Fungi: The secret kingdom we don’t see

As this year’s SCINEMA International Science Film Festival draws ever closer Annamaria Talas, director of SCINEMA 2018 Best Film award winner The Kingdom – How fungi made our world, takes us on an enlightening exploration of the wonderous world of fungi.

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They range in size from microscopic yeast to the largest organism alive – the honey fungus Armillaria solidipes whose underground network spans 1662 football fields! After bacteria, fungi are the most ancient land-based life. According to the latest estimate from mycologist Mary Berbee of the University of British Columbia, they’ve been here for about a billion years, predating the first land plants by at least 500 million years.

They eked out a living mining rocks, extracting minerals, dining on bacteria and fighting them for scarce resources. They became masters of survival.

And then around 450 million years ago, a group of green algae splashed up on to the shoreline. Fungi extended a helping hand, sending their filaments into the plant’s tissue to provide them with a lifeline for water and minerals. The algae repaid the favour by providing sugar.

The relationship was remarkably intimate: the fungal filaments penetrated the very cells of the plant, forming a tree-like structure that’s known as ‘arbuscular mycorrhiza’. Just how this interspecies collaboration was established has been an enduring secret of nature.

The mystery was solved in 2015 when evolutionary microbiologist Pierre-Marc Delaux, now at Université Paul Sabatier, Toulouse, revealed that the algal ancestors of land plants, a group called ‘charophytes’, were equipped to communicate with fungi well before they encountered them.

Unlike other algae, these charophytes possessed a unique set of ‘signalling’ genes. This enabled them to detect and work with these co-operative fungi. Ever since, nearly every land plant has been nurtured by its symbiotic fungi.

The greening of land set in motion a trajectory that led to the richness of life around us. Working with fungi, the first plants changed the atmosphere and sparked the evolution of terrestrial ecosystems with all their plants and animals.

So next time you happen to glance at a button mushroom in the grocery store, pause and reflect: you are gazing at one of the conductors of the symphony of life on land.

If it weren’t for fungi, we wouldn’t be here.

Immortal spores

Day after day, billions of invisible fungal spores rain down upon us. Each holds the DNA blueprint for a fungus, and it can faithfully preserve that DNA for astonishing periods of time.

Last year researchers from the Japan Agency for Marine-Earth Science and Technology grew a one-centimetre tall mushroom from spores recovered from a drill core, a long thin section of seabed material. Boring 2.5 km under the Pacific seabed, the bottom of the core contained 20-million-year-old sediments that carried the spores of an ancient land-based fungus. It appears most closely related to a species called Schizophyllum commune.

Medicinal fungi

Fungi have a titillating sex-life with up to 28,000 sexual identities to choose from, as well as sex-free procreation. That makes things tricky for mycologists, as Kathie Hodge from Cornell University found in 1994.

When she and her students went mushroom hunting in the woods of Ithaca in New York, they found a mysterious fungus sprouting from the corpse of a beetle grub. It was identified as C. subsessilis, a member of an insect-eating group of fungi known as Cordyceps. The surprise came when Hodge germinated the spores. They appeared to develop into a totally different species, the mould Tolypocladium. In fact, what Hodge discovered is that mouldy Tolypocladium is the asexual form of insect devouring C. subsessilis.

Tolypocladium is famous as the source of the immunosuppressant drug cyclosporine. Discovered 47 years ago, the drug single-handedly made organ transplants possible.

Thanks to Hodge’s woodland discovery, scientists are now fossicking in dead insects for the next generation of immunosuppressant drugs.

The third mode of life

Mushrooms may be conspicuous but they are the tip of the iceberg. The body of the fungus is a vast filamentous network of hyphae hidden below ground or inside the body of the plant or animal it is feasting on.

Biologists traditionally divide life into single-cell or multicellular organisms. Mark Fricker, a biologist at Oxford University, says this network represents “a third mode of life”.

Like a brain, these networks are adaptive. They respond to the environment, allowing fungi to deploy nutrients where they are most needed, explore resources, combat enemies or make urgent repairs. They are nature’s most efficient and resilient network.

Fricker is developing models to learn how these adaptive properties emerge and might be applied to solve the problems of man-made networks such as rail lines.

Radiation eaters?

These bioluminescent mushrooms may look otherworldly, but the most alien feature of fungi is that they can harvest radiation to grow. Scientists first got a hint of this after the Chernobyl nuclear plant meltdown in 1986.

In the clean up operation, they noticed dark-coloured fungi growing in the contaminated soils nearby. Their dark colour was due to melanin – the same pigment that colours human skin. Researchers thought melanin might be protecting the fungi against gamma radiation much as it protects us from UV rays.

But according to a 2007 study by Ekaterina Dadachova and Arturo Casadevall, then at Albert Einstein College of Medicine, fungi use melanin to harvest the energy of gamma rays. In the lab, gamma rays spurred the growth of a species called Cryptococcus neoformans. But only if its melanin-producing gene was intact.

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If you enjoyed this, then be sure to watch The Kingdom – How fungi made our world. You can watch the full documentary for free here.

Keep an eye out for more amazing science films and documentaries in SCINEMA 2022.

Don’t forget, submissions close 31 January!