BIOS-110 Fungal Biology

Lecture 3 - Fungal nutrition, growth and

reproduction

• Describe the features of a typical mycelial colony and how this relates to what we know about how fungi grow

• Outline the two ways in which yeast cells divide

• Define heterotrophic nutrition and describe how fungi obtain their nutrition

• Describe how a fairy ring is formed (structure and nutrition of the fairy ring fungus).

• Outline the different functions of spores.

• Outline the different spore dispersal mechanisms.

Tip initiation and branching

• Apical dominance occurs in hyphae

• Several factors influence branching

• Higher nutrient quality of growth medium →

more branches → dense mycelium

• Mycelial regulation – some evidence

• Branch position, often behind septum – vesicle

trapping?

Fungionline.org.uk/images/1intro/hyphae1.JPG

Powdery mildew on pea

Mycelium and sporesMycelium of Sclerotinia

infecting beans

Hyphae of Athlete foot fungus

http://www.gettyimages.co.nz/detail/illustration/athletes-foot-fungus-

stock-graphic/125744200

Image from MAF slides

http://msue.anr.msu.edu/news/managemen

t_of_soybean_white_mold

Image from MAF slides

Powdery mildew (Erysiphe pisi)

Germinating spore

Hyphae – branching

and growing

Colony forming

Upright branches in older part of colonySporulation, chains of spores

Falloon et al. 1989. Can. J Bot 67: 3410-3416. Image: RE Falloon, PW Sutherland & IC Hallett

Image: RE Falloon, PW Sutherland & IC Hallett

Image: RE Falloon, PW Sutherland & IC Hallett

Colony profile

1. Apical growth means that

• Mycelium expands in

diameter

• Often circular or spherical shape

• Limited only by nutrients

• Outer edges of mycelium youngest and inner regions oldest

• The largest organism (by area) is a fungus –Armillaria spp. (honey fungus) colony in a forest in Oregon

• Diameter 8.9 km (890 hectares/2200 acres)

• Total colony mass 605 tons

• Estimated to be 2400 years old

From: Young persons guide to the Fungi

Kendrick A

2. Outer hyphae grow towards fresh food substrates

– drives growth

3. Hyphal branches may fuse where they touch

(anastomose)

Rhizoctonia solani hyphal anastomosis

From Modern Mycology, Deacon

4. In older regions of the

mycelium, substrate nutrients

exhausted, so growth

ceases;

→ Existing components used

to produce spores

→ Hyphae die (autolysis)

Image E. Bourguignon LU

Ring worm on scalp

Botrytis cinerea rot of grape berriesBotrytis cinerea lesion on

grape leaf

Basket fungus (Ileodictyon cibarium)

https://www.flickr.com/photos/essjay/164675851

http://www.mattersingray.com.au/h73rdr53s/staff_room/magazines/images/ringworm.jpg

http://djsgrowers.blogspot.co.nz/2013/01/what-is-difference-between-noble-rot.html

Unicellular fungi• Yeasts most common types

• Cell structure similar to hyphal compartment

Sacchromyces internal structure

(from Microbiology, Prescott )

http://www.rpi.edu/dept/chem-eng/Biotech-Environ/beer/yeast/yeast2.htm

Growth by increase in number of individuals. Two ways:-

• Fission

Each cell grows to maximum size, doubles all components, new wall divides cell through centre

• Budding

Parent cell produces a small ‘knob’ on outside which grows until large enough to be independent – is ‘walled’ off.

N.B. High rate of

multiplication1 cell → 1 billion in 10 h

Dimorphic fungi

• These convert between mycelial and unicellular forms.

