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FUNGI FUNGI FUNGI FUNGI ----

STRUCTURES, FUNCTION STRUCTURES, FUNCTION STRUCTURES, FUNCTION STRUCTURES, FUNCTION

& METABOLISM& METABOLISM& METABOLISM& METABOLISM

Prof. S. S. Taiwo

LECTURE OUTLINELECTURE OUTLINELECTURE OUTLINELECTURE OUTLINE

� Introduction

� General characteristics of fungi

� Fungi cell structure (morphology)

� Gross morphology

� Ultrastructure

� Fungi reproduction

� Fungi metabolism and nutrition

INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION

� Fungi belong to the Kingdom Eukarya (along with Protista,

Plantae and Animalia)

� Whitaker 5- kingdom system of classification (1969)

INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION

� Are are heterotrophs that acquire nutrients by absorption

� Secrete hydrolytic enzymes and acids to decompose complex

molecules into simpler ones that can be absorbed

� Mostly saprophytic (soil) – food spoilage & contaminants

� Mutualistic (symbiotic) fungi - absorb nutrients from a host, but

reciprocate to benefit the host

� Parasitic - absorb nutrients from cells of living hosts;

� Opportunistic pathogen

� Non-opportunistic pathogen

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INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION� Fungi may be useful

� in industries –metabolic activities, particularly yeasts, are used in many

industrial fermentation processes (beer, wine, cheese, bread)

� used in other products – Citric acid in Coke is produced by Aspergillus

� used to produce antibiotics and other drugs

� Penicillium - Penicillin

� Streptomyces - Streptomycin

� Cephalosporium - Cephalosporin

� Cyclosporium - Cyclospora

INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION

� Pathogenic fungi

� About 100,000 species of fungi are known (>1.5m exist)

� Human pathogenic species (only 100). Associated diseases are rising due

to nosocomial infections and immunocompromised patients (i.e. HIV,

diabetes, transplant recipients etc)

� Aspergillosis, Blastomycosis—pulmonary infections and dissemination

may be involved.

� Plant pathogens (about 5,000) costs $1 billion/yr

INTRODUCTION…….INTRODUCTION…….INTRODUCTION…….INTRODUCTION…….

� Mycology

� study of fungi

� Mycologists

� scientists who study fungi

� Mycotoxicology

� study of fungal toxins and their effects

� Mycoses

� diseases caused by fungi

CHARACTERISTICS OF FUNGICHARACTERISTICS OF FUNGICHARACTERISTICS OF FUNGICHARACTERISTICS OF FUNGI

A. eukaryotic, non- vascular organisms

B. reproduce by means of spores (conidia), usually wind-

disseminated

C. both sexual (meiotic) and asexual (mitotic) spores may be

produced, depending on the species and conditions

D. typically not motile, although a few (e.g. Chytrids) have a motile

phase.

E. like plants, may have a stable haploid & diploid states

F. vegetative body may be unicellular (yeasts) or multicellular

moulds composed of microscopic threads called hyphae.

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CHARACTERISTICS………CHARACTERISTICS………CHARACTERISTICS………CHARACTERISTICS………

G. cell walls composed of mostly of chitinchitinchitinchitin and glucanglucanglucanglucan.

H. complex cytoplasm with internal organelles, microfilaments and

microtubules

I. fungi are heterotrophic (“other feeding,” must feed on preformed

organic material), not autotrophic (“self feeding,” make their

own food by photosynthesis).

- unlike animals (also heterotrophic), which ingest then digest,

fungi digest then ingest.

- fungi produce exo-enzymes to accomplish this

J. most fungi store their food as glycogen (like animals). Plants

store food as starch.

K. fungal cell membranes have a unique sterol, ergosterol,ergosterol,ergosterol,ergosterol, which

replaces cholesterol found in mammalian cell membranes

L. tubule protein—production of a different type in microtubules

formed during nuclear division.

