How research into glowing fungi could lead to trees lighting our streets

How research into bioluminescent fungi could lead to trees replacing street lighting

On a moonless night deep in a Brazilian rainforest the only thing you are likely to see are the tiny smears of illuminate from flitting fireflies or the ghostly glow of mushrooms scattered around the forest floor. Both consequences are the result of bioluminescence, the peculiar ability of some organisms to behave like living night-lights.

Bioluminescence has been invented dozens of hours in evolutionary history and serves a variety of purposes, from attracting mates and seducing prey to warding off predators. Its existence in fungi a rare if not unique occurrence of bioluminescence outside the animal and microbial worlds has posed more of a mystery. But scientists may now be able to explain not only why certain mushrooms glow in the dark, but how and in doing so they could be nearer to making glowing trees as a novel sort of street lighting.

Aristotle in 382 BC and the Roman scholar Pliny the Elder writing three centuries later both find the effect of fungal bioluminescence when they described the glowing illumination of the cold flame of damp wood. The ghostly glow afterwards became known as foxfire, probably from the Old French word fois meaning false, and the phenomenon appeared in many runs of literature, including The Adventures of Huckleberry Finn when Tom Sawyer used it to light up a tunnel.

Naturalists in the early 19 th century identified fungal growth as the source of the glow from wooden supporting rays used to shore up ours. Many fungis and mushrooms are now known to glow in the dark, and explanations for why they do it scope from it being a useless by-product of metabolism to a sophisticated anti-predator adaptation.

But the best justification seems to be that the night-light attracts insects and other animals to the fruiting bodies of fungi, who then spread the spores far and wide. Cassius Stevani at the So Paulo University in Brazil and colleagues showed this by scattering plastic mushrooms on the forest floor fitted with green LED illuminates that matched the eerie bioluminescence of Neonothopanus gardneri , a splendid mushroom that grows at the base of palm trees. He found the sunlight attracted the sort of bugs and other beasts that would be good at spreading spores. They also indicated the bioluminescence merely occurred at night ruling out the useless by-product hypothesi. Results indicate that the bioluminescence can attract animals to scatter spores. This additional dispersal mechanism might bestow to this fungus some advantage, especially in dense forest, Stevani says.

The exact technique of how mushrooms can generate a spooky glow remained a mystery, in contrast to the elucidation of the light-emitting pigments used by the many other forms of life that they are able produce bioluminescence.

But now a team led by Ilia Yampolsky of the Institute of Bio-organic Chemistry in Moscow has finally taunted apart the chemical structure of the fungal protein used to generate the ghostly incandescence of foxfire. They did it by the counterintuitive approach of looking for it in mushrooms that did not glow in the dark because it was here they guessed the precursors of the bioluminescence substance, known as luciferin, might be more easily procured and they were right.

The mechanism of fungal bioluminescence indicates the formation of luciferin from a certain precursor, Yampolsky says. It was established that the luciferin precursor is also present in non-luminous forest fungi, and more importantly it is about 100 times more abundant than in the biomass of luminous species. Hence, it built sense to extract the precursor from non-luminous fungi.

The term luciferin was first identified in the late 19 th century by French chemist Raphal Dubois, working on click beetles and bivalve molluscs. He gave the name luciferin to the substance that can be oxidised in air, with the help of the enzyme luciferase, to emit a greenish-bluish light.

But Yampolsky and his colleagues found that the bioluminescent fungi use a type of luciferin quite different from the eight other classes of molecule already chemically described in the animal and microbial worlds. He and his squad effectively detected the ninth luciferin, and the first to be found in the fungal-plant realm of life.

Fungal luciferin is chemically unrelated to other known luciferins, therefore it represents a totally different mechanism of light emission. “Its important” from the points of view of photochemistry, biochemistry and evolution. Furthermore, it dedicates the possibility to search for an unknown fungal luciferase, Yampolsky tells. Unlike the other luciferins, fungal luciferin is compatible with plant biochemistry, and I hope that this will eventually allow the creation of an autonomously luminescent plant, one that would not require the external addition of luciferin, but would be able to biosynthesise it by itself, he says.

This would be a key breakthrough in, for instance, designing a genetically modified tree that could glow in the dark and act as a sustainable source of street lighting. The notion is not as crazy as it may seem. The Glowing Plant Project, the first crowdfunding campaign for a synthetic biology application, is supported by the Harvard geneticist George Church, who once used to say even a weakly glowing bloom would be a great icon.

Animals that glow in the dark

The
The deep sea anglerfish deploys bioluminescent bacteria in the tip-off of a long appendage. Photograph: Alamy Stock Photo

Deep-sea anglerfish
In the abyssal darkness of the deep oceans no one can hear you screaming, especially if you are tricked by an angler fish ( Bufoceratias wedli ). The anglerfish cleverly deploys bioluminescent bacteria in the tip of a long appendage that hovers invitingly over its open mouth. This is a good example of bioluminescent mimicry, when something is not all that it appears in nature.

Dinoflagellates
These tiny marine plankton float on the ocean surface and offer one of the most spectacular displays of mass bioluminescence in nature when vast areas of ocean light up at night. Laboratory experiments show that the phenomenon can startle predators, interrupting their feeding behaviour and devoting dinoflagellates a transgres. One theory is that this phenomenon acts as a burglar alarm, attracting bigger predators to feed on the predators of dinoflagellates.

Fireflies
Fireflies are perhaps the best and most easily recognisable example of bioluminescence in nature. The insect controls the light it emits from its light organ by adding oxygen to a mix of other chemicals involved in the light-emitting reaction, including luciferin and the bioluminescent enzyme luciferase. As larvae, the light acts as a warning to predators that they dont savor very nice, and as adults the light is used to identify members of the same species and to attract the opposite sex.

Fishermen
Fishermen trawl a net containing glowing firefly squid off the coast of Namerikawa city in Japan. Photograph: AFP/ Getty Images

Firefly squid
Some species of squid utilize bioluminescent bacteria to provide counter-illumination to the underside of their bodies, so they are more camouflaged against the light background of the sea surface when viewed from below. It attains the squid more difficult to see by predators looking for the molluscs from deeper depths.

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