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.

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 Spores Budding Saccharomyces cerevisiae Schizosaccharomyces octosporus

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.

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