The term ‘radiotropism’ refers to the ability of several fungal species to harvest usable energy from forms of ionizing radiation, such as gamma radiation emitted from nuclear reactors.
Ionizing radiation is emitted from high-energy sources and is composed of particles that carry enough energy to liberate electrons from an atom’s orbit upon interaction with said atom. In this event, the chemical bonds in the atom can be changed, producing ions that may be especially reactive. As this is generally thought to inflict great chemical and biological damage on living organisms, the existence of radiotrophic fungi that can harvest the energy present in ionizing radiation lends itself to the exciting exploration of novel ways by which organisms can sustain themselves.
Could these fungi be used to help astronauts?
Another high radiation environment where fungi have adapted is orbiting spacecraft.
Analysis of the atmosphere in the Russian orbital station Mir revealed the ubiquitous presence of many microorganisms. Fungal contamination poses certain threats to the well-being of the crew, not only because some of those fungi are potential human pathogens but also because fungi possess powerful enzymatic systems and secrete various metabolites capable of degrading structural materials inside the spacecraft, from polymers to various alloys.
The survey of the environmental contamination on board the International Space Station (ISS) revealed many fungal species on the surfaces and in the air, including Aspergillus sp. The levels of ionizing radiation that these fungi encounter in the space stations—approximately 4 cGy per year—are not fungicidal and allow fungi to thrive, provided the humidity levels are sufficient.
Interestingly, many of the microorganisms inhabiting the space station—both bacteria and fungi—were found to be pigmented or melanized, which hints at the usefulness of pigments presence in those cells under extreme conditions.
Well, what about cancer?
Physicists Venkateswaran and Wang, whose job it is to help isolate, classify, and purify everything they discover, think these fungi could be used for such treatments. If the couple discovers that the fungus produces new products depending on the amount of radiation, it could be turned into a drug. Venkateswaran believes that these drugs could be used as radiation "disruptors" in humans, such as cancer patients undergoing radiation treatment, workers at nuclear power plants like Chernobyl, or NASA astronauts on long-haul flights. There are other radioprotective drugs currently available, but the American Cancer Society considers this an area of research that should be further studied. Fungi in general have a history of producing medicinal properties such as "secondary metabolites' ' - substances that the fungus does not need to function but is produced when needed for survival - and can be converted into drugs. For example, lovastatin, the active ingredient in many cholesterol medications, and cyclosporine, an immunosuppressant used during organ transplants, are both compounds made by fungi. Overall, this may be the future of medicine and biological advancements.
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