Fungal Growth and Sporulation

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Fungal Growth and Sporulation
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G. T. Cole. 1986. Microbiol. Rev. 50 95-132
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From Fischer-Parton et al. 2000. J. Microscopy
198 (3) 246-259
Exocytosisenzymes (pectinases, cellulases,
proteases) to degrade compounds in the
environment Endocytosisremoval of excess plasma
membrane, recycling membrane proteins, transport
of membrane proteins lipids to vacuole for
degradation, uptake of molecules, etc.
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Components of wall synthesis at hyphal tip.
Modified from Deacon (2006). Fungal
Biology.
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Asexual Sporulation

• Sporangiospores formed by cleavage of protoplasm
  in a multinucleate sporangium (Chytridiomycota,
  Zygomycota, Oomycota)
• Conidia develop directly from hyphae or from
  modified hyphal cells called conidiogenous cells
  (Ascomycota including Deuteromycetes, some
  Basidiomycota)

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Control of asexual sporulation

• May be triggered by changes in carbonnitrogen
  ratio in growth medium
• May require light trigger, e.g. near-ultraviolet
  light
• Under control of sporulation genes
• One group involved in switch from somatic growth
  to sporulation
• A second group regulates developmental stages of
  sporulation
• A third group regulates secondary aspects
  including spore color

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Asexual Fungi Deuteromycetes
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Deuteromycetesdeuter- Gk., meaning second

• gt 20,000 species of fungi in 2600 genera have no
  known sexual state
• Most belong in phylum Ascomycota
• These fungi are also called
• Anamorphic fungi
• Mitosporic fungi
• Conidial fungi
• Imperfect fungi
• Fungi imperfecti

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Asexual propagules

• Chlamydospore
• 1-celled spore (usually thick-walled) designed
  for perennation formed inside existing cell
• Sclerotium (pl. sclerotia)
• Rounded mass of hyphae, often differentiated into
  rind and medulla

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Asexual propagules

• Conidium (pl. conidia)
• Non-motile spore designed for dispersal
• Wide range of shape, size, color and septation
  among taxa

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Saccardoan Spore Types

• P.A. Saccardo (1845-1920)
• Sylloge Fungorum (1882-1972)--names
  descriptions of all known fungi
• Developed system of classifying fungi based on
  type of spore (shape, septation, color)

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Saccardoan Spore Types

• Color
• Hyaline or bright (hyalo-)
• Pigmented (phaeo-)
• Shape and septation
• 1-celledamerospore
• 2-celleddidymospore
• Multicelledphragmospore
• Muriformdictyospore
• Filiformscolecospore
• Helicalhelicospore
• Branched--staurospore

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Saccardoan Spore Types
scolecospore
amerospore
staurospore
helicospore
dictyospore
phragmospore
didymospore
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Synanamorph

• Two or more types of asexual spores formed by the
  same fungus
• Example
• Ceratocystis fibriata

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Conidiogenous Cells

• A cell that forms one or more conidia
• May be formed on a specialized simple or branched
  hypha called a conidiophore

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From D. Malloch
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Conidial Development (Ontogeny)

• Blasticblowing out of conidial initial prior to
  formation of delimiting septum
• Thallicconversion of segment of existing hyphae
  into conidia

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Blastic versus thallic
Cole, 1986
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Blastic development

• Holoblastic
• single conidium is formed from conidiogenous
  locus, all wall layers involved in formation of
  conidium wall
• Enteroblastic
• more than one conidium formed from locus, only
  the inner wall layer(s) involved in formation of
  conidium wall

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Holoblastic
From Hawksworth et al., 1995
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Holoblastic/synchronous
Holoblastic/sympodial
From Hawksworth et al., 1995
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Enteroblastic development

• Phialidica basipetal succession of conidia is
  formed from a fixed locus on the conidiogenous
  cell (phialide)

collarette
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Enteroblastic development

• Annellidica basipetal succession of conidia
  formed by repeated percurrent proliferation of
  conidiogenous locus, leaving the distal end of
  locus with transverse scars (annellations)

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Enteroblastic development

• Treticthe inner wall of the conidiogenous cell
  blows out through a hole (pore) in the outer wall
  like a balloon to form a conidium.

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Arrangement of conidia at locus

• Solitary 
• Catenate true chains
• Seriate false chains, spore heads
• Dry spores
• Wet spores (gleoid)

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Succession of conidia

• Basipetal a chain of conidia in which new
  spores are formed at the base, the oldest conidia
  are at the apex
• Acropetal a chain of conidia with the new
  spores formed at the end of the chain, oldest
  spores are at the base. In order for this type
  of conidial formation to occur, the conidia must
  function as conidiogenous cells (e.g.,
  Alternaria, Cladosporium)

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Alternaria
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Alternaria
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Cladosporium
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Conidiophores

• Hyphae bearing conidiogenous cells
• Morphologically differentiated from vegetative
  hyphae (macronematous)
• Morphologically not differentiated
  (micronematous)

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Conidiophores
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Types of Deuteromycetes

• Hyphomycetesfungi that produce conidia from
  conidiogenous cells free on their mycelia
• May be formed on the surface of synnemata or
  sporodochia
• Coelomycetesfungi that produce conidia from
  conidiogenous cells formed in conidiomata

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Synnemata

• Conidiophores united at base
• Conidiogenous cells at apex

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Sporodochium

• A compact, cushion-like aggregation of hyphae on
  which conidiophores are formed in a dense layer
• The aggregation of hyphae is called a stroma (pl.
  stromata)

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Hyphomycetes

• Moniliaceaeconidiophores formed singly, hyphae
  and conidia pale-colored
• Dematiaceaeconidiophores formed singly, hyphae
  and/or conidia dark-colored
• Tuberculariaceaeconidiophores aggregated on
  cushion-like sporodochium (pl. sporodochia)
• Stilbaceaeconidiophores aggregated in a synnema
  (pl. synnemata), an erect bundle with conidia
  formed at apex