Volume 16, Number 1
Feb 1992

What it Takes to Activate a Fungal Spore:

An Excerpt from the Guldbeck Memorial Lecture

[Editor's note: The author gave the Per Guldbeck Memorial Lecture, entitled "About Time," at the 17th Annual Conference of the IIC-CG in Vancouver, May 25, 1991. The last section of that lecture is reprinted below, with permission, from the IIC-CG Bulletin. v.16 #3, September 1991, p 9-16.

[References 23 and 24 have been renumbered I and 2, and a short glossary, made up in part of definitions provided in other sections of the lecture, has been added following the references./

Frugal Fungi Fact

. . . Organisms can go into near metabolic arrest to aid dissemination. The frugal fungi conidia or spores do this by dehydration.l This is why I call them the frugal fungi. Air always contains thousands of fungi spores or conidia, in a metabolically inactive reversible rest period which enables them to survive adverse environmental conditions.

When spores fall on wet materials, the majority of spores do not germinate. They need, in addition to water, a physical or chemical activator.1 This is why all damp surfaces are not covered with fungi growth after a rain or dew. If a spore has been activated but dries up, the spore will remain activated and as soon as conducive environmental conditions arise the spore germinates. This is important information to conservators, because many of the chemicals used in treatments such as alcohols, acetone, surfactants, and detergents act as activators.2 Acid and alkaline treatments also cause activation. This suggests that we may be setting up potential fungi hazards. Even ethylene glycol, which is a by-product of ethylene oxide fumigation, activates fungi spores. It is probably the presence of this spore activator in fumigated parchments which appears to make them more prone to support fungi growth. This is indeed an exciting topic and a barren field waiting for future research. We have treated surface fungi growth much too simplistically in the past. We have looked at growth parameters of the mycelium but have not looked holistically at all stages, spore dormancy, activation and germination, and then mycelium growth. I am sure that in the near future we will find appropriate methods of control, not only in growth parameters but in preventing spore activation and germination.

Fungi are often thought to be xerophyllic, able to germinate under low water conditions. Relative to other fungi, some may be xerophyllic, but the moisture level in materials required for growth is always high. The so-called xerophyllic fungi have glycols in their cell which have a lower water activity than most fungi can tolerate but still it is high. Generally speaking, it is equivalent to the equilibrium moisture content of absorbent materials held at 80% RH at room temperature.

References

1. T.G. Cole and G. Kendrick. 1981. Biology of Conidial Fungi. Vol. 2. Academic Press.

2. D.A. Cotter. 1981. "Spore Activation." In The Fungal Spore. G. Turian and H.R. Hohl, eds. Academic Press. Pp. 385-411.

Glossary

conidium: Broadly, any asexual spore not borne within an enclosing structure.

equilibrium moisture content: A measure of the amount of water in material as a percent of dry weight of the material at a specific temperature and RH. EMC varies with changes in temperature and RH. At constant RH a piece of cold cotton will have a higher EMC than when hot, and at constant temperature, the higher the RH the higher the EMC.

hypha (pl. hyphae): One of the individual threads that make up the mycelium of a fungus, and increase by apical growth.

mycelium: The mass of interwoven hyphae that in the larger forms of the fungi (as the mushrooms) forms cobwebby filaments penetrating the substrate but in many smaller fungi (as in most parasitic forms) is invisible to the naked eye, usually producing its spore fruits on the surface .

spore: A minute unicellular reproductive or resistant resting body that is often adapted to survive unfavorable environmental conditions and to produce a new vegetative individual when these conditions alter.

water activity: The water vapor pressure in the material as a result of the solutes dissolved in it as compared to the vapor pressure of pure water.