M. most fungi have very small nuclei, with little repetitive DNA.

N. mitosis is generally accomplished without dissolution of the

nuclear envelope

CHARACTERISTICS………CHARACTERISTICS………CHARACTERISTICS………CHARACTERISTICS………

STRUCTURES OF FUNGI STRUCTURES OF FUNGI STRUCTURES OF FUNGI STRUCTURES OF FUNGI 1. Gross1. Gross1. Gross1. Gross morphologic structuremorphologic structuremorphologic structuremorphologic structure

Molds (filamentous fungi)

hypha (pl. hyphae)

may be coenocytic (no cross walls) or have septa (cross

walls)

mycelium (pl. mycelia)

bundles or tangled masses of hyphae

Yeast (unicellular fungi)

reproduce asexually, often by budding

reproduce sexually by formation of spores

MOLDSMOLDSMOLDSMOLDS

� Filamentous fungi

� hypha (pl. hyphae)

�may be coenocytic (no cross walls) or have septa (cross

walls)

� mycelium (pl. mycelia)

�bundles or tangled

masses of hyphae

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HyphaeHyphaeHyphaeHyphae

� Hyphae are designed to increase the surface area of fungi and

thus facilitate absorption

� May grow fast, up to 1 km per day, as they spread throughout a

food source

� May be coenocytic, having no septa between cells, or septa may

be present with pores through which cytoplasm can flow moving

nutrients through out the fungus

� Parasitic fungi have modified hyphae called haustoria, which

penetrate the host tissue but remain outside cell membrane

HyphaeHyphaeHyphaeHyphaeHyphaeHyphaeHyphaeHyphae

SeptaSeptaSeptaSepta

CoenocyticCoenocyticCoenocyticCoenocytic

PoresPoresPoresPores

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MyceliumMyceliumMyceliumMycelium

� Intertwined filamentous mass formed by hyphae, visible to the

unaided eye

� Forms when environmental conditions are right

� Vegetative mycelium: mycelial portion remaining INSIDE the substrate to

obtain nutrition

� Reproductive mycelium: mycelial portion extends into air, responsible for

SPORE reproduction

myceliamyceliamyceliamycelia

hyphahyphahyphahypha

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YEASTYEASTYEASTYEAST

� Unicellular, round or oval, size 8-15 x 3-5 µm

� Conidiogenesis (budding, binary fission, sexual spores)

Budding Budding Budding Budding

yeastsyeastsyeastsyeasts

Binary fissionBinary fissionBinary fissionBinary fission

DIMORPHIC FUNGI DIMORPHIC FUNGI DIMORPHIC FUNGI DIMORPHIC FUNGI

Thermally dimorphic fungi

Environment/Routine culture media

(SDA) 25-300C ---Mold form

Tissue/Enriched media (BHI)

35-370C---Yeast form

Sporothrix schenckii

2222. Fungi . Fungi . Fungi . Fungi

UltrastructureUltrastructureUltrastructureUltrastructure� Cell wall

� Plasma membrane

� Microtubules

� Nucleus

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Fungal wallFungal wallFungal wallFungal wall

� Shape of fungi

� Protect against osmotic lysis

� The wall contains pigments (melanin) � protect the cell

against ultraviolet radiation or the lytic enzymes of other

organisms

� Possess antigenic properties

Cell wall componentsCell wall componentsCell wall componentsCell wall components

� Predominance of polysaccharides, lesser amounts of

proteins and lipids

Cell wallCell wallCell wallCell wall componentscomponentscomponentscomponents

� The major polysaccharides of cell wall matrix consist of

glucans such as mannans, chitosan, and galactans

� Glucan refers to a group of D-glucose polymers having

glycosidic bonds (mannose, glucosamine , galactose)

� Insoluble β-glucans are apparently amorphous in cell wall

� Mannans, galactomannans, rhamnomannans are responsible

for the immunologic response to the medically important

yeasts and molds

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Cell wall componentsCell wall componentsCell wall componentsCell wall components� Another major component consists of chitinous

microfibrils embedded in the matrix of small

polysaccharides, proteins, lipids, inorganic salts & pigments

� Chitin is a (β1-4)-linked polymer of N-acetyl-D-glucosamine

(GlcNAc)

� Produced in cytosol (from UDP GlcNAc into chains of chitin

by chitin synthetase)

� The chitin microfibrils are transported to the plasmalemma and

subsequently integrated into the new cell wall

Major polysaccharide components of fungal wallsMajor polysaccharide components of fungal wallsMajor polysaccharide components of fungal wallsMajor polysaccharide components of fungal walls

