Fungi
Do you fancy a sandwich? Can you make your own? If you can, you will know that the first things you need are two slices of bread. When you go to the bread bin you may find a new loaf sealed in a bag that is ready for opening. As you open the bag you let in air and take out two slices. They are wholesome and fresh and away you go to find some butter, tomatoes, prawns or whatever else you can find to make your sandwich. Over the next day, you may use the loaf for more sandwiches and perhaps toast. If you leave the loaf for a couple of days longer, you may find that something else has started to feed on the next slice you take out. It has grown as it has fed and given the bread a fuzzy coat. The bread has gone mouldy.

You may have started the first stage towards the bread going mouldy when you opened the bag. In the air around you are thousands of spores. Some of them are from bacteria and some are from fungi. There are even spores from mosses. When you took out your slices of bread, air swirled into the bag carrying a mould spore. It was swept onto a slice remaining near the bottom of the bag and settled there.

The air also contains water vapour. Over the days that the loaf was in the bread bin, the amount of water vapour in the air was quite high. When a hot tap was run at the kitchen sink, some water vapour escaped into the air. When pans were boiling on the cooker, water vapour escaped into the air. In time some of this water vapour found its way onto the bread and condensed. This water made the bread just moist enough for the spore to break open.

Inside a fungal spore is a tiny piece of fungus. When the spore breaks open, this tiny piece grows out to find food. The fungus from this spore grows down into the bread and begins to feed. Fungi feed like animals but they do not have teeth and digestive systems. They make a juice, which contains chemicals called enzymes. This juice is similar to the digestive juices we produce in our body. The juice made by the fungus leaves its body and flows into the food around it. The enzymes set to work breaking down the food so that it dissolves. The fungus can only feed on food that has dissolved. When the food has dissolved, the fungus draws it in to its body and uses it for growth.

Fungi need some warmth to grow well. In the kitchen the temperature is high enough to help the fungus start producing new material for growth. A fungus grows by making threads thinner than a human hair. The threads grow through the food and form a mat. When the fungus has produced enough threads, it reproduces or breeds. Some fungi, like mushrooms and toadstools, produce large structures like umbrellas above ground. They are called fruiting bodies. We just refer to them as mushrooms or toadstools. The fruiting body is divided into two parts. These are the stalk and the cap. When the fungus is ready to breed, the cap grows and opens out. On the underside of the cap, black structures called gills are exposed and thousands of spores are released from them.

A mould does not produce a fruiting body like a mushroom but it does produce spores. When a mould is ready to breed it sends up threads out of the bread. A black swelling develops on the end of the thread. Inside this swelling spores develop. When they are fully formed the swelling breaks open and the spores are released into the air. They are so small and light that they are carried away in the air currents. Many land in unsuitable places and never grow into new fungi but some are luckier. The next slice of bread you pick up may already have been visited by a lucky spore and have a mould growing on it.

Are fungi plants or animals?
They are neither. Fungi used to be placed in the plant group because the feeding threads looked like roots and the stalks of mushrooms and toadstools looked like stems. They also produced spores like mosses, ferns and horsetails. However plants contain a green substance which they use to make food from sunlight. They use air, water and minerals from the soil in the food-making process. Fungi do not have the green substance and cannot make food. They must obtain their food by digesting it like animals. Fungi do not have other features of animals. For example they cannot move around and do not have parts such as a heart or brain. Fungi have enough unusual features to place them in a group on their own.

Why are fungi called microbes when some of them, like mushrooms, are quite large?
The members of the fungi group vary greatly in size. Some, like the yeasts, are so small that you need a microscope to see them, while mushrooms, toadstools and bracket fungi, which grows out of the trunk of a living tree, are clearly large enough to see easily. It is only the small members of the fungi group which are called microbes. They are the moulds, rusts, mildews and yeasts. The spores of all fungi are so small that they can only be seen with a microscope.

What colour are spores?
The spores of many fungi are grey but some may be red while others such as the penicillin fungus are blue.

Are there any other common microbe fungi besides mould on bread?
Yes. There are mildews that attack germinating seeds. If you sow some seeds in damp conditions spores of mildew may break out on them and the seedlings will be attacked by the feeding threads. As the mildew grows over the seedlings they die. We say that this process is called damping off. To avoid it you must not over water seeds when you plant them.

Do fungi use only the air to disperse their spores?
Most do but there are two unusual ways of releasing spores. A fungus which grows on horse manure produces a case of spores on the end of a thread. Just below the spore case, the thread swells up with liquid. Eventually it suddenly explodes and shoots the spore case away from the manure. The reason for this is that the spores need to be eaten by a horse so they can pass out of its body with the manure. A horse will not graze grass close to any manure so the spores have to be shot a good distance away to increase the chances of their being eaten. A puffball is produced by a few fungi. This may be the size of a tennis ball or even larger and is full of millions of spores. It has a soft flexible skin, which breaks open when the spores are ready to be dispersed. When the wind blows on the puffball or raindrops fall on it, they push in on the skin and make it puff out spores.

Can microbe fungi live in water?
Yes, some kinds do. These are water moulds. The threads form a furry surface on dead fish and other water animals. These fungi produce spores which have long hairs, which they move like whips. The movement helps to spread out the spores in the water.

Do fungi help to break down dead plants and animals?
Yes, they do. Bacteria are the main decomposers but fungi also play their part.

Do some animals farm moulds?
Yes, they do. The leaf cutter ant stores leaves inside its nest and lets a mould grow on it. Although the ant sometimes eats the mould it is not really grown for food. As the mould grows it generates a little heat which is used to warm the spaces inside the nest.