1. Introduction to Lab 5: Ex. Fungi – Yeasts
The objectives of this lab is are:
To characterize the Yeast fungus.
To distinguish various types of Yeasts.
To be able to identify those various types of yeasts with the microscope.
To be able to prepare wet mounts of Yeast and visualize them under 100x oil immersion.

2. Yeast - Major Characteristics
Unicellular Fungi
Eukaryotic
Facultative anaerobes
Capable of forming colonies on solid culture media (see pictures on the right).
Occur worldwide
Over 1,500 species described

3. Yeast - Reproduction
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.
Fission
Spores
Budding
Saccharomyces cerevisiae
Schizosaccharomyces octosporus

4. Yeast Significance Medical Biofuel Industry 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.

5. Yeast - Taxonomy
Yeasts are identified primarily by their biochemical properties.
They are found only in 3 groups of fungi:
Ascomycotina
Examples: Saccharomyces cerevisiae and Schizosaccharomyces octosporus
Deuteromycotina
Examples: Trigonopsis, Rhodotorula, and Candida.
Basidiomycotina (no examples available in lab)

6. The three Deuteromycotina
Examples: Trigonopsis, Rhodotorula, and Candida.
Trigonopsis (Demo Slide):
Triangular cell morphology.
Budding yeast with buds arising at the apices.

7. Rhodotorula (Demo Slide):
Orange/red pigmented colony morphology.
Budding yeast.

8. Candida (Demo Slide):
Pseudohyphae formation – this is formed by repeated budding process where the buds do not separate from the parent cell.
This genus is an opportunistic pathogen and can cause a variety of human infections.

9. Exercises:
Prepare and observe (under 100X magnification) wet mounts of:
Saccharomyces serevisiae
Schizosaccharomyces octosporus
Observe stained demo slides of:
Trigonopsis sp.
Rhodotorula sp.
Candida sp.