Fungi as a separate kingdom of life were classified merely 5 decades ago, i.e. in 1969 when the American plant ecologist Robert Whittaker proposed his five-kingdom system of classification of the biota. Before that, fungi were considered low-level plants. The separation of fungi came into existence when scientists saw that the nutritional mechanisms of fungi were more similar to that of animals than to plants, thanks to molecular methods for phylogenetic analysis. But before that the similarities of morphology, mobility and growth habitats made the scientists and taxonomists believe otherwise. There is a plethora of scientific explanations for why fungi are not plants but in straightforward terms, the cell walls of fungi do not contain cellulose like that of plants, and they do not have xylem and phloem to transfer nutrients and water.
If we look into the diversity of fungi, it is fascinating. They can exist everywhere, in yeast or hyphal forms or sometimes both. UV exposure, deep sea trenches, deserts, radiations, you name it. A black yeast, Hortaea werneckii, is known for and is still being investigated for its remarkable halotolerance, which is the adaptation of living organisms to high salinity. In their research, Dadachova et al. cited that melanized fungi colonized the walls of the highly radioactive damaged walls of Chernobyl and surrounding soils. These findings were supplemented by their principal finding in labs when melanized Cryptococcus neoformans cells were exposed to ionizing radiation approximately 500 times higher than the background grew significantly faster. This is a manifestation of radiographic growth. C. neoformans, in its yeast form, is often found in bird excrement and can infect immunocompetent as well as immunocompromised hosts, for example, a person with AIDS may get fungal meningitis or encephalitis as a secondary infection. However, for normal people (immunocompetent), infections are rare and hence they are known as opportunistic pathogens. In a study to determine whether some severely ignored fungi like lichens* could survive extra-terrestrial UV exposure, two lichen species Rhizocarpon geographicum and Xanthoria elegans were sent to space. It returned after 16 days. When analysed using Confocal scanning microscopy in combination with the use of specific fluorescent probes, the researchers found that all exposed lichens showed the same photosynthetic activity as they showed before the flight. Most fungi grow in terrestrial environments but some grow partly or solely in water. As of 2020, taxonomists have described more than 148,000 species of fungi but that may be just 10% of the kingdom.
Although there are somewhere around 2.2 to 3.8 million species of fungus in the world, only a few hundred of them can affect a human being according to the Centre for Disease Control and Prevention. This is because of the relatively high body temperature of ~37 ℃ which keeps most of them away as they prefer lower temperatures. Another reason is, most fungi are successfully fought by the human immune system. Fungal infections on the skin are very common. For example, Ringworm is a fungal infection and no worm is involved in it. It is related to Athlete’s foot and spreads from skin to skin of an animal or other human beings. Fungal infections of the lungs are more serious and diagnosis and eventual cure can be delayed as symptoms are similar to that of other diseases like bacterial pneumonia or tuberculosis. Infections like Fungal Meningitis or bloodstream infections are rare but can be life-threatening. In contrast to human beings, about 50,000 fungal species infect insects.
We can particularly look into the case of Zombie Ants, where fungi, Ophiocordyceps unilateralis, infect an ant (Camponotus spp. in our case) with spores and drives them crazy. The enthralled ant goes to a damp place where the humidity is optimal for the growth of the fungi. It then bites down on the bark of a tree or the stem of a plant and dies. The fungi then feed on the body, grow its fruiting part out of the dead ant’s head and use the corpse as a launchpad to jettison its spores and infect more ants. Although it deviates from the Zombie Lore as the fungi do not infect the brain, it does control its behaviour and eventually kill it. The controlling of the behaviour of the infected ants is proved by research (Sobczak, et al.), where the researchers observed that the ant dies at a strategically elevated position so that when the stroma bursts, the spores falling can cover a considerable area.
Behavioural changes are also observed in fungi-infected Ghost moths, which inhabit areas 4000m above sea level in the Tibetan plateau (majority), Yunnan province of China, Nepal, Bhutan and Himalayan highlands of India. The moths live for 2-5 days during which they mate and lay eggs but their lifecycle is of about 5 years during which the larvae turn into caterpillars and mostly spend their life underground etching themselves to the roots of grass. Soon after the eggs are hatched, the larvae might get infected by Ophiocordyceps sinensis, whose spores penetrate the still soft larvae’s exoskeleton. Once infected the fungus stays dormant for a period inside the larva, which then turns into a caterpillar. Although O. sinensis has an optimal growth temperature of 18 ℃, it can survive in temperatures lower than -40 ℃ as a psychrophile. The fungus then concentrates on the caterpillar’s lipid reserves, depriving it of nutrients leading to starvation and eventual death. After the death of the caterpillar, the fungus inhabits its body and the fruiting body grows out of its head and comes above ground.
One of the reasons why we have skin fungi is they can get between folds of skin. Those are sort of wet, dark places fungi can proliferate that are cooler than body temperature… As the Earth warms up, there is concern that the change between environment temperature and body temperature won’t be as dramatic…
– Shmuel Shoham, Infectious diseases expert at Johns Hopkins University School of Medicine.
