Download - Taxonomy, biology and physiology of fungi
Taxonomy, biology and physiology of fungi
Objectives Introduction of fungi Biology of fungi
Cell structure, growth and development
Physiology of fungi Nutrition, Temp, UV light, and water
Classification of fungi
Introduction of fungi Eukaryotic, Heterotrophic
(chemoheterotrophic) microorganism No chlorophyll, non-motile Thread of cells (hyphae), transverse cell
walls (septate), hyphal anastomosis Storage compound; glycogen
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
Oomycota
Chytridiomycota
Zygomycota
Ascomycota/
deuteromycota
Basidiomycota
Fibrillar components
Cellulose, (1,3)-
(1,6)-glucans
Chitin, glucan
Chitin, chitosan
Chitin, (1,3)-(1,6)-
glucans
Chitin, (1,3)- (1,6)-
glucans
Matrix components
Glucan
Glucan
Polyglucoronic acid, glucuronomannoproteins
-(1,3)-Glucan, galacto-
mannoproteins
,,
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 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
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 (Spitz
enkörper) are produced 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
Hyphal anastomosis Vegetative hyphal fusion in common in
higher fungi Involves the growth of hyphae toward each
other
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
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 of fungi Kingdom Fungi Division -mycota Subdivision -mycotina Class -mycetae Subclass -mycetes Order -ales Family -aceae Genus -------- Species --------
Classification of fungi Four major division of fungi, base on the type of
sexual spores (ascospore, basidiospore, zygospore, oosore), plus another group, which have no know sexual state. Ascomycota Basidiomycota Zygomycota Chytridiomycota Deuteromycota (Imperfect fungi)
Sexual reproductive structures, which are referred to as teleomorphs reflect phylogenetic relationships because they
are based upon structures that form following meiosis
Asexual reproductive structures, which are referred to as anamorphs does not reflect phylogenetic relationships
For example, the dimorphic fungus Blastomyces dermatitidis
Anamorph : hyphae, conidia at 250C and budding yeast cell at 370C The name B.dermatitidis summarizes these two
anamorphs
Teleomorph : sexual fruiting body, called a gymnothecium, containing ascospores The name that is used for this sexual form or tele
omorph is Ajellomyces dermatitidis
Gametes or gametic nuclei (n)
Plasmogamy (cell fusion)
Karyogamy (nuclear fusion)
Zygote (2n)
Meiosis
n (monokaryon)
n+n (dikaryon)2n (diploid)
n (haploid)
Sexual reproduction
Division Ascomycota Common name: Sac fungi Sexual reproduction: ascospore in ascus
Asci may form in fruiting body called an ascocarp Gymnothecium, Cleistothecium, Perithecium, Apothecium
Asexual reproduction: conidia, arthospore, budding
septate hyphae or yeast Eurotium (Aspergillus)., Arthroderma (Trichophyton)
Arthospore
Life cycle of ascomycetes
Ascocarp
Perithecium
Apothecium
Cleistothecium
Gymnothecium
Life cycle of the yeast Saccharomyces cerevisiae
a
b
c
Division Basidiomycota 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 Cryt
ococcus neoformans
Clamp connection
Life cycle of basidiomycetes
Amanita phalloides
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Division: Zygomycota Common name: Bread molds Sexual reproduction: Zygospore
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 Common name: Water molds Sexual reproduction: Oospore Asexual reproduction: Zoospore, zoosporan
gium, flagella aseptate hyphae Phythium insidiosum
Deuteromycota Common name: Imperfect fungi have no known sexual state in life cycle Asexual reproduction : conidia (blastic, thall
ic) septate hyphae or yeast Human pathogenic fungi: dermatophytes, dimorphic fungi
CladosporiumPhialophora
Curvularia
ScopulariopsisPenicillium
Blastic: the conidium originate from a narrow portion of the region which swells before being cut off by a septum
Conidiogenesis
Blastic conidiogenesis Acropetal conidia Sympodia condia Poroconidia Phialoconidia Anneloconidia
ConidiogenesisThallic: the conidium arise from a broad zone of the region and septa laid down before the conidium swells
Candida albicans Microsporum
Geotrichum Trichophyton
Thallic conidiogenesis Arthoconidia Thallic solitary conidia Chlamydoconidia (chlamydosprore)