DivisionDivisionDivisionDivision Fibrillar componentsFibrillar componentsFibrillar componentsFibrillar components Matrix componentsMatrix componentsMatrix componentsMatrix components

ChytridomycotaChytridomycotaChytridomycotaChytridomycota

ZygomycotaZygomycotaZygomycotaZygomycota

Ascomycota/DeuteromycotaAscomycota/DeuteromycotaAscomycota/DeuteromycotaAscomycota/Deuteromycota

BasidiomycotaBasidiomycotaBasidiomycotaBasidiomycota

Chitin, Glucan

Chitin, Chitosan

Chitin, β-(1,3)- & β-(1,6)-

glucans

Chitin, β-(1,3)- & β-(1,6)-

glucans

Glucan

Polyglucuronic acid,

glucuronomannoproteins

α-(1,3)-glucan,

galactomannoproteins

Chitin Chitin Chitin Chitin (N(N(N(N----AcetylAcetylAcetylAcetyl----1111----4444----β----DDDD---- glucosamine)glucosamine)glucosamine)glucosamine)

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Cellulose Cellulose Cellulose Cellulose ---- each each each each sugar is a glucose.sugar is a glucose.sugar is a glucose.sugar is a glucose.Peptidoglycan (without the connecting peptides).Peptidoglycan (without the connecting peptides).Peptidoglycan (without the connecting peptides).Peptidoglycan (without the connecting peptides).

Two different sugars alternatingTwo different sugars alternatingTwo different sugars alternatingTwo different sugars alternating

Peptidoglycan in bacteria and Cellulose in plantPeptidoglycan in bacteria and Cellulose in plantPeptidoglycan in bacteria and Cellulose in plantPeptidoglycan in bacteria and Cellulose in plantCell wall componentsCell wall componentsCell wall componentsCell wall components

� In addition to chitin, glucan, and mannan, cell walls may

contain lipid, protein, acid phosphatase, amylase, protease,

melanin, and inorganic ions (phosphorus, calcium, and

magnesium)

� The outer cell wall of dermatophytes contains

glycopeptides that may evoke both immediate and delayed

cutaneous hypersensitivity

Plasma membranePlasma membranePlasma membranePlasma membrane

� Similar to mammalian plasma membrane, differing in

having the non polar sterol, ergosterolergosterolergosterolergosterol, rather than

cholesterol

� Regulates the passage of materials into and out of the cell

by being selectively permeable

� Several antifungal agents interfere with ergosterol

synthesis (i.e., amphotericin B)

Fungal plasma membraneFungal plasma membraneFungal plasma membraneFungal plasma membrane

�The main role of the plasma membrane

� To regulate the uptake and release of materials

� Integral membrane protein (chitin syntase, glucan

syntase)

� Signal transduction

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Fungal microtubulesFungal microtubulesFungal microtubulesFungal microtubules

� Composed of the protein tubulin, which consists of a

dimer composed of two protein subunits.

� Microtubules are long, hollow cylinders ~ 25 nm in

diameter

� Involved in the movement of organelles, chromosomes,

nuclei, and Golgi vesicle containing cell wall precursor

Microtubules Microtubules Microtubules Microtubules

� Assist in the movement of chromosomes during mitosis

and meiosis

� The destruction of cytoplasmic microtubules interferes

with the transport of secretory materials to the cell

periphery, which may inhibit cell wall synthesis

Fungal nucleusFungal nucleusFungal nucleusFungal nucleus

� The nucleus is bounded by a double nuclear envelope and

contains chromatin and a nucleolus

� Fungal nuclei are variable in size, shape, and number

� The number of chromosomes varies with the particular

fungus

� Saccharomyces cerevisae ; 18 (n)

� Trichophyton mentagrophytes ; 4 (n)

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FUNGI REPRODUCTIONFUNGI REPRODUCTIONFUNGI REPRODUCTIONFUNGI REPRODUCTION

� Fungi are usually unicellular, haploidhaploidhaploidhaploid and of various

shapes and sizes

� Reproduce either sexually (by meiosis) or asexually (by

mitosis)

� In favourable conditions, fungi generally clone themselves

by producing enormous numbers of spores asexually

� For many fungi, sexual reproduction only occurs as a

contingency - results in greater genetic diversity

Sexual reproduction in fungiSexual reproduction in fungiSexual reproduction in fungiSexual reproduction in fungiFungi spend most of their life cycle as haploids.

