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CULTURING MUSHROOM MYCELIUM ON AGAR MEDIA 101
become infected. (See Figure 81.) Mycelium
arising from such germinations are frequently
associated with a high contamination rate, unfortunately
often not experienced until the
mycelium is transferred to grain media. However,
if the spore prints are made correctly,
contamination is usually not a problem.
Once inoculated, the petri dish cultures
should be taped with an elastic film (such as
ParafilmTM) which protects the incubating
mycelium from intrusive airborne contaminants.
(See Figure 58.)
Purifying a Culture
Many cultures originating from spores or tissue
are associated with other micro-organisms.
Several techniques are at one's disposal for
cleaning up a culture. Depending upon the type
and level of contamination, different measures
are appropriate.
One way of cleaning a bacterially infested
culture is by sandwiching it between two layers
of media containing an antibiotic such as
gentamycin sulfate. The hyphae, the cells composing
the mycelium, are arranged as long
filaments.These filamentous cells push through
the media while the bacteria are left behind. The
mycelium arising on the top layer of media will
carry a greatly reduced population of bacteria,
if any at all. Should the culture not be purified
the first time using this procedure, a second
treatment is recommended, again subculturing
from the newly emerged mycelium. Repeated
attempts increase the chances of success.
If the culture is mixed with other molds, then
the pH of the media can be adjusted to favor the
mushroom mycelium. Generally speaking,
many of the contaminant fungi are strong
acidophiles whereas Oyster mushrooms grow
well in environments near to a neutral pH. If
these mold fungi sporulate adjacent to the
mycelia of mushrooms, isolation becomes difficult.
* Remember, the advantage that molds
have over mushroom mycelia is that their life
cycles spin far faster, and thousands of mold
spores are generated in only a few days. Once
molds produce spores, any disturbance—including
exposure to the clean air coming from
the laminarfiow hood—creates satellite colonies.
One rule is to immediately subculture all
points of visible growth away from one another as
soon as they become visible. This method disperses
the colonies, good and bad, so they can be
dealt with individually. Repeated subculturing
and dispersal usually results in success. If not,
then other alternative methods can be implemented.
Mycelia of all fungi grow at different rates
and are acclimated to degrading different base
materials. One method I have devised for separating
mushroom mycelium from mold
mycelium is by racing the mycelia through organic
barriers. Glass tubes can filled with finely
chopped, moistened straw, wood sawdust, even
crushed corncobs (without kernels) and sterilized.
The contaminated culture is introduced to
one end of the tube. The polyculture of contaminants
of mushroom mycelium races through the
tube, and with luck, the mushroom mycelium
is favorably selected, reaching the opposite end
first. At this point, the cultivator simply transfers
a sample of emerging mycelium from the
end of the tube to newly poured media plates.
The cultures are then labelled, sealed and ob-
* The spores of most mold fungi become distinctly pigmented at
matuiity. SomePenicillium molds are typically blue-green.Aspergillus
species range in color from black to green to yellow.
Neurospora can be pink. A few molds, such as Monilia or
Verticillium, produce white colonies. For more information on
these competitors, please consult The Mushroom Cultivator
(1983) by Stamets & Chilton.
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