Kingdom FungiIntroduction

Prof. Khaled Abu-Elteen

Objectives Introduction of fungi Biology of fungi

Cell structure, growth and development

Physiology of fungi Nutrition, Temp, UV light, and water

Classification of fungi

Some terms mycology

study of fungi mycologists

scientists who study fungi mycotoxicology

study of fungal toxins and their effects mycoses

diseases caused by fungi

•100,000 species•Only 100 human pathogens, fungi associated diseases are rising, due to nosocomial infections and in immunocompromised patients (ie. HIV, diabetes, transplant folks)•Aspergillosis, Blastomycosis—pulmonary infections and dissemination may be involved.•5,000 plant pathogens=$1 billion/yr

FUNGI

Fungal Characteristics Eukaryotic Most are Multicellular and some are unicellular. Heterotrophic Absorb nutrients - may be saprobes (absorb from dead

material), parasites, or mutualistic symbionts (with algae make lichen).

Secrete powerful hydrolytic enzymes. Cell walls contain chitin, an amino sugar polysaccharide

also found in arthropod exoskeletons Lack flagella

Characteristics 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.

G. cell walls composed of mostly of chitin and glucan.

H. Complex cytoplasm with internal organelles, microfilaments and microtubules

H. 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 exoenzymes to accomplish this

I. Most fungi store their food as glycogen (like animals). Plants store food as starch.

K. Fungal cell membranes have a unique sterol, 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

Introduction of fungi Eukaryotic, Heterotrophic

(chemoheterotrophic) microorganism No chlorophyll, non-motile Thread of cells (hyphae), transverse cell

walls (septate), hyphal anastomosis Storage compound; glycogen

Molds filamentous fungi

hyphae (s., hypha) the filaments of a mold may be coenocytic (no cross walls) or have septa

(cross walls) mycelium (pl. mycelia)

bundles or tangled masses of hyphae

Yeasts unicellular fungi reproduce asexually, often by budding reproduce sexually by formation of spores

Hyphae

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

Hyphae

Hyphae

Septa

Coenocytic

Pores

The Body of a Fungus Fungi exist mainly in the form of slender

filaments (hyphae). long chains of cells joined end-to-end divided by

cross-walls (septa) rarely form complete barrier cytoplasm freely streams in hyphae

mycelium - mass of connected hyphae grows through and penetrates substrate

MYCELIUM

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

mycelia

hypha

Introduction of fungiOther characteristics of fungi the ability to synthesize lysine by the -amino

adipic acid pathway (AAA-pathway) possession of a chitinous cell wall plasma membranes containing the sterol

ergosterol and microtubules composed of tubulin.

Structure Cell wall Plasma membrane Microtubules Nucleus

Fungal wall Shape of fungi Protect against osmotic lysis It the wall contains pigments (melanin)

protect the cell against ultraviolet radiation or the lytic enzymes of other organisms

It can have antigenic properties

Cell wall components Predominance of polysaccharides, lesser

amounts of proteins and lipids

Table 1 Major polysaccharide components of fungal walls

Division

Chytridiomycota

Zygomycota

Ascomycota/

deuteromycota

Basidiomycota

Fibrillar components

Chitin, glucan

Chitin, chitosan

Chitin, (1,3)-(1,6)-

glucans

Chitin, (1,3)- (1,6)-

glucans

Matrix components

Glucan

Polyglucoronic acid, glucuronomannoproteins

-(1,3)-Glucan, galacto-

mannoproteins ,,

Chitin ( N-Acetyl-1-4-β-D- glucosamine

Cell wall components The major polysaccharides of cell wall matrix

consist of glucans such as manans, chitosan, and galactans Glucan refers to a group of D-glucose polymers

having glycosidic bonds Insoluble -glucans are apparently amorphous in cell

wall Mannans, galactomannans, rhamnomannans are

responsible for the immunologic response to the medically important yeasts and molds

Cell Wall Structure In Fungi

Cell wall components Consisting of chitinous microfibrils embedded in

the matrix of small polysaccharides, proteins, lipids, inorganic salts, and pigments Chitin is a (1-4)-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

Monosaccharides with taxon association

D-galactose (Ascomycota) D-galactosamine ( Ascomycota )

L-fucose (Mucorales & Basidiomycota)D-glucosamine (Mucorales) D-xylose (Basidiomycota) Uronic acids (Mucorales)

D-rhamnose (Ascomycota)*

*somewhat rare

Cell wall components In addition to chitin, glucan, and mannan, cell

walls may contain lipid, protein, chitosan, 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 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

Plasma membrane Similar to mammalian plasma membrane,

differing in having the nonpolar sterol ergosterol, rather than cholesterol

regulates the passage of materials into and out of the cell by being selective permeable

Several antifungal agents interfere with ergosterol synthesis (i.e., amphotericin B)

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 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

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 S.cerevisiae ; 18 (n) T.mentagophytes ; 4 (n)

