Mycology notes
Fungi are one of the main groups of microorganisms that degrade starch and other plant materials in soils. The working notes on this page are an informal starting point for learning about the taphonomy of starch in soils. Eventually, we hope to develop a test system that can be used to learn about the survival or non-survival of intact and degraded starch in archaeological contexts.
At the National Museum of Ethnology, Osaka, we have started by using starch and paper filters to isolate and transfer a crude culture of an unidentified soil fungus from an organically managed vegetable garden in Katsura, Kyoto. We suspended a small sample of garden soil in water, centrifuged this very lightly in a microcentrifuge, and then used the brown supernatant to innoculate wet filters on which cycad starch had been sprinkled (upper surface only).
The filters were incubated in sealed petri dishes at 26 degrees C. for approximately one week. Only one of the set of replicates developed obvious colonies, with a blue or violet-blue colour. Spores from this filter were then transferred to a new set of filters with starch, and new colonies were established. At this stage, there has been no regeneration from a single spore only, so we may have a mixture of fungal lines here, unless the original soil sample contained only a single colony (this might happen if spores are produced apomictically, or if only mycelia were isolated in the supernatant, or if the fungus develops large vegetative colonies in the ground, and only produces spores when transferred to suitable in vitro conditions, or after soils have warmed up in spring and summer).
The fungus has branching hyphae and produces spores close to the filter surface (unlike Penicillium bread mold, which produces spores on raised spore-bearing heads, above the filter. The hyphae have been seen attacking and degrading large clumps of raw starch extracted from the test filters.
Our aim now is to learn if this fungus can be stably (and safely) maintained as a test strain for degrading starch under controlled and partially-controlled conditions.. Until it is fully identified, we will call it the Katsura Blue (KB) wildtype.
After we have obtained single colonies, and have plated these for a number of generations, we will have to assume that some kind of selection and domestication has taken place. We will only use the wildtype designation for the initial unpurified isolate (to be stored).
Key questions (any answers or comments from experts would be welcome)
1. How long can fungal spores remain viable, under what conditions?
2. What is the likelihood of accidentally isolating a fungus that is dangerous to handle? Our isolate seems relatively docile compared to ordinary bread-mould, and I will avoid inhaling the spores as much as possible, since the spres of any mould can be allergenic, it seems).
3. What simple staining methods can be used with bright-field light microscopy to help visualise the vegetative and spore bearing structures? At the moment we do not have a phase-contrast microscope, but this wwould be useful for looking at the fungi without any staining.
4. What procedures are usually used for the international exchange of non-pathenogenic fungal strains used for research?
5. How can it be established that a fungus is non-pathenogenic, if it has not been identified? Can we assume that a starch-degrading, saprophytic, aerophillic soil fungus is not a danger to either living crops or people or animals?
6. Can we isolate the same fungus repeatedly from our original garden site? Is KB common in Japan and elsewhere, or is it only locally distributed, on the geographical scale of one garden, or one river bank, or one river basin?