AIT101 MICROBIOLOGY Lecture: Yeast Kamonchai Cha-aim, Ph.D.

February 9th, 2015

Outline• History of yeast• Structure and life cycle of yeast • Nature of yeast • Applications of yeast in industries

Objectives• To understand the nature, structures, and life cycles of yeast and mold.

• To explain the applications of yeast for the production of fermented products.

Figure 1. Classification of yeast and mold.

PART I: YEASTSaccharomyces cerevisiae

General Characteristics of Yeast• Eukaryotic microorganism• Unicellular or multicellular• About 1,500 species

• Are all yeast useful?• Cell size 3-6 μm or up to >40 μm• Shape: oval, sphere, cylindrical, elongate form • Sexual or asexual reproduction (budding mitosis)• Symmetric or asymmetric division• Fermentation (not all yeast)• Pathogens causing infection in human

History of Yeast• Egyptian (4000 B.C.) made bread and wine.• However, nobody know what was the microbe play an important role for the biochemical process of fermentation……

….Until 1857…

Louis Pasteur discovered yeast

History of Yeast

History of Yeast• Yeast has been used for proteins production since 1980. For example; Insulin, enzymes such as amylase, lipase, phosphatase• In 1996, DNA sequencing of Saccharomyces cerevisiae

was completed. • www.yeastgenome.org• 5,800 genes were identified

• Essential gene • Nonessential gene

Figure 2. Homepage of SGD.

Structure and life cycle of Yeast• Cell Structure

Figure 3. Drawing diagram of yeast cell.

Structure and life cycle of Yeast• Yeast Cell Wall

Figure 4. Component of yeast cell wall.Periplasmic space

Structure and life cycle of Yeast• Yeast Cell Wall

Mannoprotein; Yeast wall mannoproteins are highly glycosylated polypeptides, often 50 to 95% carbohydrate by weight.

Sugar can add 50,000 to 100,000 Da to the size of the mannoproteins.

Structure and life cycle of Yeast• Yeast Cell Wall

Glucan; The major component (about 85%) is a branched β-(1→3)-glucan of high molecular weight (about 240000) containing 3% of β-(1→6)-glucosidic interchain linkages.

The minor component is a branched β-(1→6)-glucan.

Structure and life cycle of Yeast• Yeast Cell Wall

Glucan structure

Figure 5. β-(1→3)-glucan linked β-(1→6)-glucosidic interchain glucan polymer

Structure and life cycle of Yeast• Yeast Cell Wall

Chitin; is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose.

Figure 6. Units of N-acetylglucosamine; a polymer of chitin

Structure and life cycle of Yeast• Yeast Cell Wall

Membrane; selective permeable, protect cell, phospholipid bilayer and proteins

Structure and life cycle of Yeast• Nucleus; The main function of the cell nucleus is to control

gene expression and mediate the replication of DNA during the cell cycle.

Structure and life cycle of Yeast• Nucleus; Yeast Chromosome

Structure and life cycle of Yeast• Nucleus; DAPI staining yeast nucleus(4',6-diamidino-2-phenylindole)Hoechst33342 (Bisbenzimid)

Structure and life cycle of Yeast• Vacuole; is essentially enclosed compartments which are

filled with water containing inorganic and organic molecules including enzymes in solution.

Structure and life cycle of Yeast Vacuole; In general, the functions of the vacuole include:• Isolating materials that might be harmful or a threat to the

cell• Containing waste products• Containing water in plant cells• Maintaining internal hydrostatic pressure within the cell• Maintaining an acidic internal pH• Containing small molecules• Exporting unwanted substances from the cell

Structure and life cycle of Yeast• Life cycle

Structure and life cycle of Yeast• Budding Yeast Life cycle

Two types of pheromoneMAT a MAT α

Receptor binding protein

Shmoo structure

Binding Yeast Cell

http://www.jove.com/science-education/5097/yeast-reproduction

Structure and life cycle of Yeast• Budding Yeast (G1 S G2 and M Phase)

Structure and life cycle of Yeast• Nitrogen starvation in budding Yeast (Sporulation)

Sporulation Medium:10 g/l Potassium acetate1 g/l Yeast extract0.5 g/l Dextrose

YPD Medium:20 g/l Peptone10 g/l Yeast extract20 g/l Dextrose

1 µM

Structure and life cycle of Yeast• Fission Yeast Life cycle

Structure and life cycle of Yeast• Fission Yeast Life cycle

Figure 7. A generation time of S. pombe between 2 and 4 hours

Nature of Yeast and Mold Where is yeast found in nature?• On the skins of fruits and berries ( such as grapes,

apples, or peaches)• In exudates from plants (such as plant saps or cacti)• Some yeasts are found in association with soil and

insects.

Nature of Yeast and MoldYeast and Temperature• Cool temperature (below 15oC) Stress Condition Dormancy cells

• Warm temperature (15 – 30oC)

Optimal temperature for rapid growth yeast (25-35oC)

• High temperature (40oC)Stress Condition Arrest growth

Application of Yeast• Bioethanol • Beer-wine industry• Bread• Source of protein/vitamin• Make vaccine of Hepatitis B (recombinant DNA)• Making Interferon• b-glucan• Mannoprotein: wine clarification

Applications of yeast and mold in industries

Yeast• Saccharomyces cerevisiae• S. carlbergensis• Kluyveromyces marxianus• Saccharomycopsis fibuligera

How to utilize them?• Alcoholic beverage by sugar fermentation• Baking bread• Nutritional supplements• Yeast extract• Enzymes production

Applications of yeast and mold in industries• Alcoholic beverage by sugar fermentation

Figure 11. Scheme of glucose metabolic pathway to produce ethanol

Applications of yeast and mold in industries• Baking bread

Anaerobic respiration in yeast:  Glucose   Pyruvate   Ethanol + CO2

ALKOSEL® R397• ALKOSEL® R397 is a specific inactivated whole cell yeast

(Saccharomyces cerevisiae) product containing the essential trace element selenium in its natural food form, L(+) selenomethionine.

• It is produced by growing yeast in the presence of measured amounts of selenium. This specific yeast strain absorbs selenium and biochemically transforms it into the highly bioavailable L(+) selenomethionine and other seleno-proteins.

• Selenomethionine is naturally found in edible plant protein but only at very low concentration. It is the most suitable form of selenium for animal nutrition.

Applications of yeast and mold in industries

Applications of yeast and mold in industries

• Nutritional supplements Yeast Dietary Supplement

Applications of yeast and mold in industries

• Yeast extract

Applications of yeast and mold in industries

• Saccharomycopsis fibuligera

Mycelial mat hypha Starch degradation (showed clear zone)