Fungi D What are fungi? Example: Truffles Structure and reproduction of fungi Fairy rings Spores Anaerobic respiration and fermentation

What are fungi? There are over 40 000 varieties of fungi known. Many are useful in recycling nutrients in dead plants or animals. Fungi can be single-cellular (eg yeasts) or multicellular (eg mushrooms). Unlike other microbes, some fungi are visible to the naked eye. All fungi grow best in warm, moist conditions. For example, bread is more likely to go mouldy in summer than in winter, especially if the humidity is high or it is left in a plastic bag.

Each species of fungi will grow only on its own food source Each species of fungi will grow only on its own food source. Bread mould won’t make cheese or an orange go mouldy. There are thousands of different types of mushrooms that only grow on different species of trees. Example: Truffles Truffles are produced by a fungus that lives underground on oak trees. They are used to flavour food and are worth about $3000 per kg! Although most truffles are grown in France, a few people are starting to grow and sell truffles in New Zealand.

Most fungi are saprophytes: they live on or digest dead material Most fungi are saprophytes: they live on or digest dead material. For example: moulds on fruit yeast in flour for making bread yeast on grapes used to make wine

Some fungi are parasites: they live on, or digest, living things Some fungi are parasites: they live on, or digest, living things. For example rusts on plants mushrooms on trees athlete’s foot on humans.

What are fungi? Fungi cannot make their own food but must grow on their food source. All fungi like warm, moist conditions. Some fungi are unicellular, eg yeast (used to make bread and beer), while others are multicellular, eg mushrooms. Most fungi are saprophytes, meaning they live on and digest dead material, eg wood and bread. Other fungi are parasites, meaning they live on and digest living things, eg rusts on plants and athlete’s foot in humans. 6D 1 Making bread 6D 2 Pros and cons

Structure and reproduction of fungi The main ‘body’ of a multicellular fungus consists of fine threads, called hyphae, that burrow through the surface layer of the food source, absorbing nutrients through extra-cellular digestion. The tangled ‘mat’ of hyphae is known as a mycelium. Periodically the fungus sends up reproducing hyphae that support sporangia. When each sporangium bursts, it releases tiny spores that are carried by the air.

Fairy rings Mushrooms growing for many years in the same field will form a ring that grows in diameter each year. The absorbing hyphae are forced to spread ever outwards as the inner part of the ring becomes depleted of nutrients and is loaded with waste products. The mushrooms we eat are just the fruiting bodies of the fungus. Just as an apple tree will fruit again, so picking all the mushrooms in a field will not prevent more mushrooms popping up in a few weeks.

The structure of fungi Spores Tiny particles containing genetic material in a tough outer coat. Mycelium A tangled web or mat of hyphae. Sporangium A fruiting body containing spores. Extra-cellular digestion Method of feeding used by fungi. Hyphae Fine threads that spread through the surface layer of a food source. 6D 3 Fungi words

Spores Most fungal spores are generated from a single individual, therefore the reproduction is asexual. Spores contain the genetic material for a new organism in a tough coat that allows it to survive for many years. Spores are similar to seeds, but contain no food supply. The spore will only grow if it encounters the right food source plus sufficient warmth and moisture for growth. The air around us contains thousands of fungal spores for many different species of fungi, just waiting for the opportunity to grow.

Although most fungal reproduction is asexual, fungi can reproduce sexually, creating variation and new strains of fungi. The mechanism for sexual reproduction in fungi is beyond this course. Spores Spores contain the genetic material for growth of a new organism, protected by a tough coat. The spores can remain viable for many years. They will germinate when they encounter favourable conditions including the correct food source. Most spores are produced asexually, but under certain circumstances fungi reproduce sexually, allowing new strains of fungi to form. 6D 4 Fungal diseases

Anaerobic respiration and fermentation When we obtain energy from food such as glucose, the process is aerobic (with oxygen) respiration and the products are carbon dioxide and water. Some microbes, such as yeast, can carry out aerobic respiration on glucose when oxygen is present, but can also obtain energy from glucose through anaerobic (without oxygen) respiration. In that case the products are carbon dioxide and ethanol (alcohol). Bacteria respire anaerobically to turn the sugar in milk (lactose) into lactic acid when yoghurt is made. The special term fermentation is used to describe anaerobic respiration of carbohydrates to produce an alcohol or acid.

Yeast fermentation produces the ethanol for wine, beer, vodka and saki. Yeast fermentation also produces the carbon dioxide that makes bread rise (the alcohol evaporates during baking of the bread). Sauerkraut and kimchi are produced by bacteria that turn the sugars in cabbage into acid, helping to preserve the cabbage for many months. Silage is also a product of fermentation, preserving surplus grass for times when feed is scarce.

Anaerobic respiration and fermentation Aerobic respiration is respiration with oxygen: glucose + oxygen → carbon dioxide + water Anaerobic respiration is respiration without oxygen. Yeast can obtain energy from glucose anaerobically: glucose → carbon dioxide + ethanol Some bacteria produce lactic acid through anaerobic respiration. This happens in yoghurt. We use the special term fermentation to describe anaerobic respiration to produce an alcohol or acid. Fermentation of yeast makes the alcohol for wine or beer and the CO2 that makes bread rise. 6D 5 Fermentation trials 6D 6 A nice drop

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