A Fungus that has Radiation on the Menu

 Kevin Mamo

Professor Horgan 

HST - 401 A

December 10th, 2022

A Fungus that has Radiation on the Menu

Normally when organisms come in contact with gamma radiation it usually ends up in a disastrous situation resulting in said organisms death. However, one mushroom doesn’t have such vulnerability and actually thrives in radioactive environments. The radiotrophic fungus known by researchers as Cryptococcus neoformans was first discovered in one of the harshest environments on the planet, the Chernobyl nuclear power plant in northern Ukraine. 

Chernobyl is home to one of the worst nuclear disasters in recorded history which occurred over thirty years ago on April 26th, 1986. One of the nuclear reactors, reactor four, had a sudden power surge due to flawed control rod design as the Soviets used graphite slabs to regulate heat in between rods. This meant the reactors had to routinely be put in low power intervals in order to stay cool, so that combined with miscommunication by reactor technicians caused the reactor meltdown/explosion. According to Soviet scientists reactor four released around 190 metric tons of uranium dioxide fuel and fission products into the atmosphere. Fortunately, of over the one hundred radioactive elements released by the explosion most of them fizzled out quickly therefore losing their radioactivity. Nonetheless, two of the radioactive isotopes Strontium-90 and Caesium-137 are still found in and around the Chernobyl reactors. 

On average it takes a radioactive isotope anywhere from five to ten decay cycles for it to be deemed safe and no longer radioactive.  Strontium-90 and Caesium-137 have half-lives of 29 years and 30 years respectively. It has only been 36 years since the disaster, meaning that both the Strontium and Caesium isotopes haven’t even gone through their second decay cycle yet. This shows that the environment in Chernobyl is not only dangerous but it is also prolonged by the long half-lives of the elements found in the area. 

Despite all of those obstacles, scientists discovered the fungus Cryptococcus neoformans in 1991. They noticed scores of dark mushrooms growing in the still water surrounding the reactors, and on the walls of the reactors themselves growing towards the inner portion of the reactor where the radiation is much more potent. Scientists proved that the mushrooms were radiotrophic by using the return-angle method. Essentially the return-angle method is done by taking a sample of the fungus and putting it in a controlled system, and then a radioactive particle is placed in the same enclosure as the fungus. There is a 90 degree vertical line drawn on the same axis as the mushroom and then the experiment begins. If the fungus grows to the left of the 90 degree line (0-90 degrees) towards the radioactive particle then it is radiotrophic and if it grows to the right (>90 degrees) then it is not radiotrophic. 

Not only did researchers confirm that the fungus was radiotrophic, but they also discovered that the reason the mushrooms were so dark in color was because of the high concentration of melanin within them. The melanin inside the fungus plays a critical role in its ability to “eat” ionizing radiation. Melanin is a unique biological compound as it is the only one that is able to take in gamma radiation and convert it into usable energy.

This process is called radiosynthesis and it is very similar, in fact, to photosynthesis. During photosynthesis a plant uses its chloroplasts to take in CO2, water, and sunlight and with the calvin cycle and light-dependent reactions it produces glucose (chemical energy) and oxygen. Radiosynthesis is similar in the sense that melanin acts as the chloroplasts by taking in ionizing radiation and transforming it into chemical energy that the mushroom can then use to grow. It is simpler to think of melanin as an energy transductor as it takes in one form of energy and turns it into another. 

So scientists know that the fungal melanin is good at taking in high amounts of energy and dissipating it quickly, and that it is responsible for the mushrooms’ ability to survive in areas plagued by radiation. Unfortunately, scientists do not know how the melanin is able to do it, as in they cannot explain why melanin can transduce radiation. There is no term or cycle currently discovered/thoroughly researched, such as the calvin cycle, that can better explain the radiosynthesis process. The one observation researchers have made is that melanin’s unique and complex molecular structure allows it to take in the radiation and switch it to chemical energy. 

