Transcript Lecture 9-Mycology

Kingdom Fungi
Introduction
Prof. Khaled Abu-Elteen
Objectives
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Introduction of fungi
Biology of fungi
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Physiology of fungi
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Cell structure, growth and development
Nutrition, Temp, UV light, and water
Classification of fungi
Some terms
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mycology
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mycologists
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scientists who study fungi
mycotoxicology
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study of fungi
study of fungal toxins and their effects
mycoses
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diseases caused by fungi
FUNGI
100,000 species
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
Fungal Characteristics
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Eukaryotic
Multicellular
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
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Eukaryotic, Heterotrophic
(chemoheterotrophic) microorganism
No chlorophyll, non-motile
Thread of cells (hyphae), transverse cell
walls (septate), hyphal anastomosis
Storage compound; glycogen
Molds
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filamentous fungi
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hyphae (s., hypha)
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the filaments of a mold
may be coenocytic (no cross walls) or have septa
(cross walls)
mycelium (pl. mycelia)
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bundles or tangled masses of hyphae
Yeasts
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unicellular fungi
reproduce asexually, often by budding
reproduce sexually by formation of spores
Hyphae
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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
Pores
Septa
Coenocytic
The Body of a Fungus
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Fungi exist mainly in the form of slender
filaments (hyphae).
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long chains of cells joined end-to-end divided by
cross-walls (septa)
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rarely form complete barrier
cytoplasm freely streams in hyphae
mycelium - mass of connected hyphae
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grows through and penetrates substrate
MYCELIUM
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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
Introduction of fungi
Other characteristics of fungi
 the ability to synthesize lysine by the -amino
adipic acid pathway (AAA-pathway)
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possession of a chitinous cell wall
plasma membranes containing the sterol
ergosterol
and microtubules composed of tubulin.
Structure
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Cell wall
Plasma membrane
Microtubules
Nucleus
Fungal wall
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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
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Predominance of polysaccharides, lesser
amounts of proteins and lipids
Table 1 Major polysaccharide components of
fungal walls
Division
Fibrillar components Matrix components
Chytridiomycota Chitin, glucan
Glucan
Zygomycota
Chitin, chitosan
Polyglucoronic acid,
glucuronomannoproteins
Ascomycota/
Chitin, (1,3)-(1,6)deuteromycota glucans
Basidiomycota Chitin, (1,3)- (1,6)glucans
-(1,3)-Glucan, galactomannoproteins ,,
Cell wall components
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The major polysaccharides of cell wall matrix
consist of glucans such as manans, chitosan,
and galactans
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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
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Consisting of chitinous microfibrils embedded in
the matrix of small polysaccharides, proteins,
lipids, inorganic salts, and pigments
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Chitin is a (1-4)-linked polymer of N-acetyl-Dglucosamine (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
Cell wall components
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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
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The main role of the plasma membrane
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To regulate the uptake and release of materials
Integral membrane protein (chitin syntase,
glucan syntase)
Signal transduction
Plasma membrane
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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
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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
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Assist in the movement of chromosomes
during mitosis and meiosis
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the destruction of cytoplasmic microtubules
interferes with the transport of secretory
materials to the cell periphery, which may
inhibit cell wall synthesis
Nucleus
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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
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S.cerevisiae ; 18 (n)
T.mentagophytes ; 4 (n)
The growth of hyphae
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Apical extension
Balance between wall
synthesis and wall lysis
The apical vesicles are
produced from Golgi
bodies and then
transported to the tip
Spitzenkörper (apical body)
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The vesicles fuse with the plasma membrane at the tip,
and release their contents.
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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
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Aeration
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The fungi include species that are obligately
aerobic (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
The nutrient requirement of fungi
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Carbon needs for the synthesis of
carbohydrates, lipids, nucleic acids, and
proteins.
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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
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Amino acid, ammonium, nitrate
Nutrition
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C/N ratio (20:1)
Other elements
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P : energy-rich compound metabolism,
phospholipid in lipid bilayer
K : coenzyme
Mg : concer with sporulation
S : protein component
Trace elements
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Fe, Cu, Mn, and Zn
Nutrition
Czapek-Dox medium
widely used for the culture of fungi
Mineral base:
C and energy source:
KH2PO4
MgSO4.7H2O
KCl
FeSO4.7H2O
Sucrose (Glu,starch)
N source:
Water:
NaNO3
If a solid medium is
required:
Agar
1g
0.5 g
0.5 g
0.01 g
30 g
2g
1 litre
20 g
Water availability
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Most fungi require very high water availability
(relative humidity), and rapidly dry out or
senescence in dry conditions.
