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On the second Tuesday of every month at 7:45 a.m. and 5:45 p.m., we hear from our contributors in the field. Susan Knight and Gretchen Gerrish both work for the University of Wisconsin-Madison’s Center for Limnology at Trout Lake Station. Scott Bowe is the Director of Kemp Natural Resources Station.

Pay Attention to the Things That Glow in the Night

Wikimedia Commons
The saprobe Panellus Stipticus displaying bioluminescence.

It’s the second Tuesday of the month, which is when we check in with our commentators in the field.

In this month’s episode of Field Notes, Susan Knight of Trout Lake Station suggests we take a walk in the dark to see fireflies and other glowing organisms.

It is almost firefly season. I am sure I am not the only one who is transported back to kid-hood when I see the first fireflies of the summer. Fireflies are beetles who make conspicuous use of bioluminescence, the emission of light by living organisms. Fireflies are not the only bioluminescent creatures; many other animals, especially in the ocean, use bioluminescence to signal their presence in the dark.  However, there are also bioluminescent mushrooms, and even bioluminescent bacteria.  And there may even be bioluminescent trees in our future.

Sometimes knowing how something works, especially something as magical as a firefly’s light, can take away some of the fun. However, knowing how bioluminescence works really just adds to the coolness.  A nineteenth century pharmacologist was the first to work out the process that makes organisms glow, and named the chemical and its sister enzyme, luciferin and luciferase. The reaction needs energy from the cell as well as oxygen and often another chemical such as magnesium.

Why did the pharmacologist name the chemicals after Lucifer? Through history, the name Lucifer referred to the Devil, but it also referred to the planet Venus, when appearing as the morning star. But the Latin meaning of lucifer, uncapitalized, and as an adjective, means “light bringing”. So, these chemicals are indeed aptly named. However, while the chemicals causing the glow are known as luciferin and luciferase, different organisms have their own special flavor of these chemicals, and there is evidence that bioluminescence has evolved independently at least 40 times.

Besides fireflies, some mushrooms also glow, and this is known as foxfire. Aristotle, back about 300BC, mentioned damp, glowing wood but, unlike fire, it was cold to the touch. Throughout the world, there are more than 75 species of bioluminescent fungi, and, for you mushroom buffs, almost all of them are Basidiomycetes. According to our Northwoods mushroom maven, Ann Small, honey mushrooms and bitter oysters are two of our local growing – and glowing - fungi. The fungi emit a greenish light, and it glows non-stop, though you are only likely to notice it if you take a walk in the dark. Bitter oyster (or Panellus stypticus), is found in many parts of the world, including Japan, New Zealand, Russia and Europe, but only those specimens in eastern North America are bioluminescent. It is commonly found on a variety of rotting hardwoods. The glow emanates from the edges of the gills of this fan-shaped mushroom. Why should a mushroom glow?  Back in the 1920s, a scientist learned that the glow is most intense when the spores are close to maturity, leading to the speculation that the glowing fungi attract insects so that they might spread the spores.

The honey mushroom, or Armillaria mellea also glows. Unlike the bitter oyster, where the fruiting part of the mushroom glows, it is the root-like collection of hyphae or mycelium that glows when the filaments infect and start killing a tree, often an oak. These are not always visible, and so why should these fungal threads glow?  In this case, the glowing threads are likely discouraging animals from eating it. 

One of the eeriest examples of bioluminescence is a glowing bacterium, Photorhabdus luminescens, living in the gut of tiny roundworms called nematodes. Like Bonnie and Clyde, the glowing bacterium and its nematode partner together become a killing machine. The nematode, common in soil, finds and attacks an insect, and injects the bacteria into the insect. The glowing bacterium liquifies the insect so that its oozy innards can be absorbed. Why does it glow? The bacterial glow might serve to lure unsuspecting insects to the predatory nematodes. Though this Aliens-like story is creepy, it gets even creepier.  Wounded Civil War soldiers, often languishing on the ground, were sometimes found to have glowing wounds.  People have speculated that the glow was due to infection by this bacteria and nematode duo. Amazingly, these wounded soldiers were not hurt by these glowing bacteria because the bacteria themselves apparently produce an antibiotic that possibly helped them heal.

And now back to the trees.  Scientists working at MIT have figured out how to package luciferin and luciferase, the partner chemicals responsible for bioluminescence, into nanoparticles and inject them into plants. The chemicals tap into the energy of the plant cells and cause the plant to glow. So far, they have only managed to incorporate the luciferin-loaded nanoparticles into water cress. But, with some tweaking, they believe they could create glowing trees to provide soft, dim light that might even replace street lights one day.

We’ll probably all be happier not seeing any of the glowing bacteria teamed up with their nematode co-conspirators. But, I encourage you to get out in the dark, and enjoy the fireflies. Maybe you’ll even see some foxfire.  You can keep your eyes open for glowing oak trees, but I wouldn’t hold my breath.

Susan Knight works for the University of Wisconsin-Madison’s Center for Limnology at Trout Lake Station and collaborates closely with the Wisconsin Department of Natural Resources. She is involved in many aspects of aquatic plants, including aquatic plant identification workshops and research on aquatic invasive plants. She is especially fond of bladderworts.
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