4.2.4 Oxalate Production
Metal immobilization through insoluble metal oxalate formation is a process of
marked ecological significance being engaged with fungal survival, mineral formation, pathogenesis, biodeterioration, soil weathering, and metal detoxification
(Kaewdoung et al. 2016). As illustrated in Fig. 17.2, the production of oxalic acid
by fungi provides a means of immobilizing soluble metal ions, or complexes, as
insoluble oxalates decreasing bioavailability and conferring tolerance. JaroszWilkolazka and Gadd (2003) studied oxalate-producing white-rot species,
Bjerkandera fumosa, Trametes versicolor, and Phlebia radiata, and a brown-rot
species, Fomitopsis Pinicola, were used for solubilization of metals (JaroszWilkolazka and Gadd 2003). Filamentous fungi, compared with bacteria, secrete a
large number of organic acids, for example oxalic, tartaric, and citric acids. The
secreted oxalic acid can react with Pb (II) to form primarily lead oxalate and
insoluble Pb minerals. Then, the enhanced biosorption via forming a new border
of the cell wall prevents the transportation of Pb (II) into hypha (Tian et al. 2018).
5 Functional Groups on the Surface of Fungi for Heavy
Metal Removal
Features responsible for the functional group’s biosorption of metal ions are determined by Fourier-transform infrared spectroscopy (FTIR). The mechanism of
biosorption was investigated by measuring the zeta potential and by performing
FTIR, and most of the wavenumber is ranged from 400–4000 cm
À1 , and FTIR
spectra were measured on KBr pellet (Aytar et al. 2014). The bonding mechanism
between heavy metals and fungal biomass can be determined by interpreting the
FTIR absorption spectrum (Simonescu and Ferdeş 2012). For instance, from
Table 17.2 below, the fungal species consist of a common functional group to
remove heavy metals, especially
_ OH, C
_ H, and some of the species consist of
unique functional groups, namely, thiol. Uptake of metal by a fungus has been
enhanced by electrostatic attraction to anion functional groups on the cell surface,
resulting in the passive attraction of various metal cations (Tsekova et al. 2006). The
biosorption capacity of the fungal biomass of Pleurotus mutilus for biosorption of
Fe
+3 and Mn
+2 was evaluated in Table 17.2. Different functional groups, alcohol,
hydroxyl, amino, and carboxyl on biosorbent which are responsible for biosorption
of positively charged metal ion (Fe
+3 and Mn
+2 ) with negatively charged functional
groups, were reported by Madani et al. (2015). Functional groups on the biomass
surfaces can be modified by various pretreatment methods such as acid, base, and
thermal treatment (Fig. 17.3) for the effective adsorption of heavy metals. The
surface modification impacts the functional groups on the surface of biomass to
enhance the adsorption capacity of biomass (Yin et al. 2018; Kumar et al. 2019).
366
A. Ayele et al.
Metal immobilization through insoluble metal oxalate formation is a process of
marked ecological significance being engaged with fungal survival, mineral formation, pathogenesis, biodeterioration, soil weathering, and metal detoxification
(Kaewdoung et al. 2016). As illustrated in Fig. 17.2, the production of oxalic acid
by fungi provides a means of immobilizing soluble metal ions, or complexes, as
insoluble oxalates decreasing bioavailability and conferring tolerance. JaroszWilkolazka and Gadd (2003) studied oxalate-producing white-rot species,
Bjerkandera fumosa, Trametes versicolor, and Phlebia radiata, and a brown-rot
species, Fomitopsis Pinicola, were used for solubilization of metals (JaroszWilkolazka and Gadd 2003). Filamentous fungi, compared with bacteria, secrete a
large number of organic acids, for example oxalic, tartaric, and citric acids. The
secreted oxalic acid can react with Pb (II) to form primarily lead oxalate and
insoluble Pb minerals. Then, the enhanced biosorption via forming a new border
of the cell wall prevents the transportation of Pb (II) into hypha (Tian et al. 2018).
5 Functional Groups on the Surface of Fungi for Heavy
Metal Removal
Features responsible for the functional group’s biosorption of metal ions are determined by Fourier-transform infrared spectroscopy (FTIR). The mechanism of
biosorption was investigated by measuring the zeta potential and by performing
FTIR, and most of the wavenumber is ranged from 400–4000 cm
À1 , and FTIR
spectra were measured on KBr pellet (Aytar et al. 2014). The bonding mechanism
between heavy metals and fungal biomass can be determined by interpreting the
FTIR absorption spectrum (Simonescu and Ferdeş 2012). For instance, from
Table 17.2 below, the fungal species consist of a common functional group to
remove heavy metals, especially
_ OH, C
_ H, and some of the species consist of
unique functional groups, namely, thiol. Uptake of metal by a fungus has been
enhanced by electrostatic attraction to anion functional groups on the cell surface,
resulting in the passive attraction of various metal cations (Tsekova et al. 2006). The
biosorption capacity of the fungal biomass of Pleurotus mutilus for biosorption of
Fe
+3 and Mn
+2 was evaluated in Table 17.2. Different functional groups, alcohol,
hydroxyl, amino, and carboxyl on biosorbent which are responsible for biosorption
of positively charged metal ion (Fe
+3 and Mn
+2 ) with negatively charged functional
groups, were reported by Madani et al. (2015). Functional groups on the biomass
surfaces can be modified by various pretreatment methods such as acid, base, and
thermal treatment (Fig. 17.3) for the effective adsorption of heavy metals. The
surface modification impacts the functional groups on the surface of biomass to
enhance the adsorption capacity of biomass (Yin et al. 2018; Kumar et al. 2019).
366
A. Ayele et al.