Yeast, molds, mushrooms, mildews and theother fungi pervade our World. They work greatgood and terrible evil. Upon them, indeed,hangs the balance of life; for without theirpresence in the cycle of decay andregeneration, neither man nor/or any otherliving things could survive. -Lucy Kavaler.
The living world is divided into the five kingdoms of Planta, Animalia, Fungi, Protista and Monera. It is important to recognize that the fungi are not related to bacteria (Monera). Fungi are eukaryotica, heterotrophic, unicellular to filamentous, rigid cell walled, sporebearing, organisms that usually reproduce by both sexual and asexual means. Further they are insensitive to antibacterial antibiotics. Eukaryotic cells also exhibit mitosis. But not prokaryotic cells. Heterotrophic - that are either saprophytes (living on dead organic matter) or parasites (utilizing living tissue). Like plants, fungi have rigid cell walls and are therefore non- motile, a feature which separates them from animals.
FUNGI (Mycology) Diverse group of heterotrophs. Many are ecologically important saprophytes (consume dead and decaying matter) Others are parasites. Most are multicellular, but yeasts are unicellular. Most are aerobes or facultative anaerobes. Cell walls are made up of chitin & glycan & a cell membrane ergosterol. Over 80,000 to 100,000 fungal species identified. 1.5 million may exist. Only about 50 - 100 are human or animal pathogens. Most human fungal infections are nosocomial and/or occur in immunocompromised individuals (opportunistic infections). Fungal diseases in plants cause over 1 billion dollars/year in losses.
Harmful fungi: Human, Animal and Plant Diseases. 25-50% of harvested fruits and vegetables are damaged by fungi. Fungal infections of plants are commonly called rots, rusts, blights, wilts, and smuts. eg Phytophthora infestans: Beneficial fungi: Decomposers- separates carbon, nitrogen, phosphorous & other critical constituents. Industrial process Making bread , wine and beer. In preparation of some cheese, soy sauces & sufu. In production of many organic acids ( Citric, galic acids etc.) In Production of Alcohol/ethanol In antibiotics (Penicillin, griseofulvin) In certain drugs (Ergometine, cortisone) In Immunosuppressive drug cyclosporine Biopesticides As a Research tools in study of the fundamental biological process. As model system Candida oleophila: Prevents fungal growth on harvested fruits. Saccharomyces cerevisiae: Used to make bread and wine. Genetically engineered yeast strains are used to make proteins (Hepatitis B vaccine). Taxomyces: Produces anticancer drug taxol. Trichoderma: Produces cellulase. Used to make fruit juice.
Widely distributed. Primarily terrestrial organisms few freshwater or marine. Some pathogenic. Beneficial relationship.
Multicellular, filamentous fungi. Identify by physical appearance, colony characteristics, and reproductive spores. THALLUS: varies in complexity & size ranging from the single cell yeast, multicellular molds to macroscopic puff balls & mushrooms. (rudimentary plant). Pseudomycetes: Schizomycetes, Myxomycetes (Slime molds). Eumycetes: Phycomycetes, Ascomycetes, Basidiomycetes & Fungi imperfecti.
Associated with nutrition and reproduction. Hyphae- has thin rigid cell wall Hyphae are composed of an outercell wall and inner lumen, which contains the cytosol and organells. A plasma membrane surrounds the cytoplasm and lies next to the cell walls. Hyphae (Sing: Hypha): Long filaments of cells joined together by Apical extention. Septate Hyphae: Cells are divided by cross-walls (septa). Coenocytic (Aseptate) hyphae: Long, continuous cells that are not divided by septa. Hyphae grow by elongating at the tips. Apical extention. Each part of a hypha is capable of growth. Vegetative Hypha: Portion that obtains nutrients. Reproductive or Aerial Hypha: Portion connected with reproduction.• Mycelium: Large, visible, filamentous mass made up of many hyphae. Vegetative Mycelium Aerial Mycelium
Unicellular, spherical or ellipsoidal cells, unconnected. Eucaryotic, lack mycelia, Blastospores/blastoconidia Reproduce by mitosis.Reproduce by mitosis: Fission yeasts: Divide evenly to produce two new cells (Schizosaccharomyces). Budding yeasts: Divide unevenly by budding (Saccharomyces). Budding yeasts can form pseudohypha, a short chain of undetached cells. Candida albicans invade tissues through pseudohyphae.Yeasts are facultative anaerobes, which allows them to grow in a variety of environments. When oxygen is available, they carry out aerobic respiration. When oxygen is not available, they ferment carbohydrates to produce ethanol and carbon dioxide.YEAST LIKE FUNGI: Thick walled spore like structure - Chlamydospores/chlamydoconidia.
