Introduction to Lab 5: Ex. Fungi – Yeasts
The objectives of this lab is are:
1. To characterize the Yeast fungus.
2. To distinguish various types of Yeasts.
3. To be able to identify those various types of yeasts with the
microscope.
4. To be able to prepare wet mounts of Yeast and visualize them
under 100x oil immersion.
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
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
Budding
Saccharomyces cerevisiae
Spores
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.
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)
– The three Deuteromycotina
•Examples: Trigonopsis, Rhodotorula, and Candida.
Trigonopsis (Demo Slide):
 Triangular cell morphology.
 Budding yeast with buds arising at the apices.
Rhodotorula (Demo Slide):
 Orange/red pigmented colony morphology.
 Budding yeast.
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.
Exercises:
1. Prepare and observe (under 100X magnification) wet mounts of:
• Saccharomyces serevisiae
• Schizosaccharomyces octosporus
2.
Observe stained demo slides of:
• Trigonopsis sp.
• Rhodotorula sp.
• Candida sp.