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  2. 2. Fungi Chemoheterotrophic Have cell walls typically composed of chitin Do not perform photosynthesis Lack chlorophyll Related to animals
  3. 3. Fungi The Significance of Fungi Decompose dead organisms and recycle their nutrients Help plants absorb water and minerals Used for food and in manufacture of foods and beverages Produce antibiotics 30% cause diseases of plants, animals, and humans Can spoil fruit, pickles, jams, and jellies
  4. 4. I. FUNGI (Mycology)  Diverse group of heterotrophs. Many are ecologically important saprophytes Others are parasites.  Most are multicellular, but yeasts are unicellular.  Most are aerobes or facultative anaerobes.  Cell walls are made up of chitin.  Over 100,000 fungal species identified. Only about 100 are human or animal pathogens. Most human fungal infections are nosocomial and/or occur in immunocompromised individuals.  Fungal diseases in plants cause over 1 billion dollars/year in losses.
  5. 5. CHARACTERISTICS OF FUNGI 1. Yeasts Unicellular fungi, nonfilamentous, typically oval or spherical cells. 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.
  6. 6. CHARACTERISTICS OF FUNGI (Continued) 2. Molds and Fleshy Fungi Multicellular, filamentous fungi. Identified by physical appearance, colony characteristics, and reproductive spores. Thallus: Body of a mold or fleshy fungus. Consists of many hyphae. Hyphae (Sing: Hypha): Long filaments of cells joined together.  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. 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.
  7. 7. Characteristics of Fungal Hyphae: Septate versus Coenocytic 1
  8. 8. Mycelium: Large, Visible Mass of Hyphae 2
  9. 9. CHARACTERISTICS OF FUNGI (Continued) Dimorphic Fungi 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. Dimorphism in nonpathogenic fungi may depend on other factors: Carbon dioxide concentration.
  10. 10. 3
  11. 11. NUTRITIONAL ADAPTATIONS OF FUNGI 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.
  12. 12. FungiNutrition of Fungi Acquire nutrients by absorption Most are saprobes Haustoria allow some to derive nutrients from living plants and animals May use ionizing radiation as energy source
  13. 13. Fungi Reproduction in Fungi All have some means of asexual reproduction involving mitosis and cytokinesis Most also reproduce sexually Budding and asexual spore formation Yeasts bud in manner similar to prokaryotic budding Pseudohypha Series of buds that remain attached to one another and to parent cell Filamentous fungi produce lightweight spores that disperse over large distances
  14. 14. LIFE CYCLE OF FUNGI Filamentous fungi can reproduce asexually by fragmentation of their hyphae. Fungal spores are formed from aerial hyphae and are used for both sexual and asexual reproduction. 1. Asexual spores: Formed by the aerial hyphae of one organism. New organisms are identical to parent.  Conidiospore: Unicellular or multicellular spore that is not enclosed in a sac.  Chlamydospore: Thick-walled spore formed within a hyphal segment.  Sporangiospore: Asexual spore formed within a sac (sporangium). 2. Sexual spores: Formed by the fusion of nuclei from two opposite mating strains of the same species. New organisms are different from both parents.
