Tristan Wang ‘16, THURJ Staff

When it comes to naturally illuminated objects, people can be a lot like flies—they are attracted to the dim glows of nature. Brilliant jellies, fireflies, fish and algae have all captured the imagination of humans, embedding themselves into folklore across a variety of cultures; and fungi should by no means be left out. The phenomenon of glowing, referred to as bioluminescence, is the radiation of cold visible light by living organisms. It is not uncommon to find faint glows not only in animals like insects, jellyfish and fish, but also in bacteria, dinoflagellates and fungi (1). While only a handful of fungal species are able to emit light, those that do have boggled the minds of scientists. The mysteries behind the mechanisms and ecology of fungal bioluminescence are numerous, but researchers have been able to apply the “glowing” characteristics of these critters to a variety of causes including bioremediation and medicine.

Phylogeny

Currently, there are about 71 known species of bioluminescent fungi spread across four distinct lineages including Mycenoid, Omphalotus, Lucentipes, and Armillariia, all of which are within the large order Agaricales that includes over 9000 species within the greater phyla of Basidiomycota (2). Of these four mushroom-forming divisions, most bioluminescent fungi are saprotrophic white-rot fungi, feeding on dead organic matter, although some are known to be disease causing in plants (2,3). These specimens are usually found in the warmer humid climates of tropical and temperate areas (3). One species Panellus stipticus is unusual in that only North American strains appear to be luminescent (1).

Chemistry Behind the Glow

Luminescence in fungi occurs through an enzyme-catalyzed reaction that involves some form of enzyme acting on a substrate, generically termed luciferin and luciferase respectively in bioluminescent organisms (1). Luciferin structure differs depending on the organism it comes from, but all known luciferins become oxidized in the presence of the appropriate luciferase, resulting in an excited state. In fungi, this process occurs during both the day and night, emitting a light of about 530 nm maximum wavelengths in both the vegetative body (mycelia) and the fruiting bodies (4). Yet despite knowing this, scientists have not found an exact chemical pathway to describe fungal luminescence (4).

Having evolved independently in several ancestries, bioluminescence does not in general use the same structure of luciferin and luciferase in all illuminating organisms (2). In fact, the primary commonality among these lineages is that bioluminescence requires the presence of oxygen in order to work (1). For fungi however, it is a different story. Recent research, through the testing of luciferins and luciferases from different bioluminescent lineages, showed that all four fungal lineages share the same type of substrates and enzymes (2). This suggests that there was a single evolutionary origin of luminescence, at least among fungi species.

Explaining the Light

Functionally, scientists know little about the role of fungal bioluminescence. Because fungi are unable to detect their own light or the light of others, it is thought that this illumination likely affects interactions with other organisms instead (3). One theory states that luminescence helps in attracting invertebrate fungivores to help with spore dispersal (1). This claim is reinforced by the fact that the gills and spores of luminescent species shine the brightest (1). In addition, by closing off luminescent specimens in glass tubes, biologists have modeled a dark night scenario and found that arthropods were more attracted to luminescent species than they were to non-luminescent species (5).

The theory of spore-dispersal of course does not explaint why there is bioluminescence throughout the fungal body however, including in the mycelia, the hair-like vegetative body that does not play a role in spore formation. It is thought that some fungivores that feed on the mycelia are repelled by the emission of light or that individual fungi cannot simply contain bioluminescence in one part of the organism (1). It seems that further research will have to be done to illuminate the answers to these questions.

One interesting approach to understanding fungal bioluminescence also happens to be the simplest. It is possible that bioluminescence is not an intended effect of fungal growth and that it is simply a by-product of a biochemical reaction that occurs naturally in fungi (1). Some scientists think that bioluminescence could help in the degradation of lignin (a tough polymer that gives plants structure) by aiding to detoxify peroxides formed during this decomposition (1).

Applications

Several researchers have found ways to apply the luminescent abilities of certain fungi in chemical testing for toxins, a process referred to as a bioassay. Because many toxins have identifiable impacts on fungal growth and bioluminescence, their concentrations can be estimated through observation of the fungal specimens. Certain species react to particular toxins such as pentachlorophenol (PCP), copper and zinc, as there is often a reduction of light production with higher concentrations of pollutants (6). Thus, these species may play a future role in bioremediation and detection of pollutants.

In addition, bioluminescent fungi have also been reported to be useful in real-time monitoring of certain fungal infections (7). Microbial infections within animals can be observed to study progressions of disease in terms of space and time and the effectiveness of treatment (7). Light discharge from the luciferin may therefore help in detection of these fungal diseases.

As intriguing as it is mysterious, fungal bioluminescence is a field of research still in need of work. While little is known about the chemical and ecological properties of these mushrooms, biologists have still been able to find uses for this bioluminescence in bioremediation and disease detection. In folklore, we often find that fungal bioluminescence played on the minds of the curious in the past and it seems that the same applies for researchers today.

References

  1. Weitz, Weitz Hedda J. “Naturally Bioluminescent Fungi.” Mycologist 18.1 (1999): 4-5
  2. Oliveira, Anderson G., Dennis E. Desjardin, Brian A. Perry, and Cassius V. Stevani. “Evidence That a Single Bioluminescent System Is Shared by All Known Bioluminescent Fungal Lineages.” Photochemical & Photobiological Sciences 11.5 (2012): 848.
  3. Stevani, Cassius V., Anderson G. Oliveira, Luiz F. Mendes, Fernanda F. Ventura, Hans E. Waldenmaier, Rodrigo P. Carvalho, and Tatiana A. Pereira. “Current Status of Research on Fungal Bioluminescence: Biochemistry and Prospects for Ecotoxicological Application.” Photochemistry and Photobiology 89.6 (2013): 1318-326.
  4. Mori, Kenichi, Satoshi Kojima, Shojiro Maki, Takashi Hirano, and Haruki Niwa. “Bioluminescence Characteristics of the Fruiting Body of Mycena Chlorophos.” Luminescence 26.6 (2011): 604-10.
  5. Desjardin, Dennis E., Anderson G. Oliveira, and Cassius V. Stevani. “Fungi Bioluminescence Revisited.” Photochemical & Photobiological Sciences 7.2 (2008): 170.
  6. Weitz, Hedda J., Colin D. Campbell, and Ken Killham. “Development of a Novel, Bioluminescence-based, Fungal Bioassay for Toxicity Testing.” Environmental Microbiology 4.7 (2002): 422-29.
  7. D’Enfert, Christophe, Anna Vecchiarelli, and Alistair J.p. Brown. “Bioluminescent Fungi for Real-time Monitoring of Fungal Infections.” Virulence 1.3(2010): 174-76.

Comments:

NO COMMENTS

LEAVE A REPLY