Ever wondered what happens to the bones of dead whales that fall to the sea floor?
Well, they're feasted on by 'bone worms' of the Osedax genus. These worms are both mouthless and gutless, yet still manage to gain entry to the nutrients within the bones.
Now scientists at Scripps Institution of Oceanography at UC San Diego have discovered that these worms secrete a bone-melting acid to penetrate the bones.
"The acid presumably allows the worms to release and absorb collagen and lipids that are trapped in bone," said researcher Martín Tresguerres. "This model is remarkably similar to how mammals repair and remodel bone, however Osedax secrete acid to dissolve foreign bone and access nutrients."
In their report, the scientists describe a process in which the worms use a "proton pump" to secrete acid onto the bone (female worm pictured above by Greg Rouse).
Tresguerres says similar acid-secreting enzymes exist in all other organisms, such as in human kidneys to handle blood and urine functions.
Because they lack mouths, bone worms must use an alternative method of consuming nutrients from whale bones. Bacteria that live symbiotically within the worms are involved in this process, however, the exact mechanism is not yet fully understood. Some evidence suggests that the symbiotic bacteria metabolise bone-derived collagen into other diverse organic compounds, and that the worms subsequently digest the bacteria for their own nutrition.
A 2011 study led by Greg Rouse of Scripps found that bone worms are capable of making a living on other bones as well as those of whales, including fish. That finding supported a hypothesis that Osedax's bone-eating lifestyle may have evolved millions of years ago, even before the dawn of marine mammals.
To continue learning more about bone worms, the scientists plan to collaborate with colleagues at the Monterey Bay Aquarium Research Institute in the coming months to collect and study additional bone samples with live worm specimens. They also plan to maintain live Osedax in aquaria at Scripps to study their physiology.
"Determining how Osedax gets into bones was the first challenge in understanding the nutrition of these bizarre animals," said Rouse. "Now we'd like to understand how they transport and utilise the nutrients that they have uncovered."
The results of the study were published in the May 1 online edition of the Proceedings of the Royal Society B (Biological Sciences).
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