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)