Environmental Engineering Reference
In-Depth Information
Figure 6.1
Fungal colonies.
A. Reproduction
Specialized reproductive structures develop in the life history of all fungal
species. These structures may be produced as a consequence of sexual or
asexual processes. Most species of fungi undergo both sexual and asexual
reproduction at some time in their life history. Sexual processes occur in
specialized cells or structures, with the production of spores that will ulti-
mately be dispersed. Sexual spores are produced in specialized “fruiting”
structures. The most noticeable of these are mushrooms and bracket fungi
on trees or tree debris.
Asexual spores, as well as the fruiting structures (if any) on or within
which they are borne, vary in size and shape as well. Asexual spores are
produced in large masses, particularly when a mold colony is maturing and
experiencing environmental stress, e.g., depletion of substrate, lower substrate
moisture content or air relative humidity, or competition with other colonies
or species. In many cases, asexual spores produce pigments which may, along
with pigment in the mycelium, characterize colonies in culture or on natural
substrates. Both spore-forming structures and asexual spores for species in
the genera
can be seen in
Figures 6.2
and
6.3
.
Fungi may also produce spores or other structures that are designed to
survive harsh environmental conditions. These include thick-walled, dor-
mant clamydospores and hardened mycelial masses called sclerotia.
A number of species of fungi grow as single cells during all or part of
their life history. Most notable of these are yeasts, which reproduce asexually
by budding and sexually by producing sac-like ascospores. In genera such
as
Penicillium
and
Aspergillus
, under certain environmental conditions the organism develops
yeast-like growth, while under others, it develops a typical mycelium.
Candida
B.
Dispersal
Most fungal species produce sexual and/or asexual spores which serve to
both reproduce the organism and disperse it to new substrates. As a conse-