Fertilization is followed immediately by meiosis, so the

diploid stage is just one cell.

This is the opposite of animals like humans: who are

diploid most of their life cycle, and are only haploid for the

1 cell gamete stage.

Most plants are similar to humans; diploid except for a

very short haploid phase

Asexual reproduction in fungiAsexual reproduction in fungiAsexual reproduction in fungiAsexual reproduction in fungi

All fungi produce asexual spores: this is the main way fungi

reproduce. There can be more than one type of asexual spore

produced at different stages of the life cycle, especially in the

rusts.

Like all eukaryotes, sexual reproduction is common in the fungi,

but not all do it. Some species have never been seen to

reproduce sexually. They are called imperfect fungi.imperfect fungi.imperfect fungi.imperfect fungi.

Asexual reproduction in fungi…..Asexual reproduction in fungi…..Asexual reproduction in fungi…..Asexual reproduction in fungi…..

� Spores are the agent of dispersal responsible for

geographic distribution of fungi:

� Carried by wind or water

� Germinate in moist places with appropriate

substrata

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Generalized life cycle of fungiGeneralized life cycle of fungiGeneralized life cycle of fungiGeneralized life cycle of fungi

SexualSexual

AsexualAsexual

Reproduction in YeastReproduction in YeastReproduction in YeastReproduction in YeastSacarrhomyces cerevisaeSacarrhomyces cerevisaeSacarrhomyces cerevisaeSacarrhomyces cerevisae� Sacarrhomyces cerevisiae is usually haploid, but after it mates it can live as

a stable diploid for many generations.

� The mating types are called a and α (alpha). Each secretes a pheromone that attracts

the other.

� The diploid cell undergoes meiosis to produce 4 haploid cells.

Reproduction in MoldsReproduction in MoldsReproduction in MoldsReproduction in Molds

Ascomycetes e.g. Ascomycetes e.g. Ascomycetes e.g. Ascomycetes e.g. AspergillusAspergillusAspergillusAspergillus spspspsp

Ascomycetes are septate: the hyphae are divided into

separate cells. This is the opposite of coenocytic (which is

what zygomycetes are).

When cells of opposite mating types meet, they form

dikaryon dikaryon dikaryon dikaryon hyphae.

Ascomycete hyphae can grow quite large, and for a long time,

as dikaryons i. e. plasmogamy plasmogamy plasmogamy plasmogamy occurs long before karyogamykaryogamykaryogamykaryogamy

Reproduction in Molds…….Reproduction in Molds…….Reproduction in Molds…….Reproduction in Molds…….The dikaryon forms a fruiting body (e.g. the truffle or morel)

made of hyphae. At the tips of each hypha in the fruiting body,

the ascus (sac) forms. In the ascus cell, the two haploid nuclei

fuse to form a diploid, which then undergoes meiosis.

The 4 haploid cells from meiosis often form a nice line; in some

species each nucleus divides to form a total of 8 haploid cells

(geneticists love this).

The haploid nuclei are then packaged into sexual spores, which

can resist harsh conditions, and expelled from the fruiting body.

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Reproduction in MoldsReproduction in MoldsReproduction in MoldsReproduction in MoldsAscomycetesAscomycetesAscomycetesAscomycetes PHYSIOLOGY OF FUNGIPHYSIOLOGY OF FUNGIPHYSIOLOGY OF FUNGIPHYSIOLOGY OF FUNGI

�Energy metabolism

�Nutrition

�Water

�Temperature

�Hydrogen ion (pH)

� Light

Energy metabolism of fungiEnergy metabolism of fungiEnergy metabolism of fungiEnergy metabolism of fungi

� The fungi include species that are obligately aerobic (e.g.

most Zygomycota), obligately anaerobic (eg. rumen fungi)

