Bioluminescence — the ability of an organism to produce and emit light — is nature's light show. Plants, insects, fish, and bacteria do it, and scientists understand how. Until now, though, we didn't know how fungi glow.
Now, thanks to research led by Zinaida Kaskova in the Institute of Bioorganic Chemistry at Russian Academy of Sciences, we've figured out how some mushrooms glow. The researchers published their work in the journal Science Advances.
Most often, light emitted from an organism results from the reaction between a chemical called luciferin and an enzyme called luciferase in the presence of oxygen, which produces a chemical, oxyluciferin. Usually, reaction emits light at one wavelength, so we see it as one color.
Organisms use this process to serve many functions, most often to provide a signal, communicate with other organisms, lure prey, or to illuminate their surroundings.
Tourists visit Puerto Rico's Vieques Island to witness firsthand the magic of bioluminescence that is abundant in the ocean there. And in 2005, a space satellite picked up images of "milky seas" — an example of unusually strong bioluminescence produced by colonies of bacteria in a microalgae bloom in the surface waters. The remarkable vision lit up an area in the Indian Ocean the size of the state of Connecticut.
Fireflies, perhaps the most well known of all bioluminescent organisms, have provided scientists with a source of luciferase for experiments and countless hours of viewing pleasure to children and adults alike.
But scientists first discovered and extracted green fluorescent protein from a jellyfish called Aequorea living in Puget Sound. This creature not only glows, but it also has a green fluorescent protein which glows under certain light conditions (blue and ultraviolet, specifically). Osamu Shimamura, Martin Chalfie, and Roger Tsien shared a Nobel Prize for their work with this protein.
Scientists have synthesized green fluorescent protein and use it as a marker in many research labs. They insert the gene that makes the fluorescent protein into a cell, making it glow green so it can be easily located and identified in a dish. Scientists have found several other colors of fluorescent proteins, as well, which they often used in tandem.
There is also bioluminescent imaging, a technique that uses luciferase — inserted into the animal's or a cell's genes — to visualize tumors and other structures, once luciferin is added to trigger the light-generating reaction. Scientists commonly use luciferase to detect if they've successfully inserted a genetic sequence into a cell. The genetic sequence contains both the bioluminescent gene and the gene of interest, so if it glows, you know the cell contains both.
And let's not forget about science for consumerism. The "GloFish" is a zebrafish where different colored fluorescent proteins have been inserted into their cells to create fish that glow in many fluorescent colors. It's the only genetically modified animal available in the US for public sale in pet stores.
One last bastion of glowy goodness is still not well understood: the glow mechanisms of mushrooms. Over 80 different species of fungi are known to emit light via bioluminescence, but until the research by Kaskova and her team, we didn't know how it worked.
By studying extracts of a fluorescent mushroom native to Brazil, called Neonothopanus gardneri, as well as Neonothopanus nambi, a fluorescent, but poisonous mushroom found in the rainforests of southern Vietnam, Kaskova and her team found the components involved in the production of bioluminescence by mushrooms.
Scientists had already found a chemical in the mushrooms called hispidin that combines with oxygen to form 3-hydroxyhispidin, which acts as the fungal equivalent of luciferin. And adding oxygen to this protein created bioluminescence, but they hadn't yet identified the fungal equivalent of oxyluciferin — the product of this reaction, which does the actual glowing in other organisms.
In the new study, Kaskova and her colleagues reacted the 3-hydroxyhispidin with oxygen and analyzed the product with a sophisticated machine called an HPLC-photodiode array electrospray ionization mass spectrometer. This analysis provided the scientists with the composition of the glowing reaction product, which they then synthesized in the lab.
They found that once the glowing protein emits its light, it degrades to caffeic acid and that can be recycled to make more 3-hydroxyhispidin — so the bioluminescence can continue.
Kaskova and her team believe that the fungus's 3-hydroxyhispidin may be able to interact with different types of glow-creating proteins — leading to a range of color emissions and intensities — a unique and beautiful feature of mushroom bioluminescence.
Unraveling the mechanism behind this remarkable aspect of nature has allowed humans to both enjoy and exploit the process for our use. The more we delve into these natural visions of beauty, the more we can find uses for them in our lives — or just heighten our appreciation for their light shows.
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