Mold Spore Viability
Over what
period of time are mould spores viable? I am thinking of mould
spores in old documents or books. -Margot,
Aberdeen, Scotland
Unfortunately mold growth in/on old
documents and books is a common problem. It is often addressed by
the use of special preservation techniques (use of biocides and
environmental control) to prevent active mold growth from
reoccurring.
Paper, leather, binder adhesives,
etc. are good nutrient sources. If combined with elevated relative
humidity (> 70%) over a period of weeks or wetness and a favorable
temperature >40 oF (5oC) and a highly probable
chance deposition of a viable spore or hyphal fragment one has an
active infestation of the document or book. Once infested it is a
real challenge to completely eradicate (in the sense of completely
killing all fungal material) the fungus/fungi present by the use of
a biocide/biocides. This is why control of environmental conditions
in special collections area of libraries is so important.
Continuously maintaining relative humidity below 60% prevents
infestations from reoccurring even if viable fungal matter is still
present.
Note that your question was about
the viability of fungal species, and I just referred to fungal
matter. The latter reflects the fact that more than spores may be
involved in the infestation/re-infestation of a document or book.
Most fungal species reproduce by
producing spores that are designed to be carried by air currents and
dispersed to a new substrate which may then be colonized/infested.
Some fungal species produce large numbers of spores (tens of
thousands) even from a small infestation (diameter of a coin).
Others may produce relatively few. A variety of environmental
factors affect spore production (i.e. unfavorable growth
conditions). Yes, more spores can be produced when a fungal mass is
exposed to harmful environmental conditions such as dryness, and
ultra violet light (from sunlight, etc.).
Such environmental conditions can
not only induce sporulation but also adversely affect the spores and
the organism that produced them (reduce their viability). Because
of exposure to dry conditions and sunlight, mold spores from common
fungi (such as those from the genera Penicillium and
Aspergillus that are known to infest documents books), lose
their viability in a matter of hours to days.
Fungi, of course, have evolved
mechanisms to ensure that the species survives even in relatively
harsh environments. Many produce sclerotia which are dark fungal
masses that persist for years if not decades and then germinate
under suitable environmental conditions. Sclerotia are produced by
a number of Aspergillus species,organisms commonly observed
to infest paper products. I often see what I believe to be
Aspergillus sclerotia in air samples from environments where fungal
organisms have been subject to exposure to biocides and/or dry
conditions.
Back to your question. For asexual
spores commonly produced by Penicillium and Aspergillus,
I would expect a 90% reduction in the number of viable spores in a
matter of days under normal environmental conditions. In dark humid
environments, such spores would remain viable for months or longer.
If the organism produces sclerotia, then the organism is potentially
viable for decades or more in what appears to be in an inactive
state.
August 11,2006
