Although it was known previously that many sea creatures glow — a phenomenon known as bioluminescence — the benefits of this biological light production have been unclear — until now. Many marine creatures glow deep below the ocean surface. Bioluminescence is observed even in some marine bacteria, which emit a steady light once they have attained a certain level of concentration of organic particles, a state known as quorum sensing. Now, researchers at the Hebrew University of Jerusalem have discovered that light emitted by the bacteria attracts predators, generally zooplankton, which ingest the bacteria but are unable to digest them. The luminescent bacteria continue to grow inside the zooplankton, which also glow and are then attacked by their own predators — fish — which can easily spot the zooplankton in the dark. Glowing bacteria in petri dishes. (Image: Hebrew University of Jerusalem) In experiments conducted in total darkness, researchers found that nocturnal fish easily ingested glowing plankton, while the fish were not attracted to the zooplankton that had swallowed bacteria that did not glow as a result of having undergone genetic mutations. Further investigation revealed that the luminous bacteria survived even the passage through the fish. Once the marine bacteria reached the digestive system, they had achieved their goal, since the digestive tract is full of nutrients and provides a means of transport into the wide ocean, said professor Amatzia Genin, head of the department of evolution, systematics and ecology at the university. The phenomenon of quorum sensing, which regulates bacterial bioluminescence, explains that zooplankton “know” that a light in the water indicates the presence of a rich source of organic material on which bacteria grow. “In the dark, deep ocean the quantity of food is very limited; therefore it is worthwhile for the zooplankton to take the risk of becoming glowing themselves when contacting and consuming the particle with glowing bacteria, since the profit of finding rare food there is greater than the danger of exposing themselves to the relatively rare presence of predatory fish,” Genin said. For more information, visit: www.huji.ac.il/huji/eng/