Week 1: Fungal growth and morphogenesis 3

Question 1

What can gorwth be defined as?

Answer 1

orderly increase in cell components leading to an increase in biomass

Question 2

What do many concepts in growth microbiology derive from?

Answer 2

unicellular organisms – bacteria – concentrate on population growth rather than individuals

Question 3

What are the more complex concept in filamentous growth of fungi?

Answer 3

Extension is localized at the hyphal tip
Biomass synthesis may occur throughout the mycelium
Pellet formation in liquid media
Colony heterogeneity on solid media

Question 4

How does the individual hyphae grow?

Answer 4

Hyphae extend by incorporation of new wall material and membrane at the apical tip

Question 5

What are the stages in hyphae growth?

Answer 5

spore germination - utilisation of storage compounds

germ tube growth - nutrient uptake and biosynthesis

hyphae - extension rate accelerates - growth becomes autocatalytic

Question 6

What is it called when extension rate accelerates?

Answer 6

hypha growth becomes autocatalytic

Question 7

How would you describe the early growth of an individual hypha?

Answer 7

exponential, through autocatalysis
Longer hyphae make more secretory vesicles, which are delivered to the growing apex – more vesicles – faster growth

Question 8

Can exponentail growth procees indefonetly?

Answer 8

NO

Question 9

Can exponentail growth procees indefonetly?

Answer 9

NO

Question 10

What happens to hyphae growth after exponential growth?

Answer 10

linear growth

Question 11

When does linear growth occur?

Answer 11

can happen after a short amount of time growing

Question 12

What happens during linear growth?

Answer 12

May result from septa formation that limit transport to the hyphal tip

Question 13

Do branches promote exponential?

Answer 13

YES, Though individual hyphae may extend linearly at a constant rate, exponential growth is possible through branch formation

Branch formation ≡ Cell division in unicellular organisms

Exponential growth therefore occurs through an exponential increase in the number of branches, each extending at a constant rate

Question 14

How do you calculate the hyphal growth unit?

Answer 14

G= total mycelial length / total number of branches

Question 15

What letter defibes the hyphal growth unit?

Answer 15

G

Question 16

How does the hyphal growth unit value increase?

Answer 16

G increase through growth then oscillates until branches are formed continuously and G remains constant

Question 17

What letter defines the mean hyphal extension rate?

Answer 17

E

Question 18

How do you calculate E (mean hyphal extension rate)?

Answer 18

E = μG
μ = specific growth rate

Question 19

How does the length of the mycelial exponentially grow?

Answer 19

The length of the hyphae increases but eventually turns to linear growth, as this occurs the number of hyphae tips increases and continues the cycle of exponential growth in the mycelial

Question 20

How is growth maintained exponentially?

Answer 20

when measured in terms of total mycelial length, is exponential as a result of exponential branch formation

Question 21

How can the growth model be redefined?

Answer 21

• During extension of a hypha, a new branch is initiated when the mean volume of cytoplasm per hyphal tip (the hyphal growth unit) exceeds a particular critical value.
• If the hyphal growth unit is ‘the mean volume of cytoplasm per hyphal tip’ it can be calculated as the ratio of total mycelial length to total number of hyphal tips.

Question 22

How can the hyphal growth unit be defined?

Answer 22

the hyphal growth unit can be interpreted as the average volume of cytoplasm (equivalent to average length of hypha of uniform diameter) necessary to support the extension growth of a single average hyphal apex.

Question 23

Does hyphal extension still occur when nutrients are limited?

Answer 23

YES, It is important that hyphal extension is maintained to explore new regions and find nutrients despite nutrient limitation

Question 24

Does branching occur when nutrients are sparse?

Answer 24

Under nutrient-poor conditions – branching is sparse

Under nutrient-rich regions – branching is extensive

Question 25

Are the kinetics of colony growth the same as individual hyphae?

Answer 25

YES
Kinetics of colony growth the same as for individual hyphae, i.e. radius increases exponentially but becomes linear when the hyphae extend at a constant rate

Question 26

How do colonies grow exponentially?

Answer 26

colony exponential growth results from growth and branching of a ring of hyphae at the margin of the colony – the peripheral growth zone

Here, the mycelium grows exponentially (≡ same rate in liquid medium)

Question 27

What is the growth called at the end of a colony?

Answer 27

peripheral growth zone

Question 28

Where is the most differentiated (mature) mycelia in a colony?

Answer 28

centre

Question 29

What are the zones from the centre to edges of a colony?

Answer 29

aging zone
fruiting zone
productive zone
peripheral zone

Question 30

What can happen at the centre of a colony?

Answer 30

Autolysis in older (central) region of the colony

Question 31

Why can autolysis occur at the centre of a colony?

Answer 31

Autolysis = “self-lysis” - nutrient exhaustion under centre of colony
Breakdown products reabsorbed by adjacent hyphae

Question 32

What is similar about fungi and bacterial growth kinetics?

Answer 32

lag, log, linear, slowing, stationary, autolytic

Question 33

How do funci ( a part from yeast) grow in liquid cultiure?

Answer 33

In liquid culture, there may be dispersed growth or pellets - spherical or ellipsoidal, variable internal structure

result from aggregation of spores, germ tubes or mycelia

Question 34

Are there differences in the aerobic environment in fungi growing in liquid culture?

Answer 34

proportion of the biomass inactive, the centre as it is in anaerobic conditions

Question 35

What is a hyphal tropism?

Answer 35

A tropism is an orientation response of a hypha to an external stimulus

good chemical - glucose/hormone - grow towards e.g. wood block
bad chemical - toxic - grow away

Question 36

What is a hyphal anastomosis?

Answer 36

hyphae connecting tip to tip or branch to branch
network of hyphae, joining up of individual colonies to one large colony which is more efficient at exploring and exploiting the substrate