LESSON 9: Introduction to Fungi PDF

LESSON 9 Introduction to fungi: Structure and morphology of fungi. Classification/ Fungal diseases COURSE MATERIALS: Kingdom Fungi consist of mostly multicellular eukaryotic organisms that are chemoheterotrophs (obtain energy by ingesting organic molecules like glucose), which ma...

LESSON 9 Introduction to fungi: Structure and morphology of fungi. Classification/ Fungal diseases COURSE MATERIALS: Kingdom Fungi consist of mostly multicellular eukaryotic organisms that are chemoheterotrophs (obtain energy by ingesting organic molecules like glucose), which make them different from plants that are photoautotrophs. This kingdom includes some of the most important organisms, both in terms of their ecological and economic roles. By breaking down dead organic materials, they continue the cycle of nutrients through ecosystems. Other fungi provide numerous drugs, such as penicillin, and other antibiotics, food like mushrooms, truffles and morels, and the bubbles in bread, champagne, and beer. They are found in just about any habitat but most live on land, mainly in soil or on dead plant matter rather than in sea of freshwater. Fungi also causes a number of plant and animal diseases. In humans, ringworms, athlete’s foot, and several more serious diseases are caused by fungi. Because fungi are more chemically and genetically similar to animals than organisms, this makes fungal diseases very difficult to treat. Some parasites of plants causing diseases include rust, smuts and leaf, root, and stem rots, and may cause severe damage to crops. However, a number of fungi, in particular the yeast, are important “model organisms” for studying problems in genetics and molecular biology. General Biology of the Fungi Morphology Fungi ranges in form and size from unicellular yeast to multicellular mushrooms and puffballs. Yeasts are unicellular, do not have flagella and reproduce asexually by budding or transverse fission or sexually by spore formation. Multicellular forms such as molds have long, branched, thread-like filaments called hyphae, which aggregate together to form a tangled mycelium. In some fungi the hyphae have cross walls or septa (septum) separating cells, which may nevertheless be joined by one or more pores, which permit cytoplasmic streaming, a form of internal transport. Many fungi are dimorphic that is, they exists in two distinct forms. Some fungi that cause human infections can change from the yeast form in the human to mycelial form in the environment in response to changes in nutrients, and environmental factors such as concentration of CO2 and temperature. This change in body form is known as the YM shift; in fungi associated with plants, the shift often occurs the other way around, the mycelial form exists in the plant and the yeast form in the environment. One of the feature that caused taxonomists finally removed fungi from the plant kingdom was the distinctive chemical nature of the fungal cell wall. Whereas the plant and algal cells have cell walls composed of cellulose, the cell wall of fungi is made up principally of chitin, a strong but flexible polysaccharide that is also found in the exoskeleton of insects. Nutrition Most fungi are saprobic, obtaining nutrition on dead and decaying organic matter, which they grow over and through, frequently secreting enzymes extracellularly to breakdown complex molecules to simpler form that can be absorbed by the hyphae. Most fungi are able to synthesize their own amino acids and proteins from carbohydrates and simple nitrogenous compounds. Although fungi are unable to move, they can swiftly colonize new territory as a result of the rapid rate at which their hyphae grow. All energy is concentrated on adding length rather than thickness; this growth pattern leads to an increase in surface area and is an adaptation to an absorptive way of life. Carbohydrates are stored mainly in the form of glycogen (c.f. starch in higher plants, green algae). Metabolism is generally aerobic, but some yeasts can function as facultative anaerobes. Reproduction There is a good deal of variety among the patterns of reproduction among the fungi, all share in common the feature of reproducing by spores; these are non-motile reproductive cells that rely on being carried by animals or the wind for