Fungal Diversity

1
Fungal Diversity

• Reading Chap. 31
• I. Introduction
• A. What is a fungus?
• B. What does a fungus do?
• C. Basic fungal life cycle
• D. Who cares about fungi?
• II. Fungal Phyla
• A. Overview
• B-E. Life cycles of the phyla
• III. Fungal mutualisms
• A. Lichens
• B. Mycorrhizae

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Characteristics of Fungi

• Non-motile eukaryotes lacking chlorophyll
• Contain nucleus, mitochondria, 80S ribosomes
• Plasma membrane contains ergosterol instead of
  cholesterol.
• Cell wall is composed of chitin and various
  glucans, mannans, and complex polysaccharides
• Larger than bacteria
• Relatively simple nutritional requirements, wide
  range of growth rates
• Form visible colonies in days to weeks
• Unicellular or multicellular depending on the
  species

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Molds

• Multicellular, tubular structures (hyphae)
• Hyphae can be septate (regular crosswalls) or
  nonseptate (coenocytic) depending on the species
  (grow by apical extension)
• Vegetative hyphae grow on or in media (absorb
  nutrients) form seen in tissue, few
  distinguishing features
• Aerial hyphae contain structures for production
  of spores (asexual propagules) usually only seen
  in culture

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Fungi

• The parts

Fig. 31.1
Cell walls - made of chitin. Same material that
is in the external skeletons of arthropods -
insects, arachnids, and crustaceans.
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Molds - identification

• Identification based on colony morphology
  (pigment, texture) and morphology of reproductive
  structures
• Conidia - spores formed by budding
  (blastoconidia) or disarticulation of existing
  hypha (arthroconidia)
• Sporangiospores - produced by free-cell formation
  within sporangium in nonseptate molds

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1

• sporangium
• sporangiophore
• Endospores
• Nonseptate
• hyphae
• 5. rhizoids

• Conidiopspores
• Phialides
• Vesicle
• Conidiophore
• Septate hyphae

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2
3
4
2
5
4
5
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YEASTS

• Also yeasts - single-celled
• e.g., Saccharomyces cerevisiae
• Candida albicans

31.15
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Yeasts

• Unicellular, 3-5 µm, reproduce by budding
  (blastoconidia formation) or fission
• Identified by microscopic morphology (grow on
  cornmeal agar) and biochemical tests (sugar
  assimilation, enzymatic activity).
• Molds and yeast are not exclusive forms, some
  species may exist in both yeast and mold forms
  (dimorphism).

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Colonial Morphology of Fungi
Cryptococcus neoformans
Wangiella dermatitidis
Trichophyton tonsurans
Candida albicans
Aspergillus fumigatus
T. menta-grophytes
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FUNGAL LIFE CYCLE Asexual - budding or cell
division Sexual - fusion of 2 mating
types spore formation
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FUNGAL NUTRITION ENVIRONMENT Organic
compounds needed for growth saprophytes as feed
on dead organic matter Adapted to growth at
pH 5 growth on surfaces growth under high
osmotic conditions growth at low water
levels growth in low nitrogen environments
growth on unusual nutrient sources
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B. What does a fungus do?

• Absorptive heterotroph
• Such as

Detritivore
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Also eat - wood in houses, boats, fences -
food - other materials - cloth, paint, leather,
waxes, jet fuel, petroleum, paper, wire
insulation, photographic film, - to name a few.
What do all of these materials have in common?
They are all C-based.
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C. Basic fungal life cycle
2. Fertilization doesnt happen all at once
Plasmogamy - fusion of cytoplasm Karyogamy -
fusion of nuclei (gametes) heterokaryotic dikaryo
tic
fig. 31.2
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Classification of Fungi

• Taxonomy is based on structural features of the
  teleomorph (sexual phase).
• Zygomycota - includes all fungi with nonseptate
  hyphae
• Ascomycota - includes most human pathogens
• Basidiomycota - mainly saprobes or plant
  pathogens
• Deuteromycota (fungi imperfecti)
• Sexual phase unknown or doesnt exist. Some can
  be assigned to above groups based on phylogenetic
  analysis.

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B. Zygomycota

• 1. No dikaryotic growth
• 2. Both sexual and asexual sporangia

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C. Ascomycota - Life cycle
1. Dikaryotic growth 2. Fruiting body
ascocarp 3. Fertile layer with asci 4. Eight
ascospores per ascus (sac) 5. Asexual
reproduction via conidia
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D. Basidiomycota - Life cycle
1. Dikaryotic growth 2. Fruiting body
basidiocarp 3. Fertile layer on gills with
basidia (clubs) 4. Four spores per
basidium 5. Asexual reproduction is rare
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E. Deuteromycota - fungi imperfecti

• 1. Not a true phylum (not a natural group)
  polyphyletic
• 2. Fungi with no known sexual reproduction
• 3. Asexual reproduction by conidia

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III. Fungal mutualisms
Definitions Symbiosis - 2 organisms living
together in intimate physical contact Mutualism
- both organisms benefit from the
relationship Parasitism - one benefits, one
loses Commensalism - one benefits, other not
affected
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A. Lichens
1. Partners a. Fungal partner - gives
protection - mostly Ascomycetes (25,000
spp.) - only found in lichens (not
free-living) b. Photosynthetic partner -
gives fixed carbon (sugars) - green alga or
cyanobacterium - can be free-living
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A. Lichens
a. most of lichen body is fungal hyphae b.
photosynthetic partner in a distinct layer c.
sexual reproduction of fungal partner only d.
asexual reproduction soredia, fragmentation
2. Anatomy
medulla
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Figure 29.9a
Ectomycorrhizal fungi (EMF)
Root cells
EMF
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A. Lichens
3. Morphology
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A. Lichens

• 4. Importance
• a. rock weathering, soil formation in primary
  succession
• - acid secretion
• - trapping particulates
• nitrogen fixation (cyanobacteria)
• b. Indicators susceptible to pollutants