Taxonomy, biology and physiology of fungi

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Taxonomy, biology and physiology of fungi

• Course Advanced Clinical Microbiology (508701)
• Lecturer Kanya Preechasuth
• Clinical Microbiology, Faculty of AMS, CMU

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Objectives

• Introduction of fungi
• Biology of fungi
• Cell structure, growth and development
• Physiology of fungi
• Nutrition, Temp, UV light, and water
• Classification of fungi

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Introduction of fungi

• Eukaryotic, Heterotrophic (chemoheterotrophic)
  microorganism
• No chlorophyll, non-motile
• Thread of cells (hyphae), transverse cell walls
  (septate), hyphal anastomosis
• Storage compound glycogen

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Introduction of fungi

• Other 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.

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Structure

• Cell wall
• Plasma membrane
• Microtubules
• Nucleus

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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

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Cell wall components

• Predominance of polysaccharides, lesser amounts
  of proteins and lipids

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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 ,,
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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

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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

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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

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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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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)

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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

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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

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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)

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The growth of hyphae

• Apical extension
• Balance between wall synthesis and wall lysis
• The apical vesicles (Spitzenkörper) 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.
• enzymes involved in wall synthesis, (chitin
  syntase, glucan synthase)
• enzymes involved in wall lysis,
• enzyme activators,
• some preformed wall polymers such as mannoproteins

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Hyphal anastomosis

• Vegetative hyphal fusion in common in higher
  fungi
• Involves the growth of hyphae toward each other

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Physiology

• Aeration
• Nutrition
• Water
• Temperature
• Hydrogen ion
• Light

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Aeration

• 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

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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

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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
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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

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Nutrition

• C/N ratio (201)
• 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

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Nutrition
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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
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Water availability

• 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.

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Temperature
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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

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Light

• 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

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Morphology

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

Budding yeasts
Binary fission
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Morphology

• Mold
• Multicellular, hyphae, septate nonseptate,
  hyaline dematiaceous, diameter 4-20 µm
• Sexual and asexual reproduction

Hyaline septate hyphae
Dematiaceous septate hyphae
Hyaline aseptate hyphae
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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
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Morphology
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Classification of fungi

• Kingdom Fungi
• Division -mycota
• Subdivision -mycotina
• Class -mycetae
• Subclass -mycetes
• Order -ales
• Family -aceae
• Genus --------
• Species --------

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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)

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• 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

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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
  teleomorph is Ajellomyces dermatitidis

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Sexual reproduction
Gametes or gametic nuclei (n)
n (monokaryon)
n (haploid)
Plasmogamy (cell fusion)
Meiosis
nn (dikaryon)
2n (diploid)
Karyogamy (nuclear fusion)
Zygote (2n)
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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)

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Life cycle of ascomycetes
Arthospore
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Ascocarp
Cleistothecium
Gymnothecium
Perithecium
Apothecium
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Life cycle of the yeast Saccharomyces cerevisiae
a
c
b
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Division Basidiomycota

• Common name Club fungi, mushroom
• Sexual reproduction basidiospore
• Asexual reproductionbudding
• hyphae with dolipore septum or yeast
• clamp connection
• Mushroom basidiocarp, fruiting body
• Filobasidiella neoformans (no basidiocarp) or
  Crytococcus neoformans

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Clamp connection
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Life cycle of basidiomycetes
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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.

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Life cycle of Rhizopus stolonifer
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Division Chytidiomycota

• Common name Water molds
• Sexual reproduction Oospore
• Asexual reproduction Zoospore, zoosporangium,
  flagella
• aseptate hyphae
• Phythium insidiosum

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Deuteromycota

• 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

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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
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Blastic conidiogenesis

• Acropetal conidia
• Sympodia condia
• Poroconidia
• Phialoconidia
• Anneloconidia

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Conidiogenesis
Thallic the conidium arise from a broad zone of
the region and septa laid down
before the conidium swells
Candida albicans
Microsporum
Trichophyton
Geotrichum
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Thallic conidiogenesis

• Arthoconidia
• Thallic solitary conidia
• Chlamydoconidia (chlamydosprore)