By Kirsty Jackson (@kjjscience)
As a child I was drawn to fungi. I liked to eat them and I was fascinated by the way they seemed to pop up out of the grass. Like a lot of people I grew up thinking that fungi were a type of plant. After all they come out of the ground or trees, are a variety of different shapes and colours and are relatively inanimate. It wasn’t until my early teens, in my science classes, that I learned that fungi were a type of living thing separate from plants and animals. At university I discovered that fungi are actually closer in evolutionary history to animals than they are plants.
Fungi in fact have a biological kingdom all of their own. There are 7 phyla in the kingdom with the Ascomycota and Basidomycota being the largest. Ascomycetes include the yeast-types and the Basidomycetes contain the mushroom-type and most pathogenic fungi. Glomeromycota are all arbuscular mycorrhizal fungi. Microsporidia are unicellular parasites, Neocallimastigomycota are anaerobic fungi and Chytridiomycota are mostly aquatic fungi that produce spores that have flagella – similar to bacterial flagella. The evolutionary history of fungi is still under debate and techniques such as ribosomal sequencing are being used to figure it out . I shall mostly be talking about the Ascomycota and the Basidiomycota.
Fungi can reproduce sexually or asexually in the form of spores. The spores will germinate, much like a seed, with a special hyphae called a germ tube and a vegetative hyphae will grow from the germ tube. More than one germ tube can be produced from one spore. Hyphae are long tube-like cells that grow at the tip.
The nuclei replicate as in normal cells and are free to travel around the whole of the hyphae – in a biological phenomenon known as a syncytium (see video below).
As the hyphae grow, they branch and fuse with each other to form a net-like structure that covers the whole area surrounding the initial spore called a mycelium (see below). Mycelia can be seen clearly on any foodstuff that becomes mouldy.
Recently, it has been published that in the early growth stage after germination, two different asexual spores can also fuse using a third kind of specialised hyphae called a conidial anastomosis tube (see left). This could be to ensure a wider hyphal network and access to more nutrients .
As the hyphae become older the fungi will build walls within the tubes called septa which start out like an open door way in a corridor but eventually the door becomes shut.
The mushrooms and toadstools that can be seen sprouting out of the ground or trees (or even the walls of houses or in the corners of damp bathrooms) are known as fruiting bodies. The fruiting bodies are made up of thousands and thousands of hyphae all working together in the same manner as the cells in your body. You can think of them in the same way you think of a flower on a plant. From the gills or pores on the underside of the cap the spores are shed and the whole cycle starts again. The mushrooms (fruiting bodies) are often produced when the underground mycelium reaches a barrier or when they hit an internally defined time or distance from the initial centre. This is why mushrooms are often seen at the side of the road, along paths or walls. This also explains the phenomenon of fairy rings (see below); the mushrooms of the ring are usually all connected to the same network of underground hyphae and are produced at its extremity.
Fungi are a very important part of the ecosystem; they are one of the decomposers preventing the world from being a big pile of dead plants and animals and returning important nutrients back into the soils to re-enter the food chain. They help to maintain soil structure and can, in the case of mychorrhizae, help plants directly in nutrient acquisition. They are both a food directly and help to make other lovely edible items such as bread and beer (or not so lovely i.e. marmite). They are also involved in the industrial production of vitamins B2, D2, E and F. They can also survive nuclear radiation!
About the author: Kirsty Jackson is a fellow PhD student at the John Innes Centre, Norwich. She is studying rhizobial and mycorrhizal symbioses with legumes and loves all things fungi! When she isn’t in the lab she is involved with organising science outreach events. Follow her on twitter (@kjjscience)
Image credits – Most images by the author except:
- Pleurotus ostreatus mycelium on coffee grounds by Tobi Kellner distributed under a CC BY-SA 3.0 licence.
Fairy Ring by Aviddoghug (no restrictions on use).
1. James, T.Y., et al., Reconstructing the early evolution of Fungi using a six-gene phylogeny. Nature, 2006. 443(7113): p. 818-822.
2. Gabriela Roca, M., N.D. Read, and A.E. Wheals, Conidial anastomosis tubes in filamentous fungi. FEMS Microbiology Letters, 2005. 249(2): p. 191-198.
- “Watch out mate, aphids are about!” Plant-to-plant communication via mycorrhizal fungi (plantscientist.wordpress.com)