their dispersal. The hyphae that bear the spores usually projects up into the air, aiding their dispersal. One of the main reasons that we have to practice aseptic techniques in the laboratory is that fungal spores are pretty well ubiquitous and will germinate and grow if they find a suitable growth medium. Spores of the common black bread mold, Rhizopus, have been found in the air over the North Pole, and hundreds of miles out to sea. In some fungi the aerial spore-bearing hyphae are developed into large complex structures called fruiting bodies. The most familiar example of a fruiting body is the mushroom. Many people think that the mushroom itself is the whole fungus, but it only represents a part of it; most is buried away out of sight below the surface of the soil or rotting material, a network of nearly invisible hyphae. Classification of the Fungi The Fungi are arranged into four major phyla on the basis of differences in their sexual reproduction. These are: 1. Zygomycota (zygomycetes) are mainly saprobic with coenocytic hyphae and haploid nuclei. They use sporangiospores for sexual reproduction. The group name comes from zygospores that they use for sexual reproduction, which have hard walls formed from fusion of reproductive cells from two individuals. Zygomycetes are important for food science and as crop pathogens. One example is Rhizophus stolonifera, an important bread mold that also causes rice seedling brightness. Mucor is a genus of fungi that can potentially cause necrotizing infections in humans, although most species are intolerant to temperatures found in mammalian bodies. Microscopic examination of the lungs. The hyphae of Zygomycota were frequently observed around and within the blood vessels causing obstruction and thromboembolization of blood vessels. Non-septate, irregularly branched hyphae of Zygomycota observed used a high-power field are shown in (C and D). The specimens were stained with hematoxylin and eosin stains in (A and C), while those in (B and D) were stained with Grocott’s methenamine silver stain. Notes: Magnification: (A and B), ×20; (C and D), ×100. https://www.researchgate.net/figure/Microscopic-examination-of-the-lungs-The-hyphae- ofZygomycota-were-frequently-observed_fig3_250925410 2. Ascomycota – include fungi that are used as food (mushrooms, morels, and truffles), other that are common causes of food spoilage (bread molds and plant pathogens), and still others are human pathogens. Ascomycota may have septate hyphae and cup-shaped fruiting bodies called ascocarps. Some genera of Ascomycota produce ascospores as well as spores called conidia, but sexual phases have not been discovered or described for others. Some produce an ascus containing ascospores within an ascocarp. Examples of Ascomycota include several bread molds and minor pathogens, as well as species capable of causing more serious mycoses. Species in the genus Aspergillus are important causes of allergy and infection and are useful in research and in the production of certain alcoholic beverages such as Japanese’s sake. The fungus Aspergillus flavus, a contaminant of nuts and stored grains, produces an aflatoxin that is both a toxin and the most potent known natural carcinogen. Neurospora crassa is of particular use in genetics research because the spores produce by meiosis are kept inside the ascus in a row that reflects the cell division that produces them, giving a direct view of segregation and assortment of genes. Penecillium notatum produces antibiotic penicillin. Examples of Ascomycota diversity. (A) Apothecia (yellow) of Orbilia, Orbiliomycetes (J. H. Petersen/MycoKey). (B) Apothecia of Aleuria, Pezizomycetes (J. H. Petertsen/MycoKey). (C) Thallus of Ophioparma with apothecia, Lecanoromycetes (B. McCune, Oregon State University). (D) Thallus of Lichinella, Lichinomycetes (B. McCune, Oregon State University). (E) Bitunicate asci of Thaxteriella, Dothideomycetes (S. Huhndorf, Field Museum). (F) Thallus of Arthonia with apothecia, Arthoniomycetes (B. McCune, Oregon State University). (G) Thallus of Prolixandromyces, Laboulbeniomycetes (A. Weir, SUNY-ESF). (H) Perithecia of Neurospora, Sordariomycetes (N. B. Raju, Stanford University). (I) Earth-tongue apothecia of Cudonia, Leotiomycetes (Z. Wang, Iowa State University). (J) Cleistothecia of