6 Wood Discoloration

3.4 Temperature 67
puteana, Gloeophyllum trabeum, and Donkioporia expansa may survive as
arthrospores (Huckfeldt et al. 2005).
3.4
Temperature
With respect to the temperature, Table 3.8 shows the cardinal points for some
wood fungi. A comprehensive investigation was completed in 1933 grouping
the species into low-temperature (optimum 24 ◦ Candbelow),intermediatetemperature
(optimum between 24 and 32 ◦ C), and high-temperature group
(optimum above 32 ◦ C) (Humphrey and Siggers 1933). For three species, e.g.,
Gloeophyllum sepiarium, minimum, and maximum temperatures were already
determined (Lindgren 1933). It has to be considered, however, that considerable
differences can exist between isolates of a species (Table 3.11).
Generally, it applies to wood fungi: The minimum is usually at 0 ◦ C, because
below the freezing point there is no liquid water available necessary for
metabolism. Exceptions of growth below 0 ◦ C are possible, if the freezing point
is decreased, e.g., by trehalose and glycerol or other polyhydric alcohols as
anti-freeze agents which prevent ice-crystal formation within the hypha (Jennings
and Lysek 1999). In some blue-stain and mold fungi, the lower limit for
mycelial growth is at −7 to −8 ◦ C (Reiß 1997). Above the lower limit, the “reaction
speed-temperature rule” begins to take effect, as in a certain temperature
range, enzyme activity runs two to four times faster by increasing the temperature
of about 10 ◦ C(Q10 value). Frequently, the optimum lies, depending on the
species (and isolate) between 20 and 40 ◦ C. Psychrophilic fungi have their optimum
below 20 ◦ C, mesophilic species between 20 and 40 ◦ C and thermophilic
species over 40 ◦ C. Thermotolerant fungi, e.g., Phanerochaete chrysosporium
and other fungi growing in wood chip piles, prefer the mesophilic range, tolerate
however still 50 ◦ C. The maximum for mycelial growth and wood damage
by most wood fungi is often at 40–50 ◦ C, because then the protein (enzyme)
denaturing by heat takes effect. Fungi, however, may exhibit a change in gene
expression, which leads to the synthesis of “heat-shock proteins (hsp)”. The
hsps appear to prevent and repair general damage, denaturation and aggregation
of other cellular proteins, as they are not only induced by heat, but also by
heavy metals and oxidants (Jennings and Lysek 1999).
Serpula lacrymans possesses a characteristic, which can be used for identification.
With the optimum of about 20 ◦ C, slight growth still at 26–27 ◦ C, and
growth stop at 27–28 ◦ C, the fungus differs from the other indoor wood decay
fungi, like the Cellar fungus and the white polypores, as well as from other
Serpula species, because, e.g., S. himantioides still grows at 31 ◦ C. There are,
however wild Himalayan isolates of S. lacrymans that showed slight growth
at 32 ◦ C (Palfreyman and Low 2002). In addition, in S. lacrymans also the
www.taq.ir