� Organisms can obtain energy by oxidative (respiratory)

metabolism or by fermentation

� O2 is used for oxidative metabolism to generate energy,

However it is essential for biosynthesis of sterols,

unsaturated fatty acids and some vitamins

Energy metabolism in relation to OEnergy metabolism in relation to OEnergy metabolism in relation to OEnergy metabolism in relation to O2 2 2 2 requirementsrequirementsrequirementsrequirements

Obligately oxidative (Obligate aerobes) e.g. Rhodotorulla

Facultatively fermentative. Energy can be obtained by oxidative and

fermentative processes such fungi are likely to be facultative

anaerobes. Oxidative metabolism, provides much more energy

than fermentative, so higher yields can occur under aerobic

conditions. e.g. Mucor, Saccharomyces

Obligately fermentative. Oxygen is not needed for energy

production, may be either harmless or toxic. e.g. Blastocladia,

Neocallimastix

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Absorptive modeAbsorptive modeAbsorptive modeAbsorptive mode

Over whole surface or via restricted absorbing regions e.g.

a. rhizoids in "lower" fungi

b. substrate hyphae* in "higher" fungi

c. apical tips of hyphae

*The substrate hyphae of molds nourish the aerial hyphae and reproductive

hyphae

Extracellular Extracellular Extracellular Extracellular digestiondigestiondigestiondigestion

Fungi secrete enzymes that depolymerize complex natural products (proteins,

carbohydrates, lipids, etc.) so they can be absorbed as sources of carbon and

energy

Fungi nutritionFungi nutritionFungi nutritionFungi nutrition

Nutrient requirements of fungiNutrient requirements of fungiNutrient requirements of fungiNutrient requirements of fungi

�CarbonCarbonCarbonCarbon needs for the synthesis of carbohydrates,

lipids, nucleic acids, and proteins.

� Simple sugars, polysaccharides, citric acid, glycerol

�NitrogenNitrogenNitrogenNitrogen for synthesis of amino acids for proteins,

purines and pyrimidines for nucleic acids,

glucosamine for chitin, and various vitamins

�Amino acid, ammonium, nitrate

Nutrient requirements of fungiNutrient requirements of fungiNutrient requirements of fungiNutrient requirements of fungi …….…….…….…….� C/N ratio (20:1)

� Other elements

� P: energy-rich compound metabolism, phospholipid in lipid

bilayer

� K: coenzyme

� Mg: concern with sporulation

� S: protein component

� Trace elements

� Fe, Cu, Mn & Zn

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Nutrient requirements of fungiNutrient requirements of fungiNutrient requirements of fungiNutrient requirements of fungi …….…….…….…….CzapekCzapekCzapekCzapek----DoxDoxDoxDox (CD) medium(CD) medium(CD) medium(CD) medium

widely used for the culture of fungiwidely used for the culture of fungiwidely used for the culture of fungiwidely used for the culture of fungi

Mineral base:

C and energy source:

N source:

Water:

If a solid medium is required:

KH2PO4

MgSO4.7H2O

KCl

FeSO4.7H2O

Sucrose (Glu, starch)

NaNO3

Agar

1 g

0.5 g

0.5 g

0.01 g

30 g

2 g

1 litre

20 g

Water requirement by fungiWater requirement by fungiWater requirement by fungiWater requirement by fungi

� Most fungi require very high water availability (relative

humidity), and rapidly dry out or senescence in dry

conditions.

� Water activity (aw) = ps/pw (pure water = 1)

� DNA is denatured at aw = 0.55

� Osmophiles 0.85, Xerophiles 0.80, Halophiles 0.75

� The xerotolerant fungi can grow slowly, at water activity of 0.64

Temperature requirement by fungiTemperature requirement by fungiTemperature requirement by fungiTemperature requirement by fungi

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pH requirement for fungipH requirement for fungipH requirement for fungipH requirement for fungi

�Optimum pH 5.0-7.0

�Acid-tolerant (pH 2.0)� Aspergillus, Penicillium,

Fusarium, yeast in stomach of animals

� Strongly alkaline environment (pH 10-11) �

Fusarium oxysporum, P. variabile

Light requirement for fungiLight requirement for fungiLight requirement for fungiLight requirement for fungi

� Light has influence on fungal growth in specific

cases

� Light does not play a major part in growth and

metabolism of fungi

�A common metabolic effect of light is the induction

of carotenoid biosynthesis