Can exist as both multicellular fungi (molds) and yeasts. Many pathogenic species. Mold form produces aerial and vegetative hyphae. Yeast form reproduces by budding. Dimorphism in pathogenic fungi typically depends on temperature: At 37oC: Yeast form. At 25oC: Mold form. Histoplasma capsulatum, sportrichum, blastomyces & coccidiodesimnitis. Dimorphism in nonpathogenic fungi may depend on other factors: Carbon dioxide concentration.
NUTRITIONAL ADAPTATIONS OF FUNGIAbsorptive mode.Fungi absorb their food, rather than ingesting it. Fungi grow better at a pH of 5, which is too acidic for most bacteria. Almost all molds are aerobic. Most yeasts are facultative anaerobes. Fungi are more resistant to high osmotic pressure than bacteria. Fungi can grow on substances with very low moisture. Fungi require less nitrogen than bacteria to grow. Fungi can break down complex carbohydrates (wood, paper), that most bacteria cannot. EXTRACELLULAR DIGESTION Primary storage - Glycogen Saprophytes, Parasites & Symbiotic.
ASEXUAL REPRODUCTION BUDDING : Somatic vegetative cell may bud to produce new organisms. SPORES : Asexually or after sexual reproduction, in individual fungus through mitosis & subsequent cell division. Types of spores: Arthroconidia/Arthrospores Chlamydospores: Thick-walled spore formed within a hyphal segment. Sporangiospores: Asexual spore formed within a sac (sporangium). Conidiospores : Unicellular or multicellular spore that is not enclosed in a sac. Blastospores. Sexual spores: Formed by the fusion of nuclei from two opposite mating strains of the same species. New organisms are different from both parents.
Two basic types of reproductive propagules are found in the fungi:(a) Sexual propagules are produced by the fusion of two nuclei that then generally undergo meiosis. Sexual methods of reproduction involve plasmogamy (cytoplasmic fusion of two cells), karyogamy fusion of two nuclei), genetic recombination and meiosis. The resulting haploid spore is said to be asexual spore, e.g. zygospores, ascospores and basidiospores. If a sexual spore is produced only by fusion of a nucleus of one mating type with a nucleus of another mating type (+ and - strains), the fungus is said to be heterothallic. In contrast, homothallic moulds produce sexual spores following the fusion of two nuclei from the same strain.(b) Asexual propagules are termed either spores or conidia depending on their mode of production, and which arise following mitosis of a parent nucleus. Conidia arise either by budding off conidiogenous hyphae or by differentiation of preformed hyphae. Asexual spores are commonly formed by consecutive cleavages of a sporangium. Asexual forms of reproduction represent the major method for the maintenance and dissemination of many fungi.
SEXUAL REPRODUCTION: Union of compatible nuclei Homothallic Heterothallic Gamatangia or hyphae. Dikaryotic stage Eg; zygomycetes the zygote develop into zygospore Ascomycetes - ascospore Basidiomycetes - basidiospore
Zygomycota (Bread Mold) The conjugation fungi Ascomycota - The sac fungi. Basidiomycetes – The club fungi. Deuteromycota
The bread mold/The conjugation fungi/pin moulds. Zygomycetes eg: Rhizopus stolonifier. Aseptate hyphae – haploid and thick walled resting spore.Generally not pathogens. Rhizopus nigricans: Common black bread mold. May cause opportunistic infections in diabetes patients. Rhizopus – produce food – tempeh from soybean Mucor spp – in making cheese – sufu. Anesthetics, birth control agent , etc.
Asexual Reproduction: Used most of the time. Sporangiospore: Asexual spore enclosed within a sporangium or sac at the end on an aerial hypha. - columella, hyphae, stolon, rhizoids. Sexual Reproduction: Occurs through conjugation, the joining of hypha of two different strains (plus and minus). Includes projection Progametangia, multi nucleated gamatangia. Zygospores: Sexual spores which are enclosed in a thick, resistant wall.
