11.3.3 Transfer Factor and Metal Accumulation in Sclerotia
The transfer factor (TF) of trace metals from soils to mushrooms (A. bisporus) was
calculated by Sithole et al. (2017). More specifically, Vinichuk (2013) defined the
bioconcentration ratio (BCR) of metal as the concentration of the element in a
specific fraction, for example, the concentration of a specific element in the fungal
mycelium and fruiting bodies divided by the concentration of the elements in bulk
soil. In this study, we calculated the TF as the ratio of the concentration of trace
metals in sclerotia to the content present in the soil, according to Eq. (11.2).
TF ¼ C sclerotia =C soil
ð11:2Þ
where TF represents the transfer factor of a particular metal, C sclerotia is the concentration of that metal in the sclerotia ( μg g
À1 ), and C soil is the metal content in the soil
(ppm).
Transfer factors (TFs) are presented in Table 11.4 and Fig. 11.5. The TFs of Al
and Ca from the soil to sclerotia grains were 0.19 and 0.23 in Japanese samples, 0.02
and 0.74 in Mongolian samples, whereas the TF of Fe was 0.19 and 0.24 for soil
samples from Mongolia and Japan, respectively. The TFs of Pb, Zn, and As ranged
from 0.49 to 2.43 in Japanese samples and from 0.45 to 3.08 in Mongolian samples.
The TF of Cu was 6.34 Æ 1.83 in Mongolian samples, significantly different from
that in Japanese sclerotia grains (1.66 Æ 1.57); the TFs of Al and Ca also differed
significantly between sclerotia from Mongolia and Japan. The TFs of Fe, Pb, Zn, and
As were similar across Japanese and Mongolian samples (Fig. 11.5).
Fungi frequently show a higher affinity than other microbial taxa for metal ions
and can accumulate metals from their external environment by means of various
physicochemical and biological mechanisms (Khoo and Ting 2000; Cabuk et al.
2004; Preetha and Viruthagiri 2005). Sclerotial walls consist of a highly resistant
melanin-like pigment, which plays an important role in the resistance of sclerotia to
chemical and biological degradation (Chen et al. 2007). Natural and synthetic
melanins have the capacity to bind metal ions in vivo and in vitro (Bruenger et al.
1967; Larsson and Tjalve 1978) and are similar to cation exchange resins (Bruenger
et al. 1967; Froncisz et al. 1980). Several studies refer to carboxyl groups as the main
binding sites (Larsson and Tjalve 1978) but this may depend on the pH and type of
melanin. Some forms of melanin, at pH <5, form Cu complexes with carboxyl
groups but at pH >6, phenolic hydroxyl groups are the main Cu ligands (Froncisz
et al. 1980).
Response of fungi on Cu toxicity was confirmed by Stokes and Lindsay (1979), in
which Penicillium ochro-chloron was found growing in an electroplating bath with
Cu
2+ levels in excess of 5000 mg L
À1 . Crusberg (2004) studied fungal beads;
spherical structures incubated from fungal spores and mantled by mycelia of
P. ochro-chloron (ATCC 26741), in liquid culture (Cu(II) phosphate and Cu
(II) oxalate salts) and revealed that oxalate is released from the fungal cells and
forms a precipitate with Cu when the Ksp (solubility product constant) is exceeded.
11 Melanized Sclerotia Grains from Mongolian Steppe Forest Soils
203
The transfer factor (TF) of trace metals from soils to mushrooms (A. bisporus) was
calculated by Sithole et al. (2017). More specifically, Vinichuk (2013) defined the
bioconcentration ratio (BCR) of metal as the concentration of the element in a
specific fraction, for example, the concentration of a specific element in the fungal
mycelium and fruiting bodies divided by the concentration of the elements in bulk
soil. In this study, we calculated the TF as the ratio of the concentration of trace
metals in sclerotia to the content present in the soil, according to Eq. (11.2).
TF ¼ C sclerotia =C soil
ð11:2Þ
where TF represents the transfer factor of a particular metal, C sclerotia is the concentration of that metal in the sclerotia ( μg g
À1 ), and C soil is the metal content in the soil
(ppm).
Transfer factors (TFs) are presented in Table 11.4 and Fig. 11.5. The TFs of Al
and Ca from the soil to sclerotia grains were 0.19 and 0.23 in Japanese samples, 0.02
and 0.74 in Mongolian samples, whereas the TF of Fe was 0.19 and 0.24 for soil
samples from Mongolia and Japan, respectively. The TFs of Pb, Zn, and As ranged
from 0.49 to 2.43 in Japanese samples and from 0.45 to 3.08 in Mongolian samples.
The TF of Cu was 6.34 Æ 1.83 in Mongolian samples, significantly different from
that in Japanese sclerotia grains (1.66 Æ 1.57); the TFs of Al and Ca also differed
significantly between sclerotia from Mongolia and Japan. The TFs of Fe, Pb, Zn, and
As were similar across Japanese and Mongolian samples (Fig. 11.5).
Fungi frequently show a higher affinity than other microbial taxa for metal ions
and can accumulate metals from their external environment by means of various
physicochemical and biological mechanisms (Khoo and Ting 2000; Cabuk et al.
2004; Preetha and Viruthagiri 2005). Sclerotial walls consist of a highly resistant
melanin-like pigment, which plays an important role in the resistance of sclerotia to
chemical and biological degradation (Chen et al. 2007). Natural and synthetic
melanins have the capacity to bind metal ions in vivo and in vitro (Bruenger et al.
1967; Larsson and Tjalve 1978) and are similar to cation exchange resins (Bruenger
et al. 1967; Froncisz et al. 1980). Several studies refer to carboxyl groups as the main
binding sites (Larsson and Tjalve 1978) but this may depend on the pH and type of
melanin. Some forms of melanin, at pH <5, form Cu complexes with carboxyl
groups but at pH >6, phenolic hydroxyl groups are the main Cu ligands (Froncisz
et al. 1980).
Response of fungi on Cu toxicity was confirmed by Stokes and Lindsay (1979), in
which Penicillium ochro-chloron was found growing in an electroplating bath with
Cu
2+ levels in excess of 5000 mg L
À1 . Crusberg (2004) studied fungal beads;
spherical structures incubated from fungal spores and mantled by mycelia of
P. ochro-chloron (ATCC 26741), in liquid culture (Cu(II) phosphate and Cu
(II) oxalate salts) and revealed that oxalate is released from the fungal cells and
forms a precipitate with Cu when the Ksp (solubility product constant) is exceeded.
11 Melanized Sclerotia Grains from Mongolian Steppe Forest Soils
203