Environment changes trigger it

https://www.broadinstitute.org/files/news/images/2011/schizo-fissionyeast-v2.jpg

ppdictionary.com/fungi

From: Fungi, man and his environment, Cook RC

Nutrition

Heterotrophic – preformed organic material

1. External digestion

• fungi grow into/next to food sources

• hyphal tip secrete enzymes to OUTSIDE

• degrade food into small soluble

molecules

2. Adsorptive nutrition

Breakdown product absorbed, often by cells

in position 3-10 behind tip

E

E E

EE

EE

E

EE

E E

Enzymes

E

polysaccharide

E

E

E

E

TIME 0

TIME 12h

TIME 24h

TIME 36h

Image Eirian Jones

Nutrition

3. Complex enzyme systems

Enzymes ‘turned’ on & off in response to

nutrient types

4. Excretion of wastes, antibiotics etc.

Causes ‘staling’ of medium

Commonly seen fungal growths

1. Foliar diseases

e.g. Botrytis rot in grapes

Botrytis cinerea rot of grape berries

http://djsgrowers.blogspot.co.nz/2013/01/what-is-difference-between-noble-rot.html

2. Ringworm in humans and animals

• Symptoms – expanding, itchy, pink rings on

skin

• Centre of lesions are dry and scaly

• Transmission - usually by dead skin cells

on furniture etc.

- rarely from animals

https://i.ytimg.com/vi/G2U1CbMazQg/hqdefault.jpg

http://www.mattersingray.com.au/h73rdr53s/staff_room/magazines/images/ringworm.jpg

3. Fairy rings

• Expanding rings of lush grass

growth in pasture and lawns

• Fungus grows in soil

• At advancing front, it produces enzymes which

degrade soil organic matter

→ nutrients products into soil

→ Absorbed by fungus & adjoining grass roots

→ Lush grass growth

• Fungal front grows on

• Behind, a starvation zone (water, nutrients efficient

fungus) → grass dies

also produces Hydrocyanic acid – toxic to grass roots

• As old fungal hyphae break down, they release their

components into the soil → grass recovers

http://www.interhort.com/_images/_cms/Image

/Fairy_Ring_400.jpg

Fungus grows 10-15 cm /year

Fungal colony

Advancing edge of

fungal colony

http://www.cpbr.gov.au/fungi/images-misc/mycelium/mycelium2g.gif

Dying rear of

fungal colony

From: The Biology of Fungi, Ingold CT

Fairy rings - Marasmius oreades

http://www.lawnscience.co.uk/lawn-issues/fairy-rings/

http://www.daviddarling.info/images/fairy_ring_in_field.jpg

http://www.k-state.edu/turf/images/problem-solver/off-color/dark/fairy-

ring/fairy_ring.jpg

Fungal reproductionFungi grow vegetatively (only hyphae) as long as

nutrients available – Assimilative mode

When food runs out, fungus switches to

reproductive mode – produces spores.

Outer edge of colony – fresh substrate (1)

Centre, older regions of the mycelium (2) substrate

nutrients exhausted

→ growth ceases

→ Existing components used to

produce spores

→ Hyphae die (autolysis)

1

2

Image E. Bourguignon LU

Fungal reproduction

1. Almost all fungi produce SPORES on special

hyphal branches

2) Most fungi produce both an ASEXUAL and a

SEXUAL spore type

3) There is a great variety of forms in spores and

spore-bearing structures – basis of classification

From: The Biology of Fungi, Ingold CT

(from Plant Pathology, Agrios)

Spore structure

1. Most spores have:-

• Multilayered wall, often impregnated with

pigments and lipids

• Cytoplasm with a low water content &

high storage materials e.g. lipids,

glycogen, trehalose

• Little internal differentiation

• Low metabolic rate

BIOS-110 Fungal Biology

Lecture 3 - Fungal nutrition, growth and

reproduction

• Describe the features of a typical mycelial colony and how this relates to what we know about how fungi grow

• Outline the two ways in which yeast cells divide

• Define heterotrophic nutrition and describe how fungi obtain their nutrition

• Describe how a fairy ring is formed (structure and nutrition of the fairy ring fungus).

• Outline the different functions of spores.

• Outline the different spore dispersal mechanisms.