Behavioural changes in human beings due to fungal infection are not yet seen. However, hallucinogenic effects on human beings due to chemicals drawn from fungi are evident. Shrooms or magic mushrooms, used as recreational drugs are usually Psilocybin mushrooms that contain psilocybin which turns into psilocin upon ingestion. Psilocin or 4-hydroxy-N,N-dimethyltryptamine is a serotonergic psychedelic substance which induces psychological effects similar to a sympathetic arousal state along with synesthesia**, restlessness, euphoria, etc. Similar to the effects of Lysergic acid diethylamide (LSD). In the process of synthesis of LSD, Lysergic acid is produced using ergometrine or ergotamine tartrate as a starting material. Ergotamine occurs naturally in ergot fungus (Claviceps purpurea), a common parasitic fungus found on rye grains. However, these are not infections, but rather voluntary (sometimes maybe accidental) ingestions.
According to Shmuel Shoham, an infectious disease expert at John Hopkins University School of Medicine, there is concern that, as the temperature of Earth rises, the change between the body temperature of human beings and the environment temperature will not be as dramatic. Hypothetically that would make it easier for fungi that have evolved to withstand hotter temperatures to infect the human body. Candida auris is one fungal species capable of infecting humans, which scientists suspect, maybe due to rising environmental temperatures. It grows as yeast and causes Candidiasis in humans, often acquired by patients in hospitals due to weakened immune systems. Invasive C. auris infection can cause fungemia and affect the central nervous system and internal organs. It is notorious for its multiple drug resistance and treatment is complicated as it is misidentified as other Candida species.
While the deadly second wave of Covid-19 was ravaging India, doctors were reporting cases of a rare infection – ‘The Black Fungus’. Black fungus or Mucormycosis is a very rare infection. It is caused by exposure to mucor mould which is commonly found in soil, plants, manure, and decaying fruits and vegetables. According to Dr. Akshay Nair, a Mumbai-based eye surgeon, mucor moulds are ubiquitous and are found in soil, air and even in the noses and mucus of healthy people. Doctors believe the infection of mucormycosis might have been triggered by the use of steroids used on critically ill covid-19 patients. Steroids reduce the inflammation in the lungs and help stop some damage to the body when it is fighting off the coronavirus, but it also reduces the immunity of the body and shoots up blood sugar, both in diabetic and non-diabetic patients. This drop in immunity could trigger a mucormycosis infection.
These instances reveal that fungi are not some happy-go-lucky organisms that will spare human beings from a deadly infection. The situation is such that there is no dire need for the kingdom Fungi to evolve and attack human beings. Yet. With the global temperature rising the fungi might evolve and then it will be a whole new discussion. But what now? Fungi are the most rarely studied organisms. As mentioned earlier that it is likely that there are about 3 million species of fungi. But some believe it can go up to 5 million. Therefore, it is important that while other organisms and diseases are studied, fungi should be given equal importance and studied. Although organisations are working to put a stop to or minimize global warming, it is unlikely that it will stop, let alone reverse. Studies on fungi might work out a way to traverse one eventuality.
*Lichens are composite organisms that arise from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.
**Synesthesia is when you hear colours or you see music
References
- Vaupotic, Tomaz, et al. “Mitochondrial Mediation of Environmental Osmolytes Discrimination During Osmoadaptation in the Extremely Halotolerant Black Yeast Hortaea Werneckii.” Fungal Genetics and Biology, vol. 45, no. 6, Elsevier BV, June 2008, pp. 994–1007. https://doi.org/10.1016/j.fgb.2008.01.006.
- Dadachova, Ekaterina, et al. “Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi.” PLoS ONE, edited by Julian Rutherford, vol. 2, no. 5, Public Library of Science (PLoS), May 2007, p. e457. https://doi.org/10.1371/journal.pone.0000457.
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- Sobczak, JF. “The Zombie Ants Parasitized by the Fungi Ophiocordyceps Camponotiatricipis (Hypocreales: Ophiocordycipitaceae): New Occurrence and Natural History.” Mycosphere, vol. 8, no. 9, Mushroom Research Foundation, 2017, pp. 1261–66. https://doi.org/10.5943/mycosphere/8/9/1.
- Pontoppidan, Maj-Britt, et al. “Graveyards on the Move: The Spatio-Temporal Distribution of Dead Ophiocordyceps-Infected Ants.” PLoS ONE, edited by Anna Dornhaus, vol. 4, no. 3, Public Library of Science (PLoS), Mar. 2009, p. e4835. https://doi.org/10.1371/journal.pone.0004835.
- Xia, En-Hua, et al. “The Caterpillar Fungus, Ophiocordyceps Sinensis, Genome Provides Insights Into Highland Adaptation of Fungal Pathogenicity.” Scientific Reports, vol. 7, no. 1, Springer Science and Business Media LLC, May 2017, https://doi.org/10.1038/s41598-017-01869-z.
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- Europen Monitoring Centre for Drugs and Drug Addiction [Europen Monitoring Centre for Drugs and Drug Addiction]. “Lysergide (LSD) Drug Profile.” https://www.emcdda.europa.eu/publications/drug-profiles/lsd, Europen Monitoring Centre for Drugs and Drug Addiction, www.emcdda.europa.eu/publications/drug-profiles/lsd. Accessed 28 Jan. 2023
- Gibbens, Sarah. “Could a Parasitic Fungus Evolve to Control Humans?” Science, 24 Jan. 2023, www.nationalgeographic.com/science/article/parasitic-fungus-evolve-to-control-humans.
- Biswas, By Soutik. “Mucormycosis: The ‘black Fungus’ Maiming Covid Patients in India.” BBC News, 9 May 2021, www.bbc.com/news/world-asia-india-57027829.