If something smells bad, it's a good rule of thumb that it's toxic too. For most creatures a dose of hydrogen sulphide is enough to kill them, but not vestimentiferan tubeworms that live around hydrothermal vents deep on the ocean floor. They have made a pact with symbiotic bacteria that protect them from the harmful effects of sulphides. The bacteria fuel their metabolism with hydrogen sulphide supplied through the worm's blood. In return the bacteria supply the worms with sugars and ammonia for nourishment. But having turned one of the planet's most toxic environments to its own advantage, the worm runs the risk of being poisoned from the inside by its partner's waste:protons. James Childress and his student Peter Girguis were fascinated by how the worm solves its lodger's waste disposal problem, until they measured the rate that the worm excretes protons into the environment. They discovered that the worm...

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