Bioluminescence In Fungi

Introduction

What is Bioluminescence?

The main focus of the current paper is on bioluminescent fungi, but the basic features of bioluminescence discussed are common to all bioluminescent organisms.

Bioluminescence is simply light created by living organisms. Probably the most commonly known example of bioluminescence by North Americans is the firefly, which lights up its abdomen during its mating season to communicate with potential mates. This bioluminescent ability occurs in 25 different phyla, many of which are totally unrelated and diverse, with the phylum Fungi included in this list.

One of the features of biological light that distinguishes it from other forms of light is that it is cold light. Unlike the light of a candle or a lightbulb, bioluminescent light is produced with very little heat radiation. This aspect of bioluminescence especially interested early scientists who explored it.

The light is the result of a biochemical reaction in which the oxidation of a compound called “Luciferin” is catalyzed by an enzyme called “Luciferase”. The light generated by this biochemical reaction has been utilized by scientists as a bioindicator for tuberculosis as well as heavy metals. Ongoing research involving bioluminescence is currently underway in the areas of evolution, ecology, histology, physiology, biochemistry, and biomedical applications.

History of Bioluminescent Fungi

The light of luminous wood was first noted in the early writings of Aristotle, which occurred in 382 B.C. (Johnson and Yata 1966 and Newton 1952). The next mention of luminous wood in literature occurred in 1667 by Robert Boyle, who noticed glowing earth and noted that heat was absent from the light.

Many early scientists, such as Conrad Gesner, Francis Bacon, and Thomas Bartolinall, observed and made notations of luminous earth (Johnson and Yata 1966 and Newton 1952). These early observers thought that the light was due to small insects or animal interactions. The first mention that the light of luminous wood was due to fungi occurred from a study of luminous timbers used as supports in mines by Bishoff in 1823. This opened the way for further study by many other scientists, and by 1855 modern experimental work began by Fabre (Newton 1952).

Fabre established the basic parameters of bioluminescent fungi, those being:

• The light without heat
• The light ceased in a vacuum, in hydrogen, and carbon dioxide
• The light was independent of humidity, temperature, and light, and did not burn any brighter in pure oxygen

The work by Herring (1978) found that the luminescent parts of the fungus included the pileus (cap), hymenium (gills), and the mycelial threads in combination or separately (Figure 2). Also, the individual spores were seen to be luminescent.

Herring also stated that if the fruiting body (mushroom) was bioluminescent, then the mycelial threads were always luminescent as well but not vice versa.

From the 1850s to the early part of the 20th century, the identification of the majority of fungal species exhibiting bioluminescent traits was completed. The research of bioluminescent fungi stagnated from the 1920s until the 1950s (Newton 1952 and Herring 1978). After which extensive research began involving the mechanisms of bioluminescence and is still carried out to the present.

The Process of Bioluminescence

Bioluminescence results because of a certain biochemical reaction. This can be described as a chemiluminescent reaction, which involves a direct conversion of chemical energy transformed into light energy (Burr 1985, Patel 1997, and Herring 1978).

The reaction involves the following elements:

Enzymes (Luciferase) – biological catalysts that accelerate and control the rate of chemical reactions in cells. Photons – packs of light energy. ATP – adenosine triphosphate, the energy-storing molecule of all living organisms. Substrate (Luciferin) – a specific molecule that undergoes a chemical charge when affixed by an enzyme. Oxygen – as a catalyst

A simplified formula of the bioluminescent reaction:

ATP (energy) + Luciferin (substrate) + Luciferase (enzyme) + O2 (oxidizer) = light (photons)

The bioluminescent reaction occurs in two basic stages:

The reaction involves a substrate (D-Luciferin), combining with ATP and oxygen, which is controlled by the enzyme (Luciferase). Luciferins and Luciferase differ chemically in different organisms but they all require molecular energy (ATP) for the reaction. The chemical energy in stage one excites a specific molecule (The Luminescent Molecule: the combining of Luciferase and Luciferin).

The excitement is caused by the increased energy level of the luminescent molecule. The result of this excitement is decay, which is manifested in the form of photon emissions, producing the light. The light given off does not depend on light or other energy taken in by the organism and is just the byproduct of the chemical reaction and is therefore cold light. The bioluminescence in fungi occurs intracellularly and has been noted at the spore level (Burr 1985, Newton 1952, and Herring 1978).

This may at times be mistaken for an extracellular source of light, but this is due to the diffusion of the light through the cells of the fungus. In examining the photograph in figure 1, it appears that the cap of the fungus is glowing, but after study, it was observed that just the gill structures emit the light and the cap (which is thin) emits the light of the gills by diffusion (Herring 1978).

The energy in photons can vary with the frequency (color) of the light. Different types of substrates (Luciferins) in organisms produce different colors. Marine organisms emit blue light, jellyfish emit green, fireflies emit greenish-yellow, railroad worms emit red, and fungi emit greenish-bluish light (Patel 1997).

Fungal Families Exhibiting Bioluminescence

The phylum Fungi is composed of the following 5 divisions (Newton 1952):

1. Myxomycetes (slime molds)
2. Schizomycestes (bacteria)
3. Phycomycetes (molds)
4. Ascomycetes (yeasts, sac fungi, and some molds)
5. Basidiomycetes (smuts, rusts, and mushrooms)

Of the above divisions, the majority of bioluminescence occurs in the Basidiomycetes, and only one observation has been made involving the Ascomycetes; specifically, in the Ascomycete genus Xylaria (Harvey 1952).

At present, there are 42 confirmed bioluminescent Basidiomycetes that occur worldwide and share no resemblance to each other visually, other than the ability to be bioluminescent.

