Basics of mycology

1. Basic Mycology

2. FUNGI
 More then 80,000 species of
fungi have been described
 About 400 are pathogenic to
humans and animals.
All fungi are chemoheterotrophs,
requiring organic compounds for
energy and carbon.
Fungi are aerobic or facultatively
anaerobic; only a few anaerobic
fungi are known.
Mycology: the study of fungi

3. Kingdom Fungi
Nutritional Type Chemoheterotroph
Multicellularity All, except yeasts
Cellular Arrangement
Unicellular, filamentous,
fleshy
Food Acquisition Method Absorptive
Characteristic Features Sexual and asexual spores
Fungi Classification

4. Fungi vs Bacteria

5.  Fungi have two basic growth forms - molds and yeasts.
 Growth in the mold form occurs by the production
of multicellular branching cylindrical tubules called hyphae
with diameter 2 -10 μm.
Hyphae are extended by apical elongation.
Mycelium is the mass of intertwined hyphae that accumulates
during active growth;
 Yeasts are single cells, with spherical to ellipsoid
Shape, diameter from 3 to 15 μm.
Most yeasts reproduce by budding, or some by biinary
fission
Yeasts and Molds

6.  Fungi have a rigid cell wall that determines their shape
- protects them from osmotic and other environmental stresses.
 Cell wall is composed largely of carbohydrate layers—long chains
of polysaccharides—as well as glycoproteins and lipids
- Main component- chitin is a polysaccharide composed of long
chains of N-acetylglucosamine.
- other polysaccharides :
glucans, a long polymer of D-glucose,
mannans, polymers of mannose.
- These components are cross-linked to form a multi-layered cell wall
matrix.
Fungal cell wall and cell membrane

7.  During the fungal infection the surface components of
the cell wall mediate attachment of the fungus to host
cells.
 Cell wall components stimulate innate immune
responses.
Glucans and other polysaccharides may activate the
complement cascade and provoke an inflammatory
reaction.
 Fungal cell membrane contains ergosterol, in
contrast to the human cell membrane, which
contains cholesterol.
- The selective action of amphotericin B and azole
drugs, on fungi is based on this difference in
membrane sterols
Fungal cell wall and cell membrane

8. Vegetative Growth
 Molds and Fleshy Fungi
 The fungal thallus (body) consists of hyphae; a
mass of hyphae is a mycelium
 Septate hyphae - hyphae contain cross-walls
called septa which divide them into distinct,
uninucleate cell-like units.
 Coenocytic hyphae - hyphae contain no septa -
long, continuous cells with many nuclei

9. Characteristics of fungal hyphae.
Septum
Cell wall
Pore
Nuclei
Septate hypha Coenocytic hypha Growth of a hypha from a spore
Spore

10. Vegetative Growth
• The portion of a hypha that obtains
nutrients is called the vegetative
hypha;
• the portion concerned with
reproduction is the reproductive
or aerial hypha
- it projects above the surface of
the medium on which the fungus
is growing.
• Aerial hyphae often bear reproductive
spores
Example of Mycelium
on petri dish

11. Aerial and vegetative hyphae.
Aerial hyphae
Aspergillus niger

12. • Unicellular fungi
Fission yeasts ( e.g.Schizosaccaromyces )divide
symmetrically
Budding yeasts divide asymmetrically
One yeast cell can in time produce up to 24 daughter
cells by budding.
Some yeasts (.e.g. Candida albicans) can produce buds that
form a short chain of cells called pseudohypha.
• Dimorphism
Pathogenic dimorphic fungi are yeast-like at 37°C and
mold-like at 25°C
Vegetative Growth

13. budding yeast.
Parent cell
Bud
Bud scar

14. Fungal dimorphism.
Yeastlike growth Moldlike growth

15. YEASTS
• Yeasts are capable of facultative anaerobic growth.
Yeasts can use oxygen or an organic compound as the final
electron acceptor
- If given access to oxygen, yeasts perform aerobic respiration to
metabolize carbohydrates to carbon dioxide and water;
- denied oxygen, they ferment carbohydrates and produce
ethanol and carbon dioxide. This fermentation is used in the
brewing, wine-making, and baking industries.
Saccharomyces species produce ethanol in brewed beverages
and carbon dioxide for leavening bread dough.

16. Fungi versus bacteria
Environmental requirements and nutritional characteristics
• Fungi usually grow better in an environment with a ≤ pH 5, which is
too acidic for the growth of most common bacteria .
• Almost all molds are aerobic. Most yeasts are facultative anaerobes.
• Most fungi are more resistant to osmotic pressure than bacteria;
most can therefore grow in relatively high sugar or salt concentrations.
• Fungi can grow on substances with a very low moisture content,
generally too low to support the growth of bacteria.
• Fungi require somewhat less nitrogen for growth than bacteria.
• Fungi are often capable of metabolizing complex carbohydrates,
such as lignin (a component of wood), that most bacteria cannot use for
nutrients.

17. Life Cycle
• Filamentous fungi can reproduce asexually by fragmentation
of their hyphae.
• Both sexual and asexual reproduction in fungi occurs by the
formation of spores
- Unlike the bacterial endospore, this is a true reproductive
spore: a second organism grows from the spore.
• Fungal spores can be either asexual or sexual. -
Asexual spores are formed by the hyphae of one organism. When
these spores germinate, they become organisms that are
genetically identical to the parent.
- Sexual spores result from the fusion of nuclei from two opposite
mating strains of the same species of fungus.
• Fungi are usually identified by spore type.

