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Volume 8 Part 1 Article 71
Year 1972
Title: Experiments and Comments on the Action of Bacteria on Sporophore Initiation in Agaricus bisporus
Author: G. Eger
Abstract:
From 1959 to 1962 I published some facts and hypotheses on the action of
bacteria on sporophore initiation in the cultivated mushroom:
- 1. Agaricus bisporus usually does not fruit under conditions which exclude
microbes to a high degree.
- 2. The microflora in casing soil from cultures with a very good crop differs
from that from cultures with poor or no fructification.
Among the former,
bacterial colonies are present which are able to inhibit mycelial growth and
to induce primordia.
Not a single fungal isolate revealed similar effects.
- 3. In freshly prepared casing soil, inducing bacteria seem not to be present in
high numbers.
The inducing effect of soil increases while resting on
mushroom beds.
Therefore we assume that the bacteria propagate after
casing.
- 4. Equally an improvement of the casing layer takes place if inorganic material
is used and an air space of 1 to 4 cm is left between the mycelium and the
casing.
Thus the microbes in question should be able to feed on volatile
metabolites of the fungus.
- 5. Growing mycelia of Agaricus bisporus produce a volatile metabolite (or
metabolites) with antibiotic effects.
The casing layer may prevent inducing
organisms from contact with high concentrations of the volatile inhibitor(s)
and allow rapid propagation.
However, in order to produce primordia, a
fungal hypha has to come into close contact with accumulations of inducing
bacteria.
- 6. Mixtures of soil bacteria which are able to induce sporophores may be
propagated in nutrient broth.
Sterile filtrates (Seitz-EK-filters) of such
cultures are without effect.
- 7. Different strains of the cultivated mushroom differ in their sensitivity to
bacterial inducers.
Strain 310a (selected by Dr Gerda Pritsche) responds
very easily as compared with a great number of other strains, especially 71a.
- 8. Different absorbing materials have been tried as a casing under aseptic
conditions.
Only active charcoal gave even results excluding interpretation
as chance contamination.
Thus our findings were in contrast to older repoits of fruiting under aseptic
conditions and have been criticized.
Taking both seriously we examined working
conditions and arguments ol the individual authors.
According to technical
progress our working conditions have been superior to those of prior investigators.
Schisler's (1957) 'fruiting under sterile conditions' - two fertile flasks out
720 Eger
of a total of six - may better be interpreted as chance contamination.
Koch's
(1958) sterilization procedures did not suffice - as has been shown already in
1961. Lockard & Kneebone (1962) reported again on fruiting under sterile
conditions in erlenmeyer flasks provided with continuous air flow.
In similar
experiments in normal laboratory rooms we could not ensure sterility over a
period of several weeks by cotton filters.
Tschierpe & Sinden (1964) presumed
that autoclaving of our casing soil produces inhibitory substances.
We are sure
that this is not the case.
Autoclaved inorganic materials as pumice, perlite,
vermiculite, quartz sand and three different types of plastic foam equally failed
to induce primordia under aseptic conditions.
The arguments of Tschierpe &
Sinden have been refuted additionally by Long & Jacobs (1968) who stated:
'The failure to induce sporophore formation in our experiments employing
sterilized substrates does not appear to be linked with toxic materials produced
by autoclaving casing materials.
Propylene oxide sterilized casing or autoclaved
casing washed repeatedly with water by centrifugation under aseptic conditions,
failed to promote initiation'.
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