Exercise 2_ Morphology and Reproduction of Yeasts

Question 1

are fungi that exist predominantly or solely in a unicellular states.

Answer 1

Yeast

Question 2

Yeats are found on

Answer 2

surfaces of the plant (abundant on the leaves, fruits and nectars of flowers surface (skin), mouth, gastrointestinal tract of animals, and insects

Question 3

Few yeasts are pathogenic to

Answer 3

humans and warm-blooded animals

Question 4

yeast are beneficial in several fermentation processes including

Answer 4

beer, bread and wine

Question 5

Some yeasts are capable of forming

Answer 5

true mycelium and pseudomycelium

Question 6

other terms for pseudomycelium

Answer 6

false mycelium or sprout mycelium

Question 7

a mycelium-like structure consisting of chains of cells formed from sequential budding (sprouting)

Answer 7

pseudomycelium

Question 8

Pseudomycelium can be demonstrated under what environmental condition

Answer 8

reduced oxygen conditions

Question 9

is a vegetative structure that gives rise to arthrospore or blastospore in some species of yeasts

Answer 9

true mycelium

Question 10

in yeast, true mycelium gives rise to

Answer 10

arthrospores and blastospores

Question 11

is an asexual spore (conidium) formed from a pre-existing hypha

Answer 11

arthrospore

Question 12

an asexual spore formed following the marked enlargement of a part of a cell before separation by a septum

Answer 12

blastospore

Question 13

Asexual mode of reproduction in yeast

Answer 13

Budding, fission, as mycelia consisting of septate hyphae

Question 14

an outgrowth develops from the parent cell and eventually separates as a daughter cell

Answer 14

budding

Question 15

the parent cell simply divides and develop into two identical daughter cells

Answer 15

fission

Question 16

sexual reproduction in yeasts

Answer 16

sexual spore formation

Question 17

sexual spores of yeast

Answer 17

ascospore or basidiospore

Question 18

yeast that are imperfect or lacks sexual phase

Answer 18

anamorphic

Question 19

yeast cultures used in the exercise

Answer 19

Candida sp. Saccharomyces sp. Rhodotorula rubra Hansenula sp. Pichia sp.

Question 20

Candida sp.

Answer 20

Budding (pseudomycelia) depending on the species (ascospore or other sexual phase

Question 21

saccharomyces sp.

Answer 21

Budding (pseudomycelia) ascospores

Question 22

Hansenula sp.

Answer 22

Budding Pseudomycelia Ascospores

Question 23

Pichia sp.

Answer 23

Budding Pseudomycelia Ascospores

Question 24

Rhodotorula rubra

Answer 24

Budding Pseudomycelia Basidiospores

Question 25

What is the purpose of the cover slip in Dalmau plate?

Answer 25

It flattens the inoculum for better visualization, it also provides a partial anaerobic condition which encourages yeast to develop hyphae or mycelia or pseudomycelia (for those that cannot develop true mycelia) It also prevent contamination during microscopy

Question 26

How is Schizosaccharomyces morphologically different from Saccharomyces?

Answer 26

Schizosaccharomyces are rod-shaped, divides asexually through fission, develops septa during cell division and develops true mycelia. Whereas, Saccharomyces are oval or round, divides asexually through budding, no septum formation, develops pseudomycelium.

Question 27

Discuss PDA, MA, and AcA in studying yeast cultures.

Answer 27

PDA Potato provides essential nutrients which promotes fungal growth. Dextrose serves as a carbohydrate source for growth stimulants. Slightly acidic pH (~5.6) inhibits bacterial growth and promotes yeasts growth. AcA Sodium acetate as carbon source. Dextrose is the source of carbohydrates/energy. Yeast extract is nutritional resource (essential growth factors, amino acids and minerals) MA Malt extracts provide essential nutrients, amino acids, and vitamins necessary for fungal growth. Limited nitrogen content and carbon availability can induce sporulation in yeasts. Acidic pH inhibits bacterial growth and promote fungal growth.

Question 28

PDA vs. AcA growth

Answer 28

Growth is faster in PDA as it provides more carbon source and other essential nutrients compared to AcA

Question 29

Why is malachite green used in ascospore staining?

Answer 29

It is a small, basic (positively charged) dye It is stable under heat. Heat is required to destabilize proteins in the spore wall and allow entry of malachite green. Once it is trapped inside, it is retained strongly due to the tough and hydrophobic nature of the spore wall.

Question 30

What is the significance of having asexual and sexual modes of reproduction?

Answer 30

Asexual reproduction can be more efficient in terms of energy and time as only one individual is required to produce an offspring, thus, can be used in rapid multiplication in stable environment. Sexual reproduction confers genetic diversity to the next generation necessary for adaptation.

Question 31

What other characteristics should be used to accurately identify yeasts?

Answer 31

pathogenicity (virulence factors), Biochemical and physiological characteristics (enzyme activity, fermentation of sugar, pigment production, Molecular characterization (e.g., DNA sequencing, molecular markers)