ligninolytic enzymes are encoded by gene families that lead to the production of
multiple enzyme isoforms (Thurston 1994; Tuor et al. 1995; Martínez 2002).
Ligninolytic enzyme production occurs mostly during the secondary metabolism
and the ligninolytic activities are strongly induced by starvation conditions (i.e.,
nitrogen, carbohydrate, and sulfur limitation) as well as by the presence of trace
metals like Mg
2+ and Ca
2+ (Jeffries et al. 1981). Furthermore, growth conditions
(i.e., temperature) significantly affect the level of activity of ligninolytic enzymes
(Podgornik et al. 2001; Bermek et al. 2004). Additionally, the ligninolytic enzyme
production is also affected by the presence/absence of mediators or various
chemicals and by specific concentrations of metals Mn
2+ and/or Cu
2+ (Scheel
et al. 2000; Galhaup et al. 2002).
A new type of H 2 O 2 -requiring enzyme was also described in the basidiomycete
Agrocybe aegerita (Ullrich et al. 2004) and, later, in other fungi (Hofrichter and
Ullrich 2014). These proteins are heme-thiolate haloperoxidases, classified as fungal
unspecific peroxygenases (UPO, EC 1.11.2.1). Their catalytic cycle combines the
typical pathways of extracellular peroxidases and intracellular monooxygenases
(unspecific cytochrome P450 system, CYP450, EC 1.14.14.1), thus enabling them
to catalyze a wide array of reactions (Hofrichter and Ullrich 2014).
22.3 Mycoremediation and White-Rot Fungi
Fungi with contaminant-degrading capabilities are mostly wood-degrading basidiomycetes belonging to Agaricales (i.e., Stropharia rugosoannulata, Agrocybe
praecox, and Pleurotus ostreatus) and Polyporales orders (i.e., Phanerochaete
chysosporium, Trametes versicolor, Bjerkandera adusta, Irpex lacteus, etc.) (Gadd
2001; Singh 2006). In addition, several fungi belonging to the phyla Ascomycota
(i.e., Trichoderma spp.), Zygomycota (i.e., Mucor spp.), and anamorphic ascomycetes (i.e., Aspergillus spp., Penicillium spp., Paecilomyces spp.) have also demonstrated the ability to degrade contaminants (Tortella et al. 2005; Tigini et al. 2009;
Carvalho et al. 2009).
Among contaminant-degrading fungi, the group of white-rot fungi (WRFs),
which is specialized in lignin breakdown, is particularly promising in the bioremediation of contaminated matrices. Indeed, in addition to their natural substrate, these
fungi can degrade and, to some extent mineralize, a wide range of organic and
xenobiotic pollutants structurally similar to lignin such as petroleum hydrocarbons,
chlorophenols, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dioxins and furans, pesticides, herbicides, and nitroaromatic explosives
(Pointing 2001; Mougin et al. 2002; Rabinovich et al. 2004; Baldrian 2008;
Cerniglia and Sutherland 2006; Cajthaml and Svobodová 2012).
These fungi can easily penetrate into the polluted matrix thanks to their hyphal
structures and reach the less bioavailable contaminants by secreting ligninolytic
enzymes (i.e., Lac, LiP, and MnP) into the extracellular environment. As already
mentioned, these oxidases exhibit very low substrate specificity and can attack the
22 Mycoremediation of Contaminated Soils
447
multiple enzyme isoforms (Thurston 1994; Tuor et al. 1995; Martínez 2002).
Ligninolytic enzyme production occurs mostly during the secondary metabolism
and the ligninolytic activities are strongly induced by starvation conditions (i.e.,
nitrogen, carbohydrate, and sulfur limitation) as well as by the presence of trace
metals like Mg
2+ and Ca
2+ (Jeffries et al. 1981). Furthermore, growth conditions
(i.e., temperature) significantly affect the level of activity of ligninolytic enzymes
(Podgornik et al. 2001; Bermek et al. 2004). Additionally, the ligninolytic enzyme
production is also affected by the presence/absence of mediators or various
chemicals and by specific concentrations of metals Mn
2+ and/or Cu
2+ (Scheel
et al. 2000; Galhaup et al. 2002).
A new type of H 2 O 2 -requiring enzyme was also described in the basidiomycete
Agrocybe aegerita (Ullrich et al. 2004) and, later, in other fungi (Hofrichter and
Ullrich 2014). These proteins are heme-thiolate haloperoxidases, classified as fungal
unspecific peroxygenases (UPO, EC 1.11.2.1). Their catalytic cycle combines the
typical pathways of extracellular peroxidases and intracellular monooxygenases
(unspecific cytochrome P450 system, CYP450, EC 1.14.14.1), thus enabling them
to catalyze a wