Fungi Microbiology PDF

FUNGI Fungi (singular, fungus)  classified as a kingdom – separate from plants, animals, and bacteria  commonly known as molds and yeasts and have some similarities with bacteria  Non-motile; filamentous (filament – interconnected cells)  plant-like eukaryotic spore-bearing proti...

FUNGI Fungi (singular, fungus)  classified as a kingdom – separate from plants, animals, and bacteria  commonly known as molds and yeasts and have some similarities with bacteria  Non-motile; filamentous (filament – interconnected cells)  plant-like eukaryotic spore-bearing protists which develop branching interlacing filaments called mycelia and lack chlorophyll  Generally heterotrophic; they live in their food and absorb nutrients from their food  perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange o heterotrophic bacteria – other decomposers  Cell walls have polysaccharide compound called chitin o Insects – other organisms that have chitin in their cells  generally reproduce both sexually and asexually  life cycle involves spore production o spores – capable of giving rise to other organisms 1   direct source of food, such as mushrooms and truffles  various industrial functions  inconspicuous because of the small size but may noticeable when fruiting, either as mushrooms or molds  study of fungi is called mycology Fungi include:  Yeasts – unicellular organisms  Molds – multicellular filamentous organisms such as mildews, rusts and smuts  Fleshy fungi are multicellular filamentous organisms that produce a thick (fleshy) reproductive body, e.g. mushrooms, puffballs and coral fungi Common Appearance of multicellular fungi  Velvety blue and green growth on rotting oranges and lemon and stale cheeses  Whitish-gray furry outgrowths on bread and jam  Mushroom in the fields Characteristics of Fungi  Fungi are heterotrophic organisms which require organic compounds for nutrition  They decompose complex plant and animal remains, breaking them into simpler chemical substances that are returned to the soil thereby increasing its fertility. However, they also decompose timber, textiles, food and other materials  Fungi can be both saprophytic and parasitic  Saprophytic fungi are important in industrial fermentation - Brewing of beer, - Making wine, breaking down of sugar to form alcohol - Production of antibiotics such as penicillin - Leavening of dough, production of soy sauce - Ripening of some cheeses, and give characteristic flavor to certain popular types of cheese o Before the advent of refrigeration, preserving of milk products was done by inoculating milk with fungal spores which develops into mycelia; this prevents the growth of other microorganisms, e.g. Staphylococcus and Clostridium, which will spoil or rot the milk now in the form of cheese o Cheese making generally consists of three basic steps. The first step is precipitation of the milk into curds, the second is concentration of the curds and removal of the whey by pressing and draining, and the third is aging or “ripening”. The purpose of ripening is to allow bacteria and other microbes to act on the curds and transform them into the final product. It’s during this last step that an ordinary cheese can become a blue cheese, using a blue-green mold such as Penicillium roqueforti. This mold grows within the cheese and breaks down complex organic molecules into simpler ones, smoothing out the fibrous structure of the cheese and providing the sharp flavor and smell associated with blue cheeses. - various enzymes produced by fungi are used industrially and in detergents o submerged citric acid fermentation by Aspergillus niger using blackstrap molasses as the basal fermentation media o brown rot fungi Gloeophyllum trabeum produce oxalic acid in liquid as well as in semisolid cultures during decay of pine holocellulose 2  as biological pesticides to control weeds, plant diseases and insect pests  Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to plants, animals including humans  Parasitic fungi cause disease in plants, humans and other animals. Disease in humans are called mycotic infections o Aflatoxins – are naturally occurring mycotoxins that are produced by many species of Aspergillus, a fungus, the most notable ones being Aspergillus flavus and Aspergillus parasiticus. Aflatoxins are toxic and among the most carcinogenic substances known. After entering the body, aflatoxins may be metabolized by the liver to a reactive epoxide. Crops that are frequently affected include cereals (maize, sorghum, pearl millet, rice, wheat), oilseeds (peanut, soybean, sunflower, cotton), spices (chilli peppers, black pepper, coriander, turmeric, ginger), and tree nuts (almond, pistachio, walnut, coconut, brazil nut). o Some mushrooms are poisonous when ingested, e.g. Amanita muscaria  Can cause food spoilage (a) (b) (c) (a) Watery soft rot in apple caused by Sclerotinia sclerotiorum, (b) Storage rot in strawberry caused by Botrytis cinerea (c) Blue mould rot in tomato caused by Penicilliumi spp  Fungi can withstand certain extreme environmental conditions than most other microorganisms. For example, yeasts and molds can grow in a substrate or medium containing concentrations of sugars that inhibit most bacteria. This is why jams and jellies may be spoiled by molds but not by bacteria. Yeasts and molds generally can tolerate most acidic conditions that most other microbe. Also spoil food preserved in salts and vinegar and in refrigerators because they grow slowly in refrigerators.  Some yeasts are facultative – they can grow under both aerobic and anaerobic conditions  Fungi are capable of using wide variety of materials for nutrition but basically heterotrophic (need for organic materials). They disfigure walls and floors of buildings and cause dry rot in lumber.  Develop on soiled damp towels, clothing in the laundry bag, old shoes stored away in closets, books on library shelves.  Optimum temperature for growth: 23 – 30oC (saprophytic), 30 – 37OC (pathogenic); some 0oC 3 Morphological Features of Fungi  Thallus (plural, thalli) or body of a fungus may consist of a single cell as in the yeasts, more typically the thallus consists of filaments which are commonly branched. Yeast mycelium  Some fungi are dimorphic, that is, they exist in two forms: yeast-like and filamentous  Yeast cells are generally larger than most bacteria. Yeasts have no flagella or other organelles of locomotion Yeast (long cylindrical), bacteria (small rod-shaped)  The thallus of a mold consists essentially of two parts, the mycelium and the spores (resistant, resting or dormant cells)  Mycelium is a complex of several filaments called hyphae (singular hypha). New hyphae generally arise from a spore which on germinations puts out germ tube or tubes. This germ tube elongates and branch to form hyphae. 4   The growth of hyphae is ear the tip. Hyphae occur in three forms o Non-septate: no septa o Septate with unincleated cells o Septate with multinucleated cells. Each cell has more than one nucleus in each compartment Reproduction of Fungi 1. Asexual Reproduction  Does not involve the union of nuclei or sex cells  Asexual spores: produced in large numbers in order to disseminate the species  Somatic or vegetative reproduction Types of Asexual Spores a. Zoospores - motile asexual spore that uses a flagellum for locomotion b. Sporangiospores – single-celled spores formed within sacs c. Oidia – formed by disjointing of hyphal cells d. Chlamydospores – thick-walled, single-celled spores which are highly resistant to adverse conditions; formed from cells of vegetative hyphae e. Conidiospores – formed at the tip or side of a hyphae f. Blastospores – spores formed by budding 5 2. Sexual Reproduction  Carried out by the fusion of the compatible nuclei of two parent cells Types of Sexual Spores a. Ascospores – single-celled spores produced in the sac called ascus b. Basidiospores – single-celled spores borne on a club-shaped structure called basidium c. Zygospores – large, thick-walled spores formed when the tips of two compatible hyphae or certain fungi fuse together 6 Classification of Fungi 1. Myxomycetes – slime fungi 2. Zygomycetes – fungi characterized by the formation of sexual spores (zygospores), and vegetative mycelium that lack septa 3. Ascomycetes – sac fungi; mycelium is septate 4. Basidiomycetes – rusts, smuts and mushrooms; sexual spores borne on special club-like stalks 5. Deuteromycetes or Fungi imperfecti – miscellaneous; asexual spores of various types; mycelium is septate; we do not know of their complete life cycles or how exactly they reproduce, only that it is asexual. Deuteromycota have long, threadlike tissues that form the body of sac and club fungi. Their branching tubes have asexual spores, called conidiophores, in them. Most asexual spores in other fungi are produced by sporangium, but these are not. Pathogenic fungi belong to this group 7 Fermentation  Yeast is used in winemaking, where it converts the sugars present in grape juice (must) into ethanol. Yeast is normally already present on grape skins (the white powder called “the bloom”). Fermentation can be done with this endogenous "wild yeast”  S. cerevisiae, is used in baking as a leavening agent, where it converts the fermentable sugars present in dough into the gas carbon dioxide. This causes the dough to expand or rise as gas forms pockets or bubbles. When the dough is baked, the yeast dies and the air pockets "set", giving the baked product a soft and spongy texture Bioremediation  Some yeast can find potential application in the field of bioremediation. One such yeast, Yarrowia lipolytica, is known to degrade palm oil mill effluent, TNT (an explosive material), and other hydrocarbons, such as alkanes, fatty acids, fats and oils. It can also tolerate high concentrations of salt and heavy metals, and is being investigated for its potential as a heavy metal biosorbe Diseases Caused by Fungi: Mycosis or Mycotic infection 1. Superficial 2. Subcutaneous 3. Deep (systemic) 4. Opportunistic 1. Superficial Mycoses – caused by fungi that invade ony superficial tissues (skin, hair and nails) but do not invade deeper tissues Examples:  Tinea Pedis (Athlete’s foot) – toe webs are infected with Trichophyton species. Initially, there is itching between the toes and the development of small vesicles that rupture and discharge thick fluid. This skin of toe webs peels and are prone to secondary bacterial infection  Tinea Unguium (Onychomycosis) – nail infection, follows prolong tinea Pedis. Nail becomes yellow, brittle, thickened or crumbling  Tina Corporis, Tinea Cruris (Ringworm) – occurs in non-hairy skin of the body that gives rise to annular lesions of ringworm, with a clearing, scaly center surrounded by red borders  Tinea Capitis (Ringworm of the scalp) – Infection of the hair takes place just above the hair-root. Some invade the hair shaft making it so fragile that it breaks off within or at the surface of the hair follicle leaving short stubs in balding, usually circular patch  Tinea barbae – involve bearded region of humans 2. Subcutaneous Mycoses – the fungi causing the subcutaneous mycoses grow in soil or on decaying vegetation. They must be introduced into the subcutaneous in order to produce disease. 3. Systemic Mycoses – are caused by soil fungi. Infection is acquired by inhalation and most infections do not show symptoms 8 4. Opportunistic Mycoses – fungi that usually do not induce disease may do so in persons who have altered host defense mechanism. Such opportunists may infect any or all organs of the body.  Candidiasis – caused by Candida albicans, a member of normal flora of the mucous membranes in the respiratory, gastro intestinal, and female genital tracts; clinical symptoms: lesions in the mouth, intense itching, irritation, and discharge in female genitalia  Cryptococcus neoformans - yeast like fungus free living in the soil may cause meningitis. The fungus also produces acne-like skin lesions, subcutaneous tumor-like masses and pulmonary disease. Usual sources of infection are droppings or excreta of pigeons and chickens 9