12 October 2014 is UK Fungus Day, held by the British Mycological Society to showcase the diversity and usefulness of fungi, and the benefits of mycology (the study of fungi). Many people equate fungi with mushrooms, but mushrooms are only the visible, above-ground part of certain types of fungi. The bulk of such a fungus’s volume is underground and consists of microscopic threads called hyphae, which can form huge, interconnected networks. This means that mushrooms some distance apart may well belong to the same fungal organism.
Like plants and animals, fungi belong to the domain Eukaryota, which contains all organisms whose cells contain a nucleus. Unlike other eukaryotes, however, the cell walls of fungi contain chitin, a chemical structure also found in the hard shells of many insects and crustaceans.
Fungi are found around the world, with some 100,000 species currently known to mycologists. However, it is estimated that several million different species exist worldwide, so there is plenty of scope for discovery. Fungal species can grow in the most inhospitable regions, including deserts, deep ocean seafloors, and severely irradiated ground; some can even survive the intense ultraviolet and cosmic radiation in outer space, as findings aboard the International Space Station have shown.
Until just a few decades ago, fungi were thought to be closely related to plants: they both grow in similar habitats and do not move, and many fungi have similar above-ground shapes as flowering plants. Since the advent of molecular methods, however, we know that plants and fungi became genetically separate about a billion years ago. In fact, fungi are more closely related to animals than to plants!
Furthermore, while plants use photosynthesis to generate energy from sunlight, fungi are heterotrophs. This means that they rely on carbon that other organisms – such as plants – have converted into organic matter. Fungi are therefore the main decomposers in most ecosystems, digesting dead organic matter such as leaves and wood. They are central to many food webs and to the global nitrogen and carbon cycles.
Fungi are not just essential in most of Earth’s ecosystems and in regulating the planet’s chemical cycles, they are also used by us in a great many processes. Soft drinks, for example, contain citric acid made by the fungus Aspergillus niger, while beer, wine and some spirits are based on the yeast Saccharomyces cerevisiae. Another fungus, Penicillium notatum, was the basis for the first ever antibiotic – Penicillin was discovered by Alexander Fleming just over 86 years ago.
Beyond the importance of fungi to nature and to ourselves, they are also remarkable organisms in their own right. For example, the world’s largest living being was recently found not to be a blue whale, but an enormous fungus in the US state of Oregon. It covers nearly 4 square miles, big enough to cover over 1,600 football fields. From its growth rate, scientists have deduced that it could be anywhere between 2,400 and 8,600 years old, which would also make this the world’s oldest living organism.
If you would like to find out more about mushrooms, listen to our podcast, Microbe Talk, from July. Our very own Dr Benjamin Thompson talks to Dr Bryn Dentinger, an expert on fungi at the Royal Botanic Gardens at Kew, London.
Here’s to another billion years of fungi making life on earth possible and contributing to its little luxuries!