Fungi: Yeast and Moulds (Chapter 1.3) PDF

1.3 FUNGI :YEAST AND MOULDS 1 AT THE END OF THIS SUBTOPIC, YOU WILL BE ABLE TO: 1. List the basic characteristics of fungi. 2. Describe the characteristics of fungi in yeast, dimorphic and mould form. 3. Name and describe the reproduction method of yea...

1.3 FUNGI :YEAST AND MOULDS 1 AT THE END OF THIS SUBTOPIC, YOU WILL BE ABLE TO: 1. List the basic characteristics of fungi. 2. Describe the characteristics of fungi in yeast, dimorphic and mould form. 3. Name and describe the reproduction method of yeast (asexual process). 4. Name and describe the reproduction method of mould (asexual and sexual processes). 2  INTRODUCTION: FUNGI Fungi (plural form, singular: fungus)  Fungi are eukaryotic organisms, meaning they have a nucleus in their cells. They can live on dead matter (as saprophytes) or on living matter (as parasites). Fungi get their nutrients by absorbing them from the environment. They are heterotrophs, which means they cannot make their own food and must rely on other organic matter for energy. There are two main forms of fungi: moulds and yeasts. 3 4 YEAST 5  INTRODUCTION: YEAST  Yeasts are single-celled fungi (unicellular). They reproduce mostly by a process called budding, where a small part of the yeast cell grows and eventually separates to form a new cell Some yeasts also reproduce by fission (not binary fission)  They prefer to grow in moist environments with plenty of nutrients. Yeast cells 6 7 Yeasts are facultative anaerobes (can grow with or without oxygen. They get their energy through aerobic respiration as well as fermentation).  Common yeast: Saccharomyces cerevisiae, used in: baking industry: to expand, or raise, dough. brewing industry: to ferment the sugars of rice, wheat, barley, and corn to produce alcoholic beverages. 8 Yeast cells THE YEAST'S FUNCTION IN BAKING to ferment sugars present in the flour or added to the dough. This fermentation gives off carbon dioxide and ethanol. The carbon dioxide is trapped within tiny bubbles and results in the dough expanding, or rising. 9 MOULD 10  INTRODUCTION: MOULDS Moulds are multicellular form of fungi. They appear as thread-like structures called hyphae (plural, hypha if singular). Most are obligate aerobes (need oxygen to survive). Mould hypha structure 11  They grow on the surface and inside of materials like food and other organic matter. 12 The mass of hyphae is called mycelium, which can be seen as fuzzy patches or dusty little spots often found spreading over bread, cheese, books, and other things at home. Moulds can be harmful to health and cause food spoilage, but they also play important roles in nature. 13 Mycelium – a mass of hyphae 14 Some species of moulds produce mycotoxins, toxic compounds that can contaminate crops, food, and cause health risks to humans and animals. 15 aerial mycelium/ hyphae the portion that stick out above the surface of the medium produces asexual reproductive spores. vegetative mycelium/ hyphae The part that anchors (holds) the mould, penetrates the medium & absorbs nutrients 16 17  REPRODUCTION OF MOULDS Moulds can reproduce in two ways: Asexual reproduction: Mold produce spores by itself, without needing another mould, producing asexual spores. Types of asexual spores: conidiospores, sporangiospores, arthrospores. Sexual reproduction: Two compatible moulds produce spores together, producing sexual spores. Mold produce spores by itself, without needing another mould, producing asexual spores. Types of sexual spores: oospores, zygospores, ascospores, and basidiospores. 18 ASEXUAL SPORES 19 1. CONIDIOSPORES Spores borne externally on an aerial hypha Looks like dreadlocks 20 21 SCANNING ELECTRON MICROGRAPHS OF THE CONIDIOSPORES OF Penicillium sp. 22 ELECTRON MICROGRAPHS OF THE CONIDIOSPORES OF Aspergillus sp. 23 2. SPORANGIOSPORES Mold spores borne internally within a sac or sporangium on an aerial hypha (e.g. Rhizopus sp., Mucor sp.) Looks like afro 24 SPORANGIOSPORES OF Rhizopus sp. 25 3. ARTHROSPORES Fungal spores produced by fragmentation of hyphae (e.g. Geotrichum) 26 ARTHROSPORES OF Coccidioides immitis 27 arthrospores 28 SEXUAL SPORES 29  (1) OOSPORES A spore with thick wall, developed from a fertilized oosphere in some fungi *oosphere: unfertilized egg 30 (2) ZYGOSPORES  One thick spore between 2 parent hypha 31  ZYGOSPORE ILLUSTRATION 32 33 34 (3) ASCOSPORES 4 or 8 spores in a sac called ascus, at the end of one hyphae 35 A: THREE KINDS OF ASCI: CYLINDRICAL, CLAVATE, AND SPHERICAL 36 37 (4) BASIDIOSPORES  4 spores on the end of a basidium. 38 39 DIMORPHIC FUNGI fungi that can change between yeast phase and hyphal phase, depending on environmental conditions. 40  Candida albicans a dimorphic fungus that grows at 37°C. normal habitat - mucosal membranes of humans and other warm-blooded animals, where it grows as a yeast and causes little or no damage. however, the same strains that grow as harmless commensals can become pathogenic. Under certain circumstances, C. albicans can cause infections that range from the skin infections to life-threatening systemic infections. *Systemic = affecting the entire body. 41 42 Mucor indicus; a dimorphic, non-pathogenic fungus. Used to produce ethanol and several foods. 43