Kingdom FungiKingdom Fungi

Dr. ROD ALFONSOHead, Development and Quality Assurance Unit

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

MycologyMycology

Mycology is the study of fungi ( yeasts, molds and mushrooms)

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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

Mycelium: Large, Visible Mass of Mycelium: Large, Visible Mass of HyphaeHyphae

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.