The growth of hyphae Apical extension Balance between wall

synthesis and wall lysis The apical vesicles are p

roduced from Golgi bodies and then transported to the tip

Spitzenkörper (apical body)

The vesicles fuse with the plasma membrane at the tip, and release their contents. enzymes involved in wall synthesis, (chitin syntase,

glucan synthase) enzymes involved in wall lysis, enzyme activators, some preformed wall polymers such as mannoproteins

Physiology Aeration Nutrition Water Temperature Hydrogen ion Light

Aeration The fungi include species that are obligately aer

obic (eg. 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

Table 2 Energy metabolism in relation to O2 requirements

Obligately oxidative. Obligate aerobes. Exp. Rhodotorula

Facultatively fermentative. Energy can be obtained by oxidative and fermentative processed such fungi are likely to be faculative anaerobes. Oxidative metabolism, provides much more energy than fermentative, so higher yields can occur under aerobic conditions. Exp. Mucor, Saccharomyces

Obiligately fermentative. Oxygen is not needed for energy production , may be either harmless or toxic. Exp. Blastocladia, Neocallimastix

Diagrammatic representation of the mixed-acid fermentation of the rumen chytrid Neocallimastix. Part of the fermentation occurs in the cytosol and hydrogenosome

Hydrogenosome: functionally equivalent to the mitochondria of aerobic organisms

Fungal nutrition A. Absorptive 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 B. Extracellular digestion

Fungi secrete enzymes that depolymerize complex natural products (proteins, carbohydrates, lipids, etc.) so they can be absorbed as sources of carbon and energy.

rhizoids

Mycelia

The nutrient requirement of fungi Carbon needs for the synthesis of

carbohydrates, lipids, nucleic acids, and proteins. Simple sugars, polysaccharides, citric acid, glycerol

Nitrogen for synthesis of amino acids for proteins, purines and pyrimidines for nucleic acids, glucosamine for chitin, and various vitamins Amino acid, ammonium, nitrate

Nutrition C/N ratio (20:1) Other elements

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

K : coenzyme Mg : concer with sporulation S : protein component

Trace elements Fe, Cu, Mn, and Zn

Nutrition

Czapek-Dox medium widely 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 availability Most fungi require very high water availability (r

elative 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

Hydrogen ion Opt. pH 5.0-7.0 Acid-tolerant (pH 2.0) Aspergillus,

Penicillium, Fusarium, yeast in stomach of animals

Strongly alkaline environment (pH 10-11) F.oxysporum, P.variabile

Light Influence on fungal growth in specific cases light does not play a major part in growth an

d metabolism of fungi A common metabolic effect of light is the

induction of carotenoid biosynthesis

MorphologyYeast

Unicellular, round or oval, size 8-15 x 3-5 µm Conidiogenesis (budding, binary fission, sexual

spores)

Budding yeasts

Binary fission

MorphologyMold

Multicellular, hyphae, septate & nonseptate, hyaline & dematiaceous, diameter 4-20 µm

Sexual and asexual reproduction

Hyaline aseptate hyphae

Dematiaceous septate hyphae

Hyaline septate hyphae

Morphology

Dimorphic fungi (thermally dimorphic fungi)

Environment/Routine culture media (SDA) 25-300C ---Mold form

Tissue/Enriched media (BHI) 35-370C---Yeast form

Sporothrix schenckii

Morphology

CLASSIFICATION

Fungi are eukaryotic organisms that do not contain chlorophyll, but have cell walls,

filamentous structures, and produce spores. These organisms grow as saprophytes and

decompose dead organic matter. There are between 100,000 to 200,000 species depending on

how they are classified. About 300species are presently known to be pathogenic for man. There are five kingdoms of living things. The fungi are

in the Kingdom Fungi.

KINGDOM CHARACTERISTIC EXAMPLE Monera Prokaryocyte Bacteria Actinomycetes Protista Eukaryocyte Protozoa Fungi Eukaryocyte * Fungi Plantae Eukaryocyte Plants, Moss Animalia Eukaryocyte * Arthropods Mammals Man

*This common characteristic is responsible for the therapeutic dilemma in anti-mycotic

therapy.

Medically important fungi are in four phyla:

1. Ascomycota - Sexual reproduction in a sack called an ascus with the production of ascopspores.( Aspergillus, Blastomyces dermatidis, Histoplasma capsulatus)

2. Basidiomycota -Sexual reproduction in a sack called a basidium with the production of basidiospores.( Cryptococcus neoformans)

3. Zygomycota - sexual reproduction by gametes and asexual reproduction with the formation of zygospores.( Rhizopus, Mucor)

4. Deuteromycota(Fungi Imperfecti \Mitosporic Fungi) - no recognizable form of sexual reproduction. Includes most pathogenic fungi ( Sporothrix, Coccidioides immitis, Candida, Pneumocystis).