Imagine standing on the deck of a ship out in the open ocean at night, in wonder at the twinkling stars. In the inky black water below you may also notice blinking, flashing lights, but it is not a reflection of the stars above. These bright displays are made by marine organisms via bioluminescence, a biological reaction that releases light. Researchers have found that as many as 3 out of every 4 species in the open ocean are capable of bioluminescence. It turns out that bioluminescence is a crucial communication tool for the majority of marine organisms, big or small.
Why do ocean creatures need to make their own light? As sunlight travels from the surface of the ocean into the depths, water molecules scatter and absorb the light. If you travel more than 200m (656ft) below the surface, the light becomes so scattered that it is nearly undetectable. With a maximum recorded depth of 11,000m or 36,000ft, the majority of the ocean exists in complete darkness. Animals in the so called midnight zone have developed large bulbous eyes to perceive even the tiniest glimmer. Light then is a precious resource, and creatures that make their own light can use it for communication. Luminescence can be used to defend against predators, find prey, or locate a mate–all essential functions that would be hindered without the use of bioluminescence.
To make bioluminescence, an organism much produce two molecules: a light-emitting pigment, luciferin, and an enzyme, luciferase. This interaction between the two molecules releases light, which usually appears blue or green. Many distinct groups of organisms use this process to create light, and now we can too.
In the human realm, bioluminescence can be used to treat cancer. Researchers are investigating a method called photodynamic therapy as an alternative to chemotherapy. The therapy uses a light-activated molecule called a photosensitizer to attack cancer cells. Activated photosensitizers release oxygen, starting a reaction that kills cancer cells and the surrounding vasculature, cutting the tumor off from nutrients. Unfortunately, light does not penetrate well through tissues so it can be difficult to deliver the necessary intensity using external sources, such as therapeutic lasers. In contrast bioluminescence is a molecular mechanism, which can be deployed locally to cells. A photosensitizer and luciferase can be attached to a cancer cell tagging molecule, which will then adhere to a cancer cell. Adding luciferin will then cause a light-emitting reaction with luciferase, which will activate the photosensitizer and kill the cancer cell.
Another treatment for cancer is resection, or surgically removing cancerous tissue. Bioluminescent tagging of cancer cells can be used to identify even small amounts of cancer cells while surgery is taking place. Mammalian tissue does not emit light so there is a large contrast between the tagged and untagged cells. A surgeon's goal is to remove as much cancerous material as possible, while leaving behind the healthy tissue. Because tumors can grow erratically into healthy tissue, there is not always a clear line where one stops and the other begins. Therefore methods like bioluminescent tagging are especially useful to distinguish between the two. Think of it as a way for the body to communicate with the surgeon: shining blue or green, cancer; no light, healthy tissue.
Bioluminescence is truly a natural wonder. While it may inspire awe from sheer beauty, it is also an important tool to understanding how species interact in the deep ocean. What's more is the light-emitting mechanism can be harnessed to enhance human medicine. Studying the ocean can be exciting and worthwhile on it's own, but the real impact comes from applying what we learn to benefit humankind.
About the Author
 Hailing from the deserts of Arizona, Mackenzie Carter is an enthusiastic masters student in the College of Veterinary Medicine. She is currently studying tissue engineering to model disease states in bone, namely panosteitis in canines. Mackenzie loves hands on projects, from ceramics to solar powered robots. In her free time she explores her passions: cephalopods, tea, and swing dancing. You can connect with Mackenzie via email at mackenziecarter@uga.edu. |