Eupenicillium, Eurotiomycetes (D. Geiser, Penn State University). (K) Operculate ascus of Peziza (J. H. Petersen/MycoKey). (L) Ascostroma of Venturia, Dothideomycetes (T. Volk, University of Wisconsin at La Crosse). (M) Unitunicate asci Neurospora (N. B. Raju, Stanford University). (N) Prototunicate ascus of Eurotium (D. Geiser, Penn State University). https://www.researchgate.net/figure/Examples-of-Ascomycota-diversity-A-Apothecia- yellow-of-Orbilia-OrbiliomycetesJ_fig5_319869622 3. Basidiomycota – are fungi that have basidia (club-shaped structures) that produce basidiospores (spores produced through budding) within fruiting bodies called basidiocarps. They are important as decomposers and as food. This group includes rusts, stinkhorns, puffballs, and mushrooms. Several species are of particular importance. Cryptococcus neoformans, a fungus commonly found as a yeast in the environment, can cause serious lung infections when inhaled by individuals with weakened immune systems. The edible meadow mushroom, Agaricus campestris, is a basidiomycete, as is the poisonous mushroom Amanita phalloides, known as the death cap. The deadly toxins produced by A. phalloides have been used to study transcription. Examples of Basidiomycota diversity. Pucciniomycotina: (a) uredinia of Puccinia iridis; (b) fruiting body of Phleogena faginea; (c) aecia of Coleosporium; (d) yeast state of Symmetrospora oryzicola. Ustilaginomycotina: (e) smut galls of Ustilago maydis; (f) gall of Exobasidium; (g) culture of Moniliella sp. Agaricomycotina: (h) culture of Wallemia; (i) stinkhorn fruiting body of Phallus (photo by Nu Nguyen). (j) coral fruiting body of Clavaria; (k) crust fruiting body of Amylostereum; (l) club fruiting body of Clavariadelphis; (m) polypore, conk fruiting body of Pycnoporus; (n) gilled mushroom fruiting body of Russula; (o) pored mushroom fruiting body of Boletus; (p) puffball fruiting body of Lycoperdon. https://www.researchgate.net/figure/Examples-of-Basidiomycota-diversity-Pucciniomycotina-a-uredinia-of- Pucciniairidis_fig3_319869622 4. Microsporidia – are unicellular fungi that are obligate intracellular parasites. They lack mitochondria, peroxisomes, and centrioles, but their spores release a unique polar tubule that pierces the host cell membrane to allow the fungus to gain entry into the cell. A number of microsporidia are human pathogens, and infections with microsporidia are called microsporidiosis. One pathogenic species is Enterocystozoan bieneusi, which can cuase symptoms such as diarrhea, cholecystitis (inflammation of the gall bladder), and in cases, respiratory illness. Photomicrograph showing microsporidia (arrows) in stool stained with modified acid-fast trichrome https://www.researchgate.net/figure/Photomicrograph-showing-microsporidia-arrows-in-stool-stained-with- modifiedacid-fast_fig1_257908572 Fungal Diseases in Man Common fungal infections include: 1. Athlete’s foot (Tinea Pedis) is a fungal infection of the feet with itching, scaling and redness. It can be caused by a number of different fungi including Trichophyton, Epidermophyton, and Microsporum. 2. Ringworm (Tinea Corpis) it mostly appears anywhere in the body I the form of red or silver rash. It is usually ring-shaped and is most commonly caused by the fungus Trichophyton rubrum. 3. Tinea capitis is a ringworm that affects the scalp. 4. Onychomycosis is a fungal infection or the toenails and fingernails that can involve any component of the nail, including bed and plate. It can cause pain, discomfort and disfigurement. Onychomycosis is caused by fungal organisms, the most common dermatophyte. Yeast and molds also cause nail infection. 5. Tinea versicolor or Pityriasis versicolor is a common condition that causes small patches of skin to become scaly and discolored. They can be darker or lighter than the surrounding skin, or even red or pink. 6. Cutaneous Candidiasis can include any skin region of the body, however, for the most part, happens in warm moist, creased areas such as the armpits and groin. Candida is the most well-known reason for nappy rash in babies. Candida is likewise normal in individuals who are obese or have diabetes. Anti-infection agents, steroids treatment and chemotherapy increase the danger of cutaneous Candidiasis. Fungal diseases in Plants 1. White blister/ White rust) Albugo candida White blisters and swellings in leaves and heads of affected plants. Blisters consist of masses of white dust-like spores. Affects Brassicas, including Asian leafy brassicas. 