  15. 15. Tips fuse Dikaryon 2 nuclei per cell Nuclei fuse Meiosis Dikaryotic stage (nn) Diploid stage (2n) Haploid stage (n) 4
  16. 16. Fungi Classification of Fungi Division Zygomycota Division Ascomycota Division Basidiomycota Deuteromycetes
  17. 17. IMPORTANT DIVISIONS OF FUNGI 2. Zygomycota (Conjugation Fungi) Also known as bread molds. Saprophytic molds with coenocytic hyphae Asexual Reproduction: Used most of the time. Sporangiospore: Asexual spore enclosed within a sporangium or sac at the end on an aerial hypha. Sexual Reproduction: Occurs through conjugation, the joining of hypha of two different strains (plus and minus). Zygospores: Sexual spores which are enclosed in a thick, resistant wall.  Generally not pathogens. Rhizopus nigricans: Common black bread mold. May cause opportunistic infections in diabetes patients
  18. 18. Sporangium bursts to release spores. Spore germinates to produce aseptate mycelium (1n). Asexual Reproduction Sexual Reproduction Vegetative mycelium grows. Sporangium (1n) Sporangiospores Aerial hypha produces a sporangium. Sporangio- phore Mating hyphae join and fuse. Dikaryon (nn) Zygosporangium forms. (2n) Zygosporangium matures. Nuclear meioses occurs (not shown). Zygosporangium produces an asexual sporangium (1n). Spores (1n) are released from sporangium. Haploid nuclei (1n) Gamete forms at tip of hypha. Spore germinates. 5
  19. 19. IMPORTANT DIVISIONS OF FUNGI 3. Ascomycota (Sac Fungi) Molds with septate hyphae and some yeasts. Asexual Reproduction: Conidiospores not enclosed in a sac. Become airborne easily. Form chains (broom-like structures).  Sexual Reproduction: Ascospores enclosed in a sac- like structure. 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)
  20. 20. Vegetative mycelium grows. Asexual Reproduction Sexual Reproduction (called Eupenicillium at this stage) Conidiospore germinates to produce mycelium. Conidiospores are released from conidiophore. Ascospores germinate to produce mycelia. Hypha produces conidiophores and conidiospores. Conidiospore Conidiophore Hyphal tip undergoes cytoplasmic fusion with opposite mating type. Dikaryon (nn) forms. Nuclei fuse in terminal cells to form 2n nuclei. Dikaryon Ascus Ascospores Ascus opens to release ascospores. Meiosis produces four haploid (1n) cells. Ascus Ascospore Mitosis produces eight haploid ascospores on each tip. 6
  21. 21. IMPORTANT DIVISIONS OF FUNGI 4. Basidiomycota (Club Fungi) Have septate hyphae. Include mushrooms, toadstools, rusts, and smuts. Sexual Reproduction: Produce basidiospores: Spores formed externally on a club shaped sexual structure or base called basidium.  Asexual Reproduction: Through hyphae.  Examples: 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.
  22. 22. Life Cycle of a Basidiomycete Mushrooms are Produced Sexually 7
  23. 23. IMPORTANT DIVISIONS OF FUNGI 1. Deuteromycota 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.
  24. 24. FUNGAL DISEASES Mycosis: Any fungal disease. Tend to be chronic because fungi grow slowly. Mycoses are classified into the following categories: I. Systemic mycoses: Fungal infections deep within the body. Can affect a number if tissues and organs. Usually caused by fungi that live in the soil and are inhaled. Not contagious. Examples: Histoplasmosis (Histoplasma capsulatum): Initial infection in lungs. Later spreads through blood to most organs. Coccidiomycosis (Coccidioides immites): Resembles tuberculosis.
  25. 25. FUNGAL DISEASES (Continued) III. Subcutaneous mycoses: Fungal infections beneath the skin. Caused by saprophytic fungi that live in soil or on vegetation. Infection occurs by implantation of spores or mycelial fragments into a skin wound. Can spread to lymph vessels. IV. Superficial mycoses: Infections of hair shafts and superficial epidermal cells. Prevalent in tropical climates.
  26. 26. FUNGAL DISEASES (Continued) Opportunistic mycoses: Caused by organisms that are generally harmless unless individual has weakened defenses: AIDS and cancer patients Individuals treated with broad spectrum antibiotics Very old or very young individuals (newborns).  Examples: Aspergillosis: Inhalation of Aspergillus spores. Yeast Infections or Candidiasis: Caused mainly by Candida albicans. Part of normal mouth, esophagus, and vaginal flora.
  27. 27. ECONOMIC IMPORTANCE OF FUNGI 25-50% of harvested fruits and vegetables are damaged by fungi. Fungal infections of plants are commonly called rots, rusts, blights, wilts, and smuts. Phytophthora infestans: Caused great potato famine in mid- 1800s. Over 1 million people died from starvation in Ireland. Many immigrated to the U.S.  Beneficial fungi: 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.
  28. 28. Reference: Images (1 to 7) 1. Microbiology by Gerard J. Tortora, Christine L Case, and Berdell R. Funke Books: 1. Microbiology VI Edition, M.J. Pelczar, E.C.S. Chan and N.R. Kreig, Tata McGraw Hill 2. Brock Biology of Microorganisms (13th Edition) by Michael T. Madigan, John M. Martinko, David Stahl.