Environmental Engineering Reference
In-Depth Information
from
). Many of the fungal allergens identified by
medical scientists have been associated with species of Ascomycota.
The division Basidiomycota, historically known as basidiomycetes,
includes a large variety of fungal types and species. They are characterized
by their sexual reproduction processes, which produce basidiospores on
structures called basidia. Basidiospores are the primary means of dispersal,
though asexual spores may also be formed. Basidiomycetes include yeasts
like
Penicillium
and
Aspergillus
which colonize indoor substrates; rusts and smuts, which
are plant pathogens; many species of mushrooms, bracket fungi, and puff-
balls; and a variety of other wood-decaying fungi which grow on structural
timbers in human dwellings. The basidiomycetes rarely form fruiting bodies
in culture (sexual or asexual) and, as a consequence, are difficult to identify.
In addition, many do not grow well in culture.
The Deuteromycetes, also known as fungi imperfecti or asexual fungi,
include a group of organisms classified by their asexual reproductive struc-
tures and apparent absence of sexual structures. This is an artificial classifi-
cation, since the sexual stage is not commonly observed under culture con-
ditions. Many deuteromycetes have been determined to be ascomycetes,
while only a few are basidiomycetes. Classifications in this group have been
problematic, since the asexual stage of Deuteromycete genera such as
Sporobolomyces,
Aspergillus
may be associated with different genera in the Ascomycota. Topics
used to identify species such as
typically use the
Deuteromycete name rather than the more scientifically correct name, which
is based on the sexual stage.
Aspergillus
and
Penicillium
II. Biologically significant fungal compounds
As fungi grow, they produce a variety of secondary metabolites. These are
often species-dependent, but a number of compounds appear to be generic
to fungi. These include pigments which may color spores or other structures
or diffuse into substrates, a variety of volatile organic compounds (MVOCs)
with their distinctive musty or earthy odors, alkaloids, antibiotics, and myc-
otoxins. Many secondary metabolites are produced by older parts of fungal
colonies, particularly cells that are being restricted in their growth.
Some metabolites may have important direct functions. It is notable that
genera found outdoors, such as
Cladosporium, Epicoccum, Alternaria,
and
Pith-
omyces,
are dark in color, producing black spores. Many mushrooms produce
dark spores as well. The major benefit of dark spores and mycelium would
be to protect the organism from ultraviolet light. Other metabolites may serve
to reduce competition with different organisms (antibiotics and bacteria),
other species, or members of the same species (alkaloids, mycotoxins).
A. MVOCs
During their growth, all fungal colonies release volatile organic compounds
(VOCs or, more specifically, MVOCs to denote their microbial origin) that
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