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Requirements to get Good Requirements to get Good GradeGrade
1. Perfect Attendance
2. Participate actively in classroom activities
3. Pass assignment on time
4. Pass all quizzes and major exams
5. Good attitude
Learning ObjectivesLearning ObjectivesAt the end of the lesson, students will be able to:
1.Define mycology; Define a fungus
2.Describe the characteristics of fungi
3.Describe the distribution of fungi in nature
4.Explain why there are few invasive fungal infection.5.Describe the characteristics of yeasts and how they reproduce
6.Discuss the significance of yeast in food industry, in medicine and biofuel industry.
7.Describe molds
8.Differentiate hypha, thallus and mycelium
9.Differentiate between septate and coenocytic hyphae
10.Explain dimorphic fungi
11.Discuss the beneficial and harmful effects of fungi
What is a fungus? What is a fungus?
• A eukaryotic, heterotrophic organism devoid of chlorophyll that obtains its nutrients by absorption, and reproduces by spores.
• The primary carbohydrate storage product of fungi is glycogen.
• Most fungi have a thallus composed of hyphae (sing. hypha) that elongate by tip growth
The Characteristics of FungiThe Characteristics of Fungi* Eukaryotic(true
nucleus)* Larger, more complex
than bacteria* Lack chlorophyll* Chitin, glucan &
mannan are the complex carbohydrates found in their cell wall
* Reproduce sexually and asexually
* Cell wall contains ergosterol
* Heterotrophic (require organic carbon)
Fungal Fast FactsFungal Fast Facts• Fungi are all
around us
• We touch them, we swallow them, we breathe them
• There are more than 1.5 million fungal species in nature
• Yet only about 100 cause human disease
• Most cause superficial infections, some cause allergic reactions
• Few cause invasive infections
Host/Pathogen Balance:Normal Circumstances
Host Factors
Anatomical barriers
Adaptive immunity
Innate defenses
Virulence
Fungal Burden
Fungal Factors
Protection Infection
Why so few Invasive Infections?
Yeast - Major Yeast - Major CharacteristicsCharacteristics
• Unicellular Fungi, nonfilamentous, oval or spherical cells
• Eukaryotic• Facultative anaerobes
* When oxygen is available, they
carry out aerobic respiration.
* When oxygen is not available, they
ferment carbohydrates to produce
ethanol and carbon dioxide.
• Capable of forming colonies on solid culture media (see pictures on
the right).
They reproduce either asexually (most common) or sexually.•Asexual reproduction is through budding or binary fission. •Sexual reproduction (if any) results in the formation of the appropriate spore structure.
Budding
Yeast - Reproduction
Fission
SporesSaccharomyces cerevisiae
Schizosaccharomyces octosporus
Yeast Significance
Food Industry• Fermentation of bread, beer, and wine. E.g. Saccharomyces cerevisiae (also called baker’s yeast or sugar yeast) used in baking and fermenting of alcoholic beverages.
Medical • E.g. Candida albicans - common in the human mouth, but can become pathogenic and cause Candidiasis (oral and/or genital infection).
Biofuel Industry•Production of ethanol for car fuel.
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.
Characteristics of Fungal Hyphae:Characteristics of Fungal Hyphae:Septate versus CoenocyticSeptate versus Coenocytic
HyphaeHyphae
• Tubular
• Hard wall of chitin
• Crosswalls may form compartments (± cells)
• Multinucleate
• Grow at tips
Hyphal growthHyphal growth• Hyphae grow from their tips
• Mycelium = extensive, feeding web of hyphae
• Mycelia are the ecologically active bodies of fungi
This wall is rigid Only the tip wall is plastic and stretches
Dimorphic FungiDimorphic Fungi Can exist as both multicellular fungi (molds) and yeasts.Can exist as both multicellular fungi (molds) and yeasts.
Many pathogenic species.Many pathogenic species. Mold form produces aerial and vegetative hyphae.Mold form produces aerial and vegetative hyphae.
Yeast form reproduces by budding.Yeast form reproduces by budding.
Dimorphism in pathogenic fungi typically depends on Dimorphism in pathogenic fungi typically depends on
temperature:temperature: At 37At 37ooC: Yeast form.C: Yeast form.
At 25At 25ooC: Mold form.C: Mold form.
Dimorphism in nonpathogenic fungi may depend on other Dimorphism in nonpathogenic fungi may depend on other
factors: Carbon dioxide concentration.factors: Carbon dioxide concentration.
Yeast at 370C Mold at 250C
HUMAN-FUNGUS INTERACTIONSHUMAN-FUNGUS INTERACTIONS
• Beneficial Effects of Fungi * Decomposition - nutrient and carbon recycling. * Biosynthetic factories. Can be used to produce drugs, antibiotics,
alcohol, acids, food (e.g., fermented products, mushrooms). * Model organisms for biochemical and genetic studies.
• Harmful Effects of Fungi * Destruction of food, lumber, paper, and cloth. * Animal and human diseases, including allergies. * Toxins produced by poisonous mushrooms and within food (e.g.,
grain, cheese, etc.). * Plant diseases.