Medically important orders and genera include:1. Entomophthorales subcutaneous zygomycosis (Entomophthoromycosis) - Conidiobolus and Basidiobolus.2. Mucorales - subcutaneous and systemic zygomycosis (Mucormycosis) - Rhizopus, Mucor, Rhizomucor, Absidia, Cunninghamella, Mortierella, Saksenaea and Apophysomyces.
Sac fungi., / Common Moulds. Ascomycetes Yeast, blue and green moulds of blue cheese and citrus fruits, cup fungi & edible morels. Saprophytes or parasites. (hypomycetes) Septate, porous, haploid hyphae. Asexual Reproduction: Conidiospores not enclosed in a sac. Become airborne easily. Form chains (broom-like structures). By Conidia. Sexual Reproduction: Ascospores enclosed in a sac-like structure (ascus). Requires Antheridium and Ascogonium – bulbous sexual bodies containing many nuclei (Haploid). Sexual reproduction is by the formation of endogenous ascospores, typically eight, in an ascus. Asci are often housed in a fruiting body or ascocarp e.g. cleistothecia or perithecia. Process include – dikaryogamy , plasmogamy, Synkaryogamy.Include common antibiotic producing fungi and yeasts, and several human pathogens. Penicillium notatum (Produces penicillin) Saccharomyces (Brewer’s yeast) Trychophyton (Athlete’s foot) Aspergillus (Carcinogenic aflatoxin in peanuts), Blastomyces (Respiratory infections) Histoplasma capsulatum (Respiratory and systemic infections) Ergotis – toxic condition in human and animals – accompanied by gangrene, psychotic delusions, nervous spasm, absorption and convulsions.
No classes are now recognized; although in the past they have often beengrouped on how the asci were arranged (Hemiascomycetes, Plectomycetes,Pyrenomycetes, Discomycetes, Laboulbeniomycetes and Loculoascomycetes).
Medically important genera include the teleomorphs of known pathogenic fungi e.g. Arthroderma,Nannizzia, Ajellomyces, Pseudallescheria, Eurotium etc., agents of mycetoma, like Leptosphaeria and Neotestudina, and of black piedra, like Piedraia hortae.Severe nail infection with Trichophyton Disseminated Histoplasmarubrum in a 37-year-old male AIDS patient. capsulatum, skin infection.Source: Intern. J. Dermatol. 31(1992): 453. Source: Microbiology Perspectives, 1999.
YEAST – THE ONE CELLED ASCOMYCETES:Yeast – unicellularForms ascusOval/spherical, cellwall,Vacuole in the cytoplasm & nucleus.Asexually Reproduction: BuddingSexual Reproduction: 2 nuclear division resulting in 4 nuclei. – Ascospores.
The club fungi Have septate hyphae. Include mushrooms, toadstools, rusts, and smuts. Four classes may be distinguished: Hymenomycetes (mushrooms), Gasteromycetes (puff balls), Urediniomycetes (rusts) and Ustilaginomycetes (smuts).Sexual Reproduction: Produce basidiospores: Spores formed externally on a club shaped sexual structure or base called basidium.Asexual Reproduction: Through hyphae.Genera of medical importance include: 1. Teleomorphs of known pathogenic fungi, e.g. Filobasidiella. 2. Coprinus and Schizophyllium agents of basidiomycosis. 3. Mushroom poisoning by Aminita, Lepiota, Coprinus and Psilocybe etc. Cryptococcus: Causes opportunistic respiratory and CNS infections in AIDS patients. Amanita: Mushroom produces lethal toxins to humans. Claviceps purpurea: Produces ergot toxin in wheat and rye.
Deuteromycetes ( secondary fungi) Not known to produce sexual spores. Reproduce asexually. Catch-all category for unclassified fungi: Pneumocystis carinii: Causes pneumonia in AIDS patients. Leading cause of death in AIDS patients. Originally classified as a protozoan. Candida albicans: Causes yeast infections of vagina in women. Opportunistic infections of mucous membranes in AIDS patients.
Source: Atlas of Clinical Oral Pathology, 1999
1 Chytridiomycetes (chytrids) Terrestrial & aquatic fungi. Asexually – motile zoospores with single, posterior, whiplash flagella. Single cell, multinucleate mass/true mycelium. Sexually – zygote formation. Eg: Allomyces.