Because they seem unusually abundant this summer (and in anticipation of an upcoming post), I thought I’d talk about fireflies today – fireflies and their role in scientific research.
There are over 2,000 species of fireflies, and they are named such due to the bioluminescence they produce to attract mates and deter predators. The bioluminescent reaction is clearly seen on a hot summer night, especially in tropical and temperate climates. Many people have fond memories of catching fireflies as children, gathering them in a jar with holes poked in the lid and enjoying the soft glow – a bioluminescent nightlight.
Firefly in jar (Sounds like the title of an ode)
So what is bioluminescence? Bioluminescence is the production of light by a living thing (bios = living, lumen = light). This type of luminescence is a natural example of chemiluminescence – energy released as light through a chemical reaction. It is seen in a variety of organisms including anglerfish, fungi and glowworm beetles (which are distinct from the firefly larvae that are also sometimes called glowworms).
While, as kids, we loved the blinking lights of the fireflies, few of us probably understood how the yellow-green glow was actually created. It is indeed a chemical reaction.
Fireflies produce two compounds that make their light show possible. One is called luciferin and the other is luciferase. Luciferin is a pigment that reacts with oxygen to create the light we see. Luciferase is a catalyst in this reaction meaning that it speeds up the reaction without being used up itself. Other components within the firefly including magnesium and ATP, an energy source, fuel the reaction.
The energy resulting from the chemical reaction is released as heatless green, yellow, or reddish light (wavelengths between 510 to 670 nanometers for the light spectrum enthusiasts out there).
It is this light that we see twinkling around us on hot summer nights. In fact, scientists think the fireflies can control the pattern and speed of “twinkling” by controlling how much oxygen (a component of the reaction) they have in their bodies.
So what does this have to with scientists and research? It turns out that the luciferase produced by fireflies can be a powerful research tool. Organisms can be made to glow by engineering them to express the luciferase gene. The plant below expresses luciferase, and when watered with a luciferin-containing mixture, it glows brightly.
Probably the most common use of luciferase in labs, and one that I found helpful in my own research, is as a reporter for what is happening within the DNA of a cell. The luciferase gene can be engineered into a cell so that it is expressed only when a specific promoter – a segment of DNA that drives gene expression – is active.
So, if I wanted to know if a chosen promoter was active, I would create a stretch of DNA in which my promoter in question would lead to creation of luciferase when active. Then, by adding luciferin to the mix, the presence or absence of light would tell me if luciferase was expressed and if my promoter was active.
Active promoter –> luciferase expression + luciferin = light (as in a firefly)
Inactive promoter –> no luciferase expression + luciferin = no light
Using this “equation” then, scientists can determine if a stretch of DNA is active merely my measuring whether light is produced. This is one way in which firefly luciferase helps scientists do their work.
So the next time you catch a firefly, thank it for its contribution to science. And then let it go so it can scare away predators, attract a mate and entertain kids of all ages with its bioluminescent backside.