Saccharomyces cerevisiae (yeast and mold)

Question 1

what is a fungus?

Answer 1

any of a group of spore-producing organisms feeding on organic matter, including molds, yeast, mushrooms, and toadstools.

Question 2

what is mold?

Answer 2

is afungusthat grows in the form ofmulticellular filaments calledhyphae

Question 3

what is yeast?

Answer 3

a microscopic fungus consisting of single oval cells that reproduce by budding, and are capable of converting sugar into alcohol and carbon dioxide.

Question 4

what is Saccharomyces cerevisiae?

Answer 4

• a species of budding yeast
• eukaryotic organism
• “sugar-mold”: good at metabolizing sugar
• It is instrumental to winemaking, baking, and brewing
• it is not airborne, needs a vector to move (humans, bumblebees)

Question 5

what is Saccharomyces cerevisiae known for?

Answer 5

its ability to utilize carbohydrates in the formation of ethanol and other by-products

Question 6

Gay-Lussac Equation:

Answer 6

180g sugar is converted to 92g Ethanol and 88g CO2

Question 7

cell cycle of Saccharomyces cerevisiae

Answer 7

• S. cerevisiae is a budding yeast
• Sc can exist as both a haploid or a diploid
• If adequate nutrients are present both haploids and diploids can undergo repeated rounds of vegetative growth and mitosis
• When nutrients become depleted, both haploids and diploids arrest as stationary phase cells
• > Stationary phase cells are morphologically and biochemically distinct from proliferating yeast cells. They are round, and bright and contain much higher levels of storage carbohydrates (trehalose and glycogen) than proliferating cells. Stationary phase cells also have an increased resistance to a number of stresses and environmental conditions when compared to growing cells

Question 8

haploid cells of Saccharomyces cerevisiae

Answer 8

cells can exist in one of two mating types a or 𝝰:
- Mating type a produce a pheromone ‘a factor’
- Mating type 𝝰 produce a pheromone ‘𝝰 factor’
Each cell type has the surface receptor for the opposite mating type. If the surface receptor is stimulated the cells arrest in the G1 phase of their cell cycle. These cells no longer proliferate, but start growing toward each other => The resultant shape is called a ‘shmoo’. Eventually there is cell contact, fusion, and a diploid is formed

Question 9

Four haploid spores of Saccharomyces cerevisiae are formed and contained in an …

Answer 9

ascus (even greater resistance to environmental factors than stationary phase cells)

Question 10

Saccharomyces cerevisiae vegetative proliferation occurs via ….

Answer 10

budding

Question 11

What are some morphogenic aspects of the yeast cell cycle?

Answer 11

• Bud site selection: in rich media haploids bud in an axial pattern where diploids show polar budding
• Polarity
• Pattern
• Rate of growth

Question 12

2 examples of checkpoint controls where the progression of the cell cycle is prevented if certain necessary processes have not taken place

Answer 12

• Mitosis will not happen if DNA replication has not been completed
• Since yeast has a cell wall, growth can only occur where new cell wall material and cell wall remodeling enzymes are delivered.

Question 13

when nutrients are depletes, cell cycling stops and the cells are arrested in a ….

Answer 13

stationary phase

Question 14

Growing Sc cells ferment … via … to form …

Answer 14

glucose
glycolysis
ethanol

Question 15

when does “over-fermentation” occur with Saccharomyces cerevisiae?

Answer 15

In Stationary phase cells use the ethanol formed in earlier stages via the TCA and glyoxylate cycles. This does not occur if you produce a ferment with high enough ethanol [can’t use thanol]

Question 16

Most compounds required for Sc metabolism are not able to pass through the phospholipid membrane, and therefore must be transported via specific transport proteins
… and … are exceptions to this rule and can diffuse easily across the cell membrane

Answer 16

Ethanol and Glycerol

Question 17

what happens to carbohydrates required for Saccharomyces cerevisiae metabolism?

Answer 17

Some carbohydrates, specifically disaccharides, undergo extracellular hydrolysis by secreted invertase or galactosidase, and the resultant hexoses are taken up by the cell
+ active transport (38 identified carbohydrate transport systems, that transport things like: glycerol, inositol, hexoses, maltose, sucrose, trehalose, lactate, and pyruvate (0.6% of its genome))

Question 18

… is an important carbon source for yeast during brewing and bread-making. Describe its transport/metabolism

Answer 18

Maltose
actively transported across the cellular membrane, and then hydrolyzed via 𝝰-glucosidase (AKA maltase) into two glucose molecules
The glucose is then catabolized via the glycolytic pathway

Question 19

… can be hydrolyzed into fructose and glucose by Sc by an enzyme called invertase.
Describe its transport system.

Answer 19

Sucrose
Sc has a cytoplasmic invertase that requires uptake of the sucrose before catabolism, and an invertase in the periplasmic space
If sucrose is catabolized in the periplasmic space the resultant hexoses can easily be taken up by hexose transporters

Question 20

Glucose and hexoses are further catabolized to … via glycolysis. No net … occurs in the process

Answer 20

pyruvate

oxidation

Question 21

cell wall of Saccaromyces cerevisiae

Answer 21

• offers mechanical strength against physical damage and plays a major role in morphogenesis
• consists of a homogenous inner layer (plasma membrane) and a fibrillar outer layer implanted in the inner layer and emanating from the cell surface
• Glucans compose approximately 50% of the cell wall, while mannoproteins make up 40% and Chitin accounts for the remaining 10% but gives it the strength

Question 22

… is largely responsible for the mechanical strength of the cell wall

Answer 22

chitin

Question 23

Aspergillus oryzae is a …/….

it secretes a selection of …. that extracellularly degrade …. into ….