Of these 42 species that have been confirmed, 24 of them have been identified just in the past 20 years, and as such, many more species may exhibit this trait but are yet to be found. The two main genera that display bioluminescence are the genus Pleurotus, which has at present 12 species occurring in continental Europe and Asia, and the genus Mycena, which has 19 species identified to date with a worldwide distribution range.

In North America, only 5 species of bioluminescent Basidiomycetes have been reported. These include the Honey mushroom – Armillaria mellea (illustrated in Figure 3), the common Mycena – Mycena galericulata (illustrated in Figure 1), the Jack O’Lantern – Omphalotus olearius (pictured in Figure 4), Panus stipticus, and Clitocybe illudens.

The question of whether bioluminescent mushrooms were all poisonous was raised in the discussions between my laboratory partner and myself. After examining the literature and a mushroom field guidebook, it was evident that there was no correlation between the edibility of the mushroom and its bioluminescence. Some mushrooms, such as Armillaria mellea, the Honey mushroom, were listed as being excellent to eat.

While the Jack O’Lantern – Omphalotus olearius was listed as poisonous and caused severe gastrointestinal cramps, the edible merits of the common Mycena were unknown. And while Panus stipticus was listed as poisonous, it was found to contain a clotting agent and useful in stopping bleeding (Lincoff 1981, Newton 1952, and Herring 1978). As only a field guide to North American mushrooms was available, only the North American varieties were examined. If all 42 species of bioluminescent Basidiomycetes were included in the search, a possible correlation may have been found.

Bioluminescence Research Applications

Luminescence has unique advantages for scientific studies as it is the only biochemical process that has a visible indicator that can be measured. The light given off in the bioluminescent reaction can now be accurately measured with the use of a luminometer. This ability to easily and accurately detect small amounts of light has led to the use of the bioluminescent reaction in scientific research involving biological process applications. The following are just a few applications, some of which have been developed in only the last few years (Johnson and Yata 1966 and Patel 1997). The following are two examples that have been recently developed.

The Tuberculosis Test

Testing for tuberculosis has long been a problem because of the long time it takes for the species to grow to a size that is detectable by modern medicine. Typically, growing a culture of Mycobacterium tuberculosis large enough to determine the strain that a particular patient has can take up to three months. Of course, this poses a problem because the patient often cannot wait for the diagnosis and must be given drugs that his strain may be resistant to.

This is further complicated because there are 11 drugs used to combat TB, picking the right one before determining the strain has a 1/11 chance of success. Recently, a way of incorporating bioluminescence into the TB tests has been found and can sharply reduce the diagnosis time to as little as 2 days. The technique involves inserting the gene that codes for luciferase into the genome of the TB bacterial culture taken from the patient.

The gene is introduced through a viral vector and once incorporated, the bacteria produces the luciferase. When luciferin is added to the culture, light is produced. Since less than 10,000 bacteria are needed to code for enough luciferase to produce a detectable amount of light, the culture time is reduced to only 2-3 days. Since the luciferase-luciferin reaction requires ATP, the resistance of the strain in the culture can be tested by adding a drug and watching for light.

This will indicate which of the 11 drugs therapies will be effective in treating Tuberculosis. By reducing the time needed to prescribe the correct drugs for treatment, this application of bioluminescence will someday be ready to save some of the 3 million killed each year by tuberculosis (Patel 1997).

Biosensors

Bioluminescence has also been used for several years as a biosensor of many substances. As seen in the tuberculosis example, bioluminescence can be used as a sensor for the presence of ATP because ATP is needed in the light producing reaction. Other techniques have been used for detecting ions of mercury and aluminum, among others, by using bacteria with light genes fused to their ion-resistant regulons.

For example, if a bacteria that is resistant to Hg is in the presence of Hg, the genes coding for its Hg resistance will be activated. The activation of that gene will also activate the luciferase gene fused to it, so the bacteria will produce luciferase whenever Hg is present. Adding luciferin and testing for light production with a luminometer reveals the presence of the metal ion in the solution. This technique is especially useful in testing for pollutants in the water supply when concentrations are too low to detect by conventional means (Herring 1978 and Patel 1997).

Other areas that are currently using bioluminescence in scientific research include evolution, ecology, histology, physiology, biochemistry, biomedical applications, cytology, and taxonomy. Any area that involves a living organism can utilize bioluminescent technology as a biosensor.”

Conclusion

The glow generated by bioluminescent fungi has, for centuries, generated interest from philosophers and scientists, and has benefited science by providing problems to solve. How does it work, and does it have a practical application?

The answers to these basic problems have been discovered today and have resulted in benefiting mankind by bettering our lives, especially in regard to its biomedical applications. Further research with bioluminescent fungi is being conducted on a worldwide scale and includes North America, Japan, and Europe. Future research may lead to new discoveries and uses for bioluminescent organisms, such as the fungi group.

References

1. Burr, G.J. 1985. Chemiluminescence and Bioluminescence. Marcel Dekker, Inc. NewYork, U.S.A.
2. Johnson, F. H. and Yata, H. 1966. Bioluminescence in progress. Princton, NewJersey, Princeton University Press.
3. Lincoff,G.H. 1981. The Audubon Society field guide to North American Mushrooms.
4. Knopf Inc. New York. U.S.A.
5. Newton, H.E. 1952. Bioluminescence. Academic Press. New York. U.S.A.
6. Herring, P.J. 1978. Bioluminescence in Action. Academic Press. New York. U.S.A.
7. Patel, P.Y. 1997. Bioluminescence in scientific research. Jan 10, 1997.
8. Http://www. emailprotectedWood, M.F. and Stevens, F. 1997. The Myko web page -Fungi Photos. Jan 10, 1997.
9. . http://www.mycoweb.com/ba_index.html#AWED. AM GROUP BIOLOGY 201 BIOLUMINESCENT FUNGI DUE MARCH 7, 1997