The Problem: Mold
There are thousands of known species of molds, which
include opportunistic pathogens, saprotrophs, aquatic species and thermophiles.
Like all fungi, molds derive energy not through photosynthesis but from
the organic matter on which they live. Typically, molds secrete hydrolytic
enzymes, mainly from the hyphal tips. These enzymes degrade complex biopolymers
such as starch, cellulose and lignin into simpler substances which can
be absorbed by the hyphae. In this way, molds play a major role in causing
decomposition of organic material, enabling the recycling of nutrients
throughout ecosystems. Many molds also secrete mycotoxins which, together
with hydrolytic enzymes, inhibit the growth of competing microorganisms.
Molds reproduce through small spores, which may contain a single nucleus
or be multinucleate. Mold spores can be asexual (the products of mitosis)
or sexual (the products of meiosis); many species can produce both types.
Some can remain airborne indefinitely, and many are able to survive extremes
of temperature and pressure.
Although molds grow on dead organic matter everywhere in nature, their presence
is only visible to the unaided eye when mold colonies grow. A mold colony
does not comprise discrete organisms, but an interconnected network of
hyphae called a mycelium. Nutrients and in some cases organelles may be
transported throughout the mycelium. In artificial environments like buildings,
humidity and temperature are often stable enough to foster the growth of
mold colonies, commonly seen as a downy or furry coating growing on food
or other surfaces.
Some molds can begin growing at temperatures as low as 2°C. When conditions do
not enable growth, molds may remain alive in a dormant state, within a large
range of temperatures before they die. The many different mold species vary enormously
in their tolerance to temperature and humidity extremes. Certain molds can survive
harsh conditions such as the snow-covered soils of Antarctica, refrigeration,
highly acidic solvents, and even petroleum products such as jet fuel.
Xerophilic molds use the humidity in the air as their only water source; other
molds need more moisture.