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Water activity (aw) = ps/pw
(pure water = 1)
DNA is denatured at aw = 0.55
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Osmophiles 0.85, Xerophiles 0.80, Halophiles 0.75
The xerotolerant fungi can grow slowly, at water
activity of 0.64.
Temperature
Hydrogen ion
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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
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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
Morphology
Yeast
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Unicellular, round or oval, size 8-15 x 3-5 µm
Conidiogenesis (budding, binary fission, sexual
spores)
Budding
yeasts
Binary fission
Morphology
Mold
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Multicellular, hyphae, septate & nonseptate,
hyaline & dematiaceous, diameter 4-20 µm
Sexual and asexual reproduction
Hyaline septate hyphae
Dematiaceous septate hyphae
Hyaline aseptate hyphae
Morphology
Dimorphic fungi (thermally dimorphic fungi)
Environment/Routine culture media
(SDA) 25-300C ---Mold form
Sporothrix schenckii
Tissue/Enriched media (BHI)
35-370C---Yeast form
Morphology
For example, the dimorphic fungus
Blastomyces dermatitidis
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Anamorph : hyphae, conidia at 250C and
budding yeast cell at 370C
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The name B.dermatitidis summarizes these two
anamorphs
Teleomorph : sexual fruiting body, called a
gymnothecium, containing ascospores
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The name that is used for this sexual form or
teleomorph is Ajellomyces dermatitidis
Sexual reproduction
Gametes or
gametic nuclei (n)
n (haploid)
Meiosis
n (monokaryon)
Plasmogamy (cell fusion)
n+n (dikaryon)
2n (diploid)
Zygote (2n)
Karyogamy
(nuclear fusion)
Division Ascomycota
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Common name: Sac fungi
Sexual reproduction: ascospore in ascus
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Asci may form in fruiting body called an ascocarp
Gymnothecium, Cleistothecium, Perithecium, Apothecium
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Asexual reproduction: conidia, arthospore,
budding
septate hyphae or yeast
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Eurotium (Aspergillus)., Arthroderma (Trichophyton)
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Life cycle of ascomycetes
Arthospore
Cleistothecium
Ascocarp
Gymnothecium
Perithecium
Apothecium
Life cycle of the yeast
Saccharomyces cerevisiae
a
c
b
Division Basidiomycota
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Common name: Club fungi, mushroom
Sexual reproduction: basidiospore
Asexual reproduction:budding
hyphae with dolipore septum or yeast
clamp connection
Mushroom: basidiocarp, fruiting body
Filobasidiella neoformans (no basidiocarp) or
Crytococcus neoformans
Clamp connection
Life cycle of basidiomycetes
Amanita phalloides
Division: Zygomycota
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Common name: Bread molds
Sexual reproduction: Zygospore
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Mating type +, mating type -
Asexual reproduction: Sporangiospore,
sporangium
coenocytic hyphae (aseptate hyphae)
Rhizopus sp., Mucor sp., Asidia sp.
Life cycle of Rhizopus stolonifer
Division: Chytidiomycota
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Common name: Water molds
Sexual reproduction: Oospore
Asexual reproduction: Zoospore,
zoosporangium, flagella
aseptate hyphae
Phythium insidiosum
Deuteromycota
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Common name: Imperfect fungi
have no known sexual state in life cycle
Asexual reproduction : conidia (blastic,
thallic)
septate hyphae or yeast
Human pathogenic fungi: dermatophytes,
dimorphic fungi
Conidiogenesis
Blastic: the conidium originate from a narrow portion of the region
which swells before being cut off by a septum
Phialophora
Cladosporium
Curvularia
Penicillium
Scopulariopsis
Blastic conidiogenesis
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Acropetal conidia
Sympodia condia
Poroconidia
Phialoconidia
Anneloconidia
Conidiogenesis
Thallic: the conidium arise from a broad zone of the region and
septa laid down before the conidium swells
Candida albicans
Geotrichum
Microsporum
Trichophyton
Thallic conidiogenesis
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Arthoconidia
Thallic solitary conidia
Chlamydoconidia (chlamydosprore)