18. Asexual spores
Conidiophore
- Philaide, spore that is not
enclosed in a sac. -
Conidia are produced in a
chain at the end of a
conidiophore.
Such spores are produced
by Aspergillus
FIGURE 45-6 A. fumigatus. Phialides form on top of a
swollen vesicle at the end of a long conidiophore. The basal
conidia are the youngest. Mature conidia have rough walls.

19. Arthrospores
Arthrospores
Conidia formed by the
fragmentation of a
septate hypha into
single, slightly thickened
cells are
called arthroconidia.
Coccidioides immitis produces
such spores

20. Pseudohypha
Blastoconidia
Blastoconidia
consists of buds coming
off the parent cell.
Such spores are found in some
yeasts, such as Candida albicalls
and Cryptococcus

21. Chlamydoconidium
Chamydoconidium -
a thick-walled spore
formed by rounding and
enlargement
within a hyphal segment
Chlamydoconidia are produced by
the yeast C. albicalls.

22. Sporangiospores
Sporangiophore
• Sporangiospore -- asexual spore
formed within a sporangium (sac)
, at the end of an aerial hyphae
called a sporangiophore.
The sporangium can contain
hundreds of sporangiospores
Such spores are produced by
Rhizopus.

23. Sexual Reproduction
Three phases:
– Plasmogamy: haploid donor
cell nucleus (+) penetrates cytoplasm of
recipient cell (−)
– Karyogamy: + and − nuclei fuse
– Meiosis: diploid nucleus produces
haploid nuclei
(sexual spores)
Sexual Spores
 Zygospore: fusion of haploid cells produces one zygospore
 Ascospore: formed in a sac (ascus)
 Basidiospore: formed externally on a pedestal (basidium)

24. Medically Important Phyla of Fungi
• Glomerulomycota (previously
Zygomycota)
Order - Mucorales
• Ascomycota
• Basidiomycota

25. The life cycle of Rhizopus, a zygomycete.
Sporangiospore
Spore germinates
to produce hyphae.
Vegetative mycelium grows.
Sporangium
Sporangiophore
Sporangium
bursts to release
spores.
Aerial hypha
produces a
sporangium.
Gametes form
at tip of hypha.
Sporangiospores
Spore germinates
to produce hyphae.
Spores are released
from sporangium.
Zygote produces
a sporangium.
Karyogamy
and meiosis.
Zygosporangium
containing zygospore
Zygospore
forms.
Plasmogamy.
Sexual
reproduction
Asexual
reproduction
1
2 3
4
5
6
7
8
9
10
11

26. Ascomycota
• Sac fungi
• Septate
– Produce sexual and asexual spores
• Ascospores and frequently conidiospores
– Aspergillus (opportunistic, systemic mycosis)
– Blastomyces dermatitidis, Histoplasma
capsulatum (systemic mycoses)
– Microsporum, Trichophyton (cutaneous mycoses)

27. FThe life cycle of Talaromyces, an ascomycete.
Vegetative mycelium grows.
Sexual
reproduction
Asexual
reproduction
Conidium germinates
to produce hyphae.
Ascospore germinates
to produce hyphae.
Conidia are
released from
conidiophore.
Hypha produces
conidiophore.
Conidia
Conidiophore
Ascus opens to
release ascospores.
Meiosis
then mitosis.
Karyogamy.
Plasmogamy.
Ascospore
– +
1
2
3
4
5
6
7
8
9

28. Basidiomycota
• Club fungi
• Septate
• Produce basidiospores and sometimes
conidiospores
– Cryptococcus neoformans (systemic mycosis)

29. Economic Effects of Fungi
• Saccharomyces cerevisiae: bread, wine, HBV
vaccine
• Trichoderma: cellulase
• Taxomyces: taxol (anticancer chemotherapy)
• Entomophaga: biocontrol
• Coniothyrium minitans: kills fungi ( antifungal)
• Paecilomyces: kills termites

30. Fungal Diseases (Mycoses)
• Systemic mycoses: deep within body
• Subcutaneous mycoses: beneath the skin
• Cutaneous mycoses: affect hair, skin, and nails
• Superficial mycoses: localized, e.g., hair shafts
• Opportunistic mycoses: caused by normal
microbiota or environmental fungi

31. Fungal diseases( Mycoses)
• Out of 400 species of pathogenic fungi less than 50
are responsible for more than 90% of the fungal
infections of humans and other animals
• Overall, most mycoses are caused by
- noninvasive molds that have adapted to grow on
the skin, hair, or nails, and
- endogenous species of Candida, which are
members of the human microbiome.
• Pathogenic fungi are not contagious (with the
exception of dermatophytes)
- transmission among humans or animals is
extremely rare

32. Diagnosis of fungal diseases
• There are five approaches to the laboratory
diagnosis of fungal diseases:
(1) direct microscopic examination
(2) culture of the organism,
(3) PCR
(4) DNA probe tests,
(5) serologic tests.
• Direct microscopic examination of clinical specimens
(sputum, lung biopsy material, skin scrapings etc)
aims to find characteristic asexual spores, hyphae,
or yeasts in the light microscope after treatment
with KOH and staining with special fungal stains
Calcofluor white
staining

33. Antifungal chemotherapy

34. Jawetz Chapter 45 pp.673-681
Tortora Chapter 12 Fungi