2. Downy mildews (individual species damage particular crop families). Wide host range including onions, peas, lettuce, celery, spinach, kale, herbs, cucurbits, brassicas, Asian leafy brassicas. Symptoms usually begin with yellowish leaf spots which then turn brown. Downy growth appears on the underside of the leaves. 3. Powdery mildews (some species are restricted to particular crops or crop families). Small, white, powdery patches on most above-ground surfaces, usually observed first on undersides of leaves but eventually cover both surfaces, affected leaves become yellow, then brown and papery and die. Wide host range and very common, especially in greenhouse crops: cucumber, melons, pumpkin, zucchini, parsnip, beetroot, potato, herbs, peas, bitter melon, tomato, capsicum, Brussels sprouts, cabbage, swedes 4. Clubroot (Plasmodiophora brassicae) Affects Brassicas, including Asian leafy brassicas. Symptoms include large malformed clubbed roots which prevent the uptake of water and nutrients, reducing the potential yield of the crop. Plants are yellow and stunted and may wilt in hotter parts of the day. 5. Pythium species affects many vegetable crops including cucurbits, brassicas and lettuce. May kill seedlings which die before they emerge or soon after emergence, plant collapse. 6. Rusts (several species, e.g. Puccinia sorghi –sweet corn; Uromyces appendiculatus – beans; Puccinia allii – spring onions). It affects sweet corn, beans, onions, beets, and celery. Symptoms include small red or reddish-brown pustules that form on the underside of the leaves and sometimes on the pods as well. Dusty reddish- brown spores released from pustules. 7. Tuber disease (Various species). It affects potato and sweet potato. Potato tubers may be infected with superficial skin diseases, such as powdery sabs, and Rhizoctonia. Sweet potatoes may be infected by scurf. READINGS: Fungal infections you need to know about. Retrieved from: https://medicalwale.com/related_article/fitness/493/fungal-infections-you-need-to-know-about Fungal diseases in vegetable crops. Retrieved from: https://ausveg.com.au/biosecurity- agrichemical/crop-protection/overview-pests- diseasesdisorders/fungaldiseases/#:~:text=Some%20fungal%20diseases%20occur%20on,%3B %20Scle rotinia%20rots%3B%20Sclerotium%20rots. ACTIVITY/ASSESSMENT NAME:_______________________________________DATE: _________________ Activity: Factors affecting Mold Growth Materials: Slice of bread cut into 4 4 small sterile/clean transparent jars with cover. (Plastic cups with cover will do as long they are clean) Ballpen / permanent marker Scotch tape Water Medicine dropper or teaspoon Hand lens / magnifier or cellphone with camera. (To take pictures and zoom to enlarge the image.) Procedure: 1. Place a slice of bread in each jar. 2. Put a few drops of water in each slice of bread. 3. Cover tightly each jar, secure with scotch tape, and Label Set up A, B, C, and D and the date you prepared the set up. 4. Place each jar in different places in the house undisturbed for 5-7 days. Set up A. inside a cabinet in the kitchen or under the sink Set up B. inside the bathroom Set up C. Near a window. Set up D. Laundry area or garden or other place where it can be left undisturbed for 5 to 7 days 5. After one week observe each slice of bread for the presence of molds. NOTE: Never remove the cover of the jar (observe the set up without opening the jar). And dispose of the set ups in a secured trash bin after the activity. 6. Copy the table below for your observation. Observation: Set Location Conditions in the location (temp, Presence of mold (none, few, Up moisture, lighting, etc.) moderate, a lot) Color/s of molds A B C D Questions: 1. What was the locations that you found potential for mold growth? In what location/s you found least growth of molds? Why? 2. Did you find different molds growing on the slice of bread? How ddi you know? Where do you think these molds came from? 3. Why is it dangerous to open the containers once mold begins to grow? 4. What other items do you see growth of molds? Why? 5. What are the factors affecting the growth of mold? Conclusion: