Characteristics of Yeasts

1
Characteristics of Yeasts

• Yeast grow as smooth moist colonies with a
  buttery consistency
• Some yeast colonies are mucoid due to a large
  polysaccharide (gelatinous or mucoid) capsule

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Butyrous Glabrous Growth of Yeast
3
Characteristics of Yeasts

• Yeast typically cannot be identified by
  morphologic features alone because they lack
  variety in their appearance
• The identity of yeast is determined by a
  combination of morphologic and biochemical
  criteria

4
Characteristics of Molds

• Moulds (molds) are filamentous multicelled fungi
  that reproduce sexually and/or asexually in a
  variety of ways
• Long thin tube-like structures (germ tubes)
  emanate from sexual or asexual propagules to
  form septate or non-septate hyphae
• Hyphae tend to form branches
• Intertwining hyphae form matted growth know as
  the mycelium

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Initiation of Hyphal Growth
Propagule
Germ tube
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Characteristics of Molds

• Crosswalls may develop and divide the elongated
  germ tube (now called a hyphae) into sections.
  This is known as septate hyphae
• In one group of fungi (the zygomycetes)
  crosswalls are absent or rare (non-septate or
  aseptate)

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Septate Fungal Hyphae
Septa
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Nonseptate (or sparsely septate) Hyphae
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Characteristics of Molds

• Hyphae that grow on top of the substrate and
  protrude into the air intertwine to form aerial
  mycelium (vs vegetative mycelia)

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Characteristics of Molds

• Asexual propagules that develop laterally or
  terminally from hyphae (conidiophores) are
  conidia (pleural) or conidium (singular). The
  cells in the hyphae from which they form are
  termed conidiogenous cells.
• 2 forms of conidial development
• 1.Blastic enlargement or "blowing out" of a
  conidial initial before being delimited by a
  septum.
• 2.Thallic septum formed prior to conidial
  enlargement