The often spectacular luminescent displays of marine organisms have always triggered our curiosity. Now, these ecological wonders are providing a wealth of medical and research applications.

Bioluminescence, the production of visible light by living organisms, is a "magical" phenomenon that appears as striking displays at dusk or at night. One of the most iconic luminescent organisms is the firefly, yet light production is observed in many habitats and is most prevalent in the marine environment. Bioluminescence occurs in a great diversity of species from every living Kingdom, except Plants; it serves as a form of visual communication and is therefore produced with optical characteristics (wavelength, intensity, kinetics) for the produced light to be optimally seen by the observer. To the producer, bioluminescence functions are diverse and include illumination and attraction of prey, attraction of conspecifics for mating, camouflage, and predator avoidance or repulsion.

The light originates from a biologically controlled chemical reaction (chemiluminescence). In this reaction, an enzyme (luciferase) catalyzes the oxidation of a substrate (luciferin). Luciferases are oxygenases with no homology to any other proteins, while luciferins are produced in vivo or obtained through the diet. There are several systems of luciferin-luciferase reactions that are chemically unrelated, the only common characteristic being that molecular oxygen is always needed for light production. In some cases luciferin, luciferase, and oxygen precombine to form a stable intermediate called a photoprotein, in which light production is triggered by a specific ionic cofactor such as Ca²⁺. Today, although dozens of bioluminescent systems may exist, only a handful are well described chemically, thus creating opportunities for new discoveries.

There is high demand in bioengineering for molecules capable of receiving energy, either radiometric or electrochemical, and transform it into light, or for organisms capable of producing light under specific conditions. Our laboratory research interests focus on bioluminescence organisms keeping this framework in mind, considering the specific factors underlying the light production in organisms for application in various fields.

Luminescent Dinoflagellates to Visualize Hydrodynamic Flows

Dinoflagellates are eukaryotic cells that are the most abundant sources of luminescent displays in coastal waters; their light flashes are stimulated by handling by a predator with the aim to distract its feeding, or to serve as a "burglar alarm" by lighting up the predator so that it itself becomes more visible to its own predators.

However, any flow condition that provides sufficient mechanical stresses will also trigger light emission. Flow stimulation is associated with the movement of ships and swimming animals, as well as breaking waves, creating spectacular displays of bioluminescence during periods of high dinoflagellate abundance. "Calibrating" the relationship between flow stresses and light emission has allowed dinoflagellate bioluminescence to be applied as a flow visualization tool for both oceanographic and engineering approaches. Examples include visualization of the boundary layer of a swimming dolphin, and quantifying flow stresses in bioreactors (fig. 1) and within breaking wave crests (fig. 2). Recent advances in modeling the flow stimulation of bioluminescence continue to promote the use of dinoflagellate bioluminescence as a reporter of flow stresses.

Bioluminescence to Assess Environmental Quality

The bioluminescence of bacteria is used in bioassays of environmental quality, in which reductions in light intensity serve as an index of sub-lethal toxicity. Similarly, a bioluminescence assay using dinoflagellates serves as a proxy for eukaryotic cells. While sensitive, these assays rely on assessments made with unicellular organisms.

Recently we developed a bioluminescence bioassay using brittlestars (fig. 3), a "cousin" of starfish in which about half of the species produce light. The light is likely used to deter predators, especially when associated with autotomy, in which an attacking predator is lured away by a glowing arm that has been "voluntarily" released. Light production is under nervous system control and exhibits characteristic patterns of intensity and kinetics when triggered in the laboratory using neuro-mediators. We have used changes in these patterns, which indicate malfunction of the neurological control of light production in the brittlestar, as a proxy for assessing environmental quality. Thus the brittlestar assay complements commercialized assays using luminescent unicellular organisms by integrating another level of biological complexity. As brittlestars live in association with sediment, where contaminants may accumulate, they are therefore in the first line of exposure for contaminants leading to possible toxicity. Because the nervous system is one of the most vulnerable tissues, changes in light production patterns are interpreted as indicative of sub-lethal toxicity and neuronal impairment. By performing transplants of brittlestars in cages into different environments, and following their light production patterns as well as contaminants uptake over time, we are able to assess quality of an environment.