Introduction to Lab 4: Ex. Fungi - Molds

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Introduction to Lab 4 Ex. Fungi - Molds The
purpose of this exercise is to study some
representative genera of molds. This exercise
will be entirely covered with the use of demos.
The reason for this being molds can be
hazardous organisms to study in the lab.
Molds are identified based on physical
structures that they produce when grown on the
surface of artificial culture media.
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Structure Molds are filamentous structures
(hyphae) that intertwine to form a mass called
the mycelium. The hyphae that are responsible
for the absorption of nutrients from the
environment are called the vegetative hyphae and
are found close to or embedded in the culture
medium. When the mold starts producing spores
for reproduction (especially asexual) these
spores are borne above the surface to
facilitate their dispersal into the environment.
The hyphae that produce the asexual spore
structures are hence called aerial hyphae.
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Since the spore structure is ideally suited for
its purpose of easy dispersal, they are very
light and can be dislodged very easily from the
aerial hyphae. Hence extra precautions have to
be used when handling mold cultures. They can be
opened only under a containment hood with
appropriate personal protection to avoid
exposure to these spores. Hyphae may be
coenocytic or septate. When present septa may
be of one of three kinds. Asexual structures are
the spores found within a sac or without a sac
but associated with other structures. Sexual
spores are the features used in classification of
Fungi. They may be of different kinds.
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Specimens on demo these include stained slides
and cultures of mold growth for observation.
Mold slides are prepared by tease mount or
slide culture preparations. Appropriate stains
are used to color the filaments and other
structures. Cultures of molds are grown using
culture media that are suited for their growth,
i.e., acidic pH media. Genera Zygomycotina
Rhizopus sp., Phycomyces sp. Ascomycotina
Aspergillus sp., Penicillium sp.
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Rhizopus - coenocytic hypha, (specific
characteristic rhizoids and columella in
sporangia) asexual structures - sporangia and
spores, sexual spore zygospore.
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Phycomyces slide showing zygospore formation
culture plate with the two opposing strains and
zygospores formed at the meeting of the hyphae
of opposing strains.
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Ascomycotina - Aspergillus niger, A. ochraceus
septate hypha, conidia with vesicle and
sterigmata specific afro head appearance to
conidial head. Plate black pigmented, powdery
growth
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Penicillium septate hypha, conidia with
sterigmata specific branched conidiophores
paint brush-like appearance to the conidial
structures. Plate greenish and white growth,
powdery appearance