Introduction to the Fungi and Fungal Ecology

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Introduction to the Fungi andFungal Ecology
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Fungi are eukaryotic organisms that are neither
plant nor animal
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Fungi include molds
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Mushrooms
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Puffballs
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Bracket Fungi
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Fungi can be unicellular such as yeast
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Fungi usually have a thread like body made up of
hyphae
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Hyphae make up the mycelium
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Hyphae also make up the structure of fruiting
bodies such as mushrooms
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Fungal Cell Wall

• 90 polysaccharide
• Also contains proteins and some lipids
• Fibrils embedded in a matrix
• Major fibrillar component is chitin
• Some groups have cellulose

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Chitin --straight chain polymer of N-acetyl
glucosamine--glucosamine units joined by
?-1,4-bonds
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Matrix

• Various polysaccharides and proteins
• Matrix polysaccharides often more abundant than
  chitin
• Most thoroughly studied are the ?-glucans
• ?-glucans often used in assays of fungal growth
  or contamination

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Fungi reproduce by spores
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Spores can result from sexualor asexual
reproduction
Mycelium
Sexual Spores
Asexual Spores
Mycelium
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Life Cycle Stages

• Sexual Stage Perfect Stage Teleomorphic Stage
• Asexual Stage Imperfect Stage Anamorphic Stage

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Types of Asexual Spores
Sporangium
Conidia on hyphae
Sporangiospore or just spore
Conidium
Conidiophore
Sporangiophore
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Rhizopus Sporangium
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Chains of Conidia
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Sexual spores

• Result from genetic recombination
• Follow karyogamy
• In most fungi meiosis is zygotic
• Sexual spores often form in a specialized
  fruiting body
• Basis for classification

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Sexual Reproduction and Life Cycles

• Sexual reproduction is fusion of gametes
• Gamete (n) gamete (n) ---gt zygote (2n)
• Plasmogamy and karyogamy
• In many fungi, karyogamy is delayed and a
  DIKARYON (n n) is formed

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Simple Life Cycle with predominantly haploid life
cycle. Zygote is the only diploid cell - no
dikaryon
Mycelium
Asexual Spore
Karyogamy
Zygote
Mycelium
Meiosis
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Life Cycle with predominantly haploid life cycle.
Zygote is the only diploid cell - short dikaryon
phase
Mycelium
Asexual Spore
Plasmogamy
Mycelium
Meiosis
Karyogamy
Zygote
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Life Cycle with predominantly dikaryon life
cycle. Zygote is the only diploid cell - short
haploid phase
Plasmogamy
Mycelium
Asexual Spores
Haploid spore
Meiosis
Zygote
Karyogamy
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Fungal Classification

• 75,000 known species
• Estimates of 1.5 million total
• Classification based on method of sexual
  reproduction
• Generally agreed that fungi are polyphyletic and
  reflect several distinct evolutionary lines
• Fungi classified in two or three kingdoms
  Protista, Chromista, and Fungi

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Kingdom Eumycota
Div Chytridiomycota Div
Zygomycota Div
Ascomycota Div
Basidiomycota
Asexual Fungi
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Classification of the Fungi for Environmental
Microbiology

• KINGDOM PROTISTA Eukaryotic organisms with
  heterotrophic or autotrophic nutrition
  (protozoans, algae, and fungal-like organisms)
• DIVISION MYXOMYCOTA - true slime molds
  plasmodial feeding stage spores formed in a
  fruiting body
• DIVISION OOMYCOTA - mycelial fungi with
  non-septate hyphae most form zoospores sexual
  spores (oospores) are thick-walled resting spores
• KINGDOM FUNGI True Fungi (mycelial or yeast)
  with an absorptive, heterotrophic nutrition
• DIVISION CHYTRIDIOMYCOTA - primitive fungi,
  flagellated asexual spores
• DIVISION ZYGOMYCOTA - mycelial fungi with
  non-septate hyphae sexual spores (zygospores)
  are thick-walled resting spores asexual spores
  (sporangiospores) produced in a sporangium
• DIVISION ASCOMYCOTA - mycelial fungi or yeasts
  sexual spores (asocospores) formed in an ascus
  asexual spores (conidia) abundant in some
• DIVISION BASIDIOMYCOTA - mycelial fungi or
  yeasts sexual spores (basidiospores) formed on a
  basidium asexual spores abundant in two classes
• ASEXUAL FUNGI - mycelial fungi no sexual stage
  asexual spores are conidia most are anamorphs of
  the Ascomycota

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Polyphyletic Origin

• Evidence comes from
• Cell wall composition chitin vs cellulose
• Cellular metabolism
• pathway for lysine synthesis (alpha aminoadipic
  acid pathway vs diaminopimelic acid pathway)
• sterols
• storage compounds
• Molecular systematics DNA evidence
• Ultrastructure

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Although fungal-like organisms are now
classified in two or more kingdoms, the term
fungus is still used in the traditional sense to
refer to any and all organisms studied by
mycologists.

• David Hawksworth, 1991

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Myxomycota Vegetative Phase of a Slime Mold
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Myxomycota Reproductive Phase of a Slime Mold -
Stemonitis Sporangia
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Slime Molds
Perichaena depressa
Physarum roseum
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Many members of the Oomycota are true water molds
with motile spores
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Other members of the Oomycota are plant pathogens
with airborne spores
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Members of the Zygomycota produce asexual spores
in a sporangium
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The zygospore (zygosporangium) is the
characteristic sexual structure of the Zygomycota
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Characteristic sexual structure of the Ascomycota
is the ascus containing 8 ascospores
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Single ascus with 8 ascospores produced by a yeast
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Ascomycota

• Many members of the Ascomycota develop asci
  within a fruiting body.
• Fruiting bodies often called ascocarps or ascoma
• Ascocarps can be
• Cleistothecia
• Perithecia
• Apothecia
• Other

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Flask-shaped fruiting body known as a perithecium
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Cup-shaped fruiting body (apothecium)
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Morels are also apothecia
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Asci with ascospores from a morel
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Basidiomycota

• The most conspicuous fungi in the environment
• Basidiospores are typically produced in a large
  fruiting body (basidiocarp or basidioma)
• Fruiting bodies include
• Mushrooms
• Bracket Fungi
• Puffballs

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Ganoderma Common Wood Rotter
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Calvatia Common Puffball
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Four Basidiospores are Produced Externally on
Basidia
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Basidia Line the Pores of Bracket Fungi
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And the Gills of Mushrooms
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Single Basidium with 4 Basidiospores
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Rusts and Smuts

• Basidiomycota also includes two groups of fungi
  that lack basidiocarps
• Rust fungi and smut fungi
• Important pathogens on both native and cultivated
  plants

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Stem Rust of Wheat
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One Spore Stage in Wheat Rust
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Life Cycle of Stem Rust of Wheat Has 5 Spore
Stages
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Loose Smut of Wheat
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Asexual Fungi

• Constitute an artificial group based only on
  asexual spores (morphology and development)
• Most are members of the Ascomycota with a small
  percent members of the Basidiomycota
• Also called
• Mitosporic Fungi
• Deuteromycetes
• Imperfect Fungi (Fungi Imperfecti)
• Anamorphic Fungi
• Artificial classification into families and orders

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Asexual Fungi Cladosporium
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Alternaria
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Curvularia
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Penicillium Conidiophore
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Penicillium Culture
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Aspergillus Conidiophore
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Fungal Physiology

• Fungi are true heterotrophs with an absorptive
  nutrition
• Depend on external sources of organic material
  for both energy and building blocks
• Produce extracellular enzymes that digest complex
  organic molecules that are then absorbed
• Produce a variety of secondary compounds

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Life styles of absorptive heterotrophs

• Parasites
• Mutualistic symbionts
• Saprobes

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Fungal Ecology

• Fungi are ubiquitous in the environment
• Almost any organic substrate can be colonized
• Some generalities
• Moisture requirement less than other organisms -
  fungi can grow in dust
• Generally aerobic
• Wide range of tolerance to pH, temperature,
  oxygen, light, salinity, etc

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Temperature Ranges for Select Fungi
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Substrate Characteristics of Decomposer Fungi

• Classical fungal succession theory
• Saprophytic sugar fungi - depend on simple
  organic compounds
• Cellulolytic fungi - able to degrade common
  polymers
• Lignin degrading fungi - able to degrade the most
  complex polymers
• Secondary sugar fungi - co-exist with polymer and
  gain sugars from their activities

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Behavioral Groupings of Decomposer Fungi

• Combines substrate, environmental interactions
  and interactions with other organism
• Pathogens and weak parasites
• Pioneer saprotrophic fungi
• Polymer degrading fungi
• Degraders of recalcitrant compounds
• Secondary opportunitists

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Fungal Identification

• Sampling
• Direct microscopy
• Culturing
• Biolog microtiter plate assays
• Ergosterol assays
• Beta-glucan assays
• Immunochemistry
• Molecular biology