Glowing, gutsy hitchhikers

To hungry humans, glow-in-the-dark food may seem suspicious and unappetizing. To creatures that swim, slither and crawl in the darkest depths of the ocean, however, a glowing bug may be a welcome and easy snack.

Scientists have come up with many ideas about why organisms light up. New experiments on tiny, glow-in-the-dark bacteria that live in the sea support the idea that a microbe’s glow isn’t just for show. Hungry animals are attracted to the light and eat the microbes, which then cruise around the ocean inside the animal’s guts. The idea is more than 30 years old, but new research from scientists in Israel and Germany boosts confidence in the theory.

“It’s terrific to see this experiment,” J. Woodland Hastings told Science News. Hastings, a biologist at Harvard University who specializes in studying critters that glow, was not involved in the study. “It’s nice to see these ideas confirmed.”

Lots of animals, from squid to fish, light up in the deep ocean. Inside their bodies, chemical reactions cause the glow, which is called bioluminescence.

To test the idea that the light helps bacteria attract the attention of animals and hitch a ride, Margarita Zarubin studied bacteria from 2,000 feet beneath the surface of the Red Sea. Zarubin, who is now finishing her doctorate at the Interuniversity Institute for Marine Sciences in Eilat, Israel, conducted the experiments while a student at the University of Germany in Oldenburg.

She began by placing brine shrimp in a tank with two kinds of deep-sea bacteria. One type glowed, the other didn’t. Hungry shrimp devoured the lighted bugs, but left the others alone. After eating the glowing bacteria, the shrimp also lit up — the bacteria glowed through the animals’ bodies.

“We could see the luminescence from inside their guts,” Zarubin told Science News.

Next, Zarubin and her colleagues took a step up the food chain. The team offered hungry fish glowing shrimp and nonglowing shrimp. Fish gobbled only the glowing shrimp; the other shrimp swam by in safety.

Finally, Zarubin and her team studied poop from the fish. The scientists found the bacteria alive and well, which meant they had survived the journey through shrimp and fish guts. Zarubin told Science News that this unusual mode of transport, hitching rides in intestines, spreads bacteria faster than natural movements of the ocean will.

Marine biologist Michael Latz of the Scripps Institution of Oceanography in La Jolla, Calif., told Science News that studying the gutsy journey of these bacteria may also help researchers understand how other germs spread through the sea.

POWER WORDS (adapted from the New Oxford American Dictionary)

bioluminescence The emission of light by living organisms such as fireflies and deep-sea fishes.

marine From or of the sea.

bacteria Members of a large group of single-celled microorganisms, including some that can cause disease.

food chain A series of organisms where each depends on the next as a source of food.