There dwells in the foul mud of a remote lagoon in the Philippines a four feet long dark slithering creature. This giant shipworm with pinkish siphons at one end and an eyeless head at the other was discovered by Daniel Distel, a professor at Northeastern University and his colleagues. They say studying the animal could add to our understanding of how bacteria causes infections and, in turn, how we might adapt to tolerate—and even benefit from them.
“Most shipworms are very delicate, translucent, usually white, beige or pink,” says Distel, “They’re mostly small, a few centimeters long. You have to be very careful not to damage them when you’re taking them out of the wood, where they live. This thing was like a baseball bat. It was a beefy, muscular animal, jet black.” This rare shipworm was the focus of a two-decade-long search before it was finally discovered.
In a newspaper published in the Proceedings of the National Academy of Sciences, Distel and his colleagues present their research on the lives of shipworms. They describe how it does not eat, at least not much, due to its tiny digestive system—but instead, bacteria living inside its gills convert sulfur gas from rotting wood into nutrients to keep it alive.
Usually, shipworms eat wood, and hence their name “termites of the sea.”Bacteria in their gills secrete enzymes that travel to their gut and break down the wood—which are made of cellulose, an organic material—turning it into sugar. Wood can also serve as a source of hydrogen sulfide—sulfur gas that smells like rotten eggs. “We believe that somewhere along the line a shipworm acquired a sulfur- oxidising bacteria as a symbiont, and it was able to get energy not just from the wood but also from the inorganic gas hydrogen sulfide coming from the wood as it rotted,” says Distel. “Eventually the new symbiosis completely replaced the old symbiosis.”
“These bacteria live inside the animals’ cells, alongside the cytoplasm,” says Distel. “If we or any vertebrate had bacteria living inside our cells, we’d be very sick. In the long run, studying these symbioses may tell us a lot about the process of disease. What is it about these bacteria that they can infect the host yet not harm it? How does the host learn to tolerate, and even benefit from, the bacteria?”
Anisha Naidu
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