The curious underworld of fungi

By Ceara Harper

Fungi have been around for 1 billion years and will not be making an exit anytime soon. They are in the air we breathe, the food we eat, the ground we stand on and are entangled within our bodies. Fungi are essential to life on earth (as we know it) but are also capable of annihilating it.

In 2019, researchers discovered multicellular microfossils that date back 1,010–890 million years ago (Loron et al., 2019), almost half a billion years earlier than previously established for fungal life on dry land, as well as being the earliest fossils found for any multicellular life on land. These eukaryotes were named by researchers as Ourasphaira giraldae and were present in the early Neoproterozoic Era, which was the last era in the Precambrian supereon. Skip 530 to 740 million years later, in the Middle Ordovician to late Devonian period, and Prototaxites grew to the size of two storey buildings, dwarfing all other land-life of the time. These fungi had a homogenous tissue built from 5 – 50 micrometre in diameter interwoven tubes (Boyce et al., 2007), unlike any other organism. Jump the clock to modern day and it is estimated that 2.2 – 3.8 million species of fungi exist with 97 – 92% being unidentified (Hawksworth and Lucking, 2017). Fungi are extremely versatile and can be used as a food source, in the preparation of food (such as fermentation processes); in pest control as natural pesticides, or to produce antibiotics; such as penicillin, or even genetically engineered to produce human hormones, such as insulin. Recently, psilocybin fungi have been found to potentially alleviate major depressive disorder, when used as an assist to therapy (Davis et al., 2020).

Perhaps surprisingly, without a mycorrhizal relationship with fungi, many grasses and trees would not be able to survive. The first land plants had no real roots and were only able to survive due to this symbiotic relationship (Smith and Read, 2008). In fact, Mycorrhizal fungi, a diverse range of different fungal taxa, are associated with the roots of more than 90% of all plant species (Bonfante and Genre, 2010). Most of these fungi uphold a mutualistic symbiotic relationship with plants by increasing the plant’s nutrient uptake. This is achieved by nutrient absorption through the fungal mycelium, which is then used to supply the plant via a specialised symbiotic fungi-plant interface. In return, the fungi are able to grow and reproduce off the root of the plant, as without this, they would be unable to access organic carbon needed for sugars and lipids (Smith and Read, 2008). Not only do fungi and plants have one-to-one interactions, but it has been found that there are extensive networks of hypha throughout the soil that allow transfer of nutrients horizontally between fungi to fungi and thus plant to plant; this is known as the wood-wide web (Helgason et al., 1998). In this way, mycorrhizal fungi play a major role in the development and conservation of global ecosystems (Field et al., 2020), which is especially important at current, considering the unravelling of the climate crisis and ecological breakdown.

However, there are many parasitic relationships between fungi and plants, or fungi and animals as well. Fungi can destroy growing and stored food with deft speed. Phytophthora infestans is the name given to the fungus responsible for wiping out 1 million of the Irish population between 1845-1849 during the Great Famine; a fungus that led to a permanent alteration of Ireland’s demographic as well as its cultural and political landscape. Whilst Panama disease, caused by Fusarium oxysporum f.sp. cubense, which is resistant to fungicides, is one of the most deadly diseases for plants of modern times (Stover, 1962). This fungus threatens to wipe out the Cavendish banana – which makes up 99% of all banana shipments worldwide (Sheldrake, 2020). Fungi do not stop at plants; the cytrid fungus is currently causing the extinction of many amphibians, with 90 species already wiped out as a result (Sheldrake, 2020). While fungal diseases affecting humans range from manageable to life threatening, such as invasive candidiasis, caused by Candida auris, that can infect the blood, brain and heart of patients with weakened immune systems (Kullberg and Arendrup, 2015).

This article has hardly scratched the surface of the far-reaching effects that fungi can have on people, plants and the planet, with so much left still not understood about this neglected yet colourful and versatile underworld.

References:

Alan K. Davis, PhD1,2; Frederick S. Barrett, PhD1; Darrick G. May, MD1; et al. Published online November 4, 2020. Effects of Psilocybin-Assisted Therapy on Major Depressive Disorder. JAMA Psychiatry doi:10.1001/jamapsychiatry.2020.3285

Bonfante, P., Genre, A. Mechanisms underlying beneficial plant–fungus interactions in mycorrhizal symbiosis. Nat Commun 1, 48 (2010). https://doi.org/10.1038/ncomms1046

Boyce, K.C.; Hotton, C.L.; Fogel, M.L.; Cody, G.D.; Hazen, R.M.; Knoll, A.H.; Hueber, F.M. May 2007. “Devonian landscape heterogeneity recorded by a giant fungus”. Geology. 35 (5): 399–402. doi:10.1130/G23384A.1.

Hawksworth D.L., Lücking R.. Fungal Diversity Revisited: 2.2 to 3.8 Million Species, Microbiology Spectrum, July 2017 vol. 5 no. 4 doi:10.1128/microbiolspec.FUNK-0052-2016

Helgason, T., Daniell, T.J., Husband, R., Fitter, A.H. & Young, J.P.W. Ploughing up the wood-wide web? Nature 394, 431 (1998).

Kullberg BJ, Arendrup MC. Invasive Candidiasis N Engl J Med 2015; 373:1445-1456.

Loron, C.C., François, C., Rainbird, R.H. et al. 2019. Early fungi from the Proterozoic era in Arctic Canada. Nature 570, 232–235 (2019). https://doi.org/10.1038/s41586-019-1217-0

Sally E. Smith, David Read, 2008. Mycorrhizal Symbiosis (Third Edition), Academic Press, Pages 1-9, ISBN 9780123705266, https://doi.org/10.1016/B978-012370526-6.50002-7.

Sheldrake M., 2020, Entangled Life, Penguin Books.

Stover, R. H. 1962. Fusarial Wilt (Panama Disease) of Bananas and Other Musa Species. CMI, Kew, Surrey, UK.

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