Answer 23

mold/filamentous fungi
amylases
starch into glucose

Question 24

what are the 3 main species of amylases + mode of action

Answer 24

• endoamylases (cleave bond in the middle of chain)
• exoamylases (cleave bond at the end of chain)
• debranchign enzyme (cleave bond at branch section)

Question 25

what is a conidium?

If the conditions are right the conidium will swell and eventually grow into a … that will eventually form the …

Answer 25

a spore that is produced asexually by A. oryzae fungi at the tip of a specialized hypha that is capable of growing into a new multicellular organism

• germ tube
• hyphae

Question 26

what are hyphae?

Answer 26

the individual sections that are partitioned by septa and constitute multicellular filamentous fungi

Question 27

what is the function of the pore located in the middle of each septum? what structure intervenes if cell damage is detected?

Answer 27

it allows for communication between cells. If one cell is killed or damaged it presents a danger to the entire organism, Woronin bodies are grouped near the septum and will plug the pore if it detects cell damage

Question 28

A. oryzae contain a specific organelle called a Spitzenkorper. Where is it located and what is its function?

Answer 28

present in the hyphal tip region and is involved in the accumulation and secretion of vesicles that contain secretory enzymes

Question 29

how does secretion of vesicles containing secretory enzymes work?

Answer 29

• Spitzenkorper secrete vesicles containing secretory enzymes
• Secretion of enzymes happens very quickly
• The secretion vesical is then endocytosed immediately after fusion with the cell membrane, and is then immediately recycled for incorporation into new secretion vesicles
  => This recycling is critical for sustaining high levels of amylases by A. oryzae

Question 30

what is the role of conidiophore cell?

Answer 30

designed to produce conidium to spread the mold

Question 31

what is the mechanism to A. oryzae spreading?

Answer 31

• Nutrients are passed from the hyphae and up into the budding conidia
• When conditions are right the conidium prepares to germinate. The first step is to swell
• Vacuoles involved in autophagy begin to appear and grow, and aid in the physical extrusion of the cytoplasm at the tips of the germ tubes

Question 32

what is Geotrichum candidum

Answer 32

A rapid growing mold that prevents unwanted mold growth in moist cheeses. Several varieties are available including Geo13 which produces intermediate flavor, Geo15 is mild, and Geo17 is very mild (cheese making)

Question 33

what is Penicillium candidum

Answer 33

Produces the fuzzy white mold on the surface of bloomy rind cheeses including Brie, Camembert, Coulommiers, and French goat cheeses. Various strains can be used to produce a range in flavours

Question 34

what is Penicillium roqueforti

Answer 34

Creates the colored veins and surfaces and is a major contributor to the flavor in blue cheeses including Gorgonzola, Roquefort, and Stilton. Various strains are used to get a range in colours including grey, green, and blue.

Question 35

How does microbial co-existence in traditional fermentations work?

Answer 35

symbiotic mix of yeast, mold, LAB, and AAB

• LAB usually require various nutrients, such as amino acids and vitamins
• Yeast and mold provide nutrients to LAB

Question 36

in traditional fermentations … and … are usually on the surface, while … and … are internal. Why?

Answer 36

mold and AAB

because LAB and yeasts are anaerobic, Mold and AAB are aerobic

Question 37

what is sake?

Answer 37

traditional Japanese alcoholic drink
uses mold, yeast, LAB BUT NO AAB
ferments rice

Question 38

how Is sake made?

Answer 38

• koji is used to convert the starches in rice into sugars
• In certain varieties of Sake (Kimoto-type) LAB can colonize the sugar and grow for a second stage of the fermentation
• This kills wild yeast which prepares the solution for the fermentation by the brewing yeast

Question 39

how does Fukuyama pot vinegar differ from sake?

Answer 39

Rice and koji are added without additional microorganisms to a loosely capped large pot and laid in an open-air field

Question 40

what are the 3 reaction steps involved in Fukuyama pot vinegar?

Answer 40

Saccharification
Alcohol fermentation
Acetic acid fermentation
Lactic acid fermentation

Question 41

how is milk kefir made?

Answer 41

• milk is inoculated with kefir grains that harbor LAB, AAB, and yeast (and sometimes molds)
• Kefir grains consist of water and water-insoluble kefiran that is an extracellular polysaccharide that is produced by the LAB

Question 42

Milk kefir grains are generally used to start a culture via … , since they increase after each fermentation batch

Answer 42

back slopping

Question 43

In kefir grains the main Extracellular polysaccharide substance produced is called …

Answer 43

kefiran

Question 44

what is kefiran?

Answer 44

a heteropolysaccharide composed by equal proportions of glucose and galactose and is mainly produced byLactobacillus kefiranofaciens

Question 45

how can we observe the importance of the symbiosis between bacteria and yeast present in kefir?

Answer 45

Despite good kefiran production byL. kefiranofaciensalone, it has been observed that the addition ofSaccharomycessp. to the culture improves the net quantity of kefiran

Question 46

which LAB in kefir? what are their role?

Answer 46

Lactobacillus, Lactococcus, Streptococcus, and Leuconostoc

-> responsible for the acidification of the kefir – shelf-stable

Question 47

which yeast in kefir?

Answer 47

Saccharomyces, Kazachstania, Kluyveromyces, Torulaspora, Pichia, Lachancea, and Yarrowia