of boneworms (Osedax worms) help make the entire whale skeleton disappear in less than a decade. These worms burrow the ends of their bodies into the bone and, with the help of endosymbiotic bacteria, turn the bone into food. But how do they manage to burrow into whale bone? Here, scientists from the Scripps Institute of Oceanography found that the worms are able to produce and secrete high concentrations of acid that can literally dissolve bone. It turns out that this is similar to how cells in your own body dissolve bone, including when the roots of baby teeth are dissolved before falling out. Aren’t you glad Osedax worms are only found in the ocean?
How to get into bones: proton pump and carbonic anhydrase in Osedax boneworms.
“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 CO2 into H(+) and HCO3(-), 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 CO2 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.”