The Cryptococcus neoformans fungus is definitely an evolutionary wonder, but it is not just some plant that has a quirky feature. The melanin inside the mushrooms can be helpful to humans, surprisingly, and we can utilize the melanin by eating the mushrooms themselves. The average person would think that consuming radiotrophic mushrooms is harmful due to the fact they [mushrooms] are intaking large amounts of radiation but it is completely safe. There is a difference between things that are radioactive and things that are irradiated. Radioactive materials contain unstable atoms that are releasing ionizing radiation due to the excess protons and neutrons in the atom's nucleus. However, objects that are irradiated only come in contact with radiation; it doesn't make them radioactive. In fact most of the meat, poultry, produce, and vegetables we eat are irradiated due to radiation’s efficiency in exterminating microorganisms and insects hiding within our food. The FDA (Food & Drug Administration) utilizes this process to make our food safer, “Food irradiation (the application of ionizing radiation to food) is a technology that improves the safety and extends the shelf life of foods by reducing or eliminating microorganisms and insects. Like pasteurizing milk and canning fruits and vegetables, irradiation can make food safer for the consumer.” 

Scientists first discovered that consumption of the mushrooms could benefit humans by conducting multiple experiments on mice in a controlled environment. The American Society For Microbiology reports, “Mice given fungal melanin are capable of surviving lethal doses of gamma irradiation, presumably as a result of the pigment protecting the digestive tract and associated lymphatic tissue.”  This observation has led to other biologists and researchers suggesting many different applications for the mushrooms. The most common being space exploration/living, military expeditions, and or aiding cancer patients under radiation therapy. While astronauts are in space they are exposed to high levels of radiation due to being outside of earth’s atmosphere, so one of the proposed ways to assist them is by having them consume these radiotrophic fungi. The melanin from the mushrooms would theoretically protect the humans from UV rays the same way it protected the mice in the experiments. 

The other, less useful application, is to have soldiers consume the mushrooms in order to be protected from radiation when on any expedition or infantry dependent mission. However, this doesn’t seem very practical as most missions that require infantry will not have people purposefully going into sites that have high levels of radiation. In addition, while yes it could protect soldiers if they were, unfortunately, caught in a nuclear explosion, in that case the explosion and sheer heat would prove lethal enough to harm any soldier in the area. It would provide safety for troops, but it is such a niche and unlikely situation that the mushrooms would be better used in different ways to maximize their unique properties. 

One of the more beneficial applications for the fungal melanin would be to have cancer patients undergoing radiation therapy consume them. Ekaterina Dadachova, a pharmacy and nutritionist researcher, explains how it can be helpful to said patients, “If a person develops cancer and they go for radiation therapy, they sometimes lose the ability to eat, to swallow, because of the side effects of radiation, said Dadachova, adding that melanin could help protect the fragile organs of the digestive system.” Many of the radiation patients starve not only due to lack of appetite but due to the inability to eat. There could be a way to extract the melanin although it hasn’t been expanded upon or explored much, but doctors may pulverize the mushrooms in order to make it easier for consumption. Since cancer is such a huge problem, and many of its treatments come with so many unwanted side effects, the radiotrophic fungus could prove to be extremely helpful in the healthcare industry. This is a problem that is common and affects everyday people, unlike space travel and military expeditions, most of the research should be focused on this use of the mushrooms because it could genuinely help thousands if not millions of people. 

The radiotrophic fungus is a prime example of how bizarre evolution is. This mushroom was placed in one of the most toxic and dangerous environments and yet it still found a way to naturally combat/resist the surrounding dangers. Perhaps one mushroom had a genetic mutation which created this resilient melanin and only the melanated fungi proceeded to grow while the others died out. This would make sense as radiation does damage and alter cells along with the DNA within said cells, or maybe this gene remained dormant and was activated due to the influx of radiation. Whatever the reason, this mushroom has proven that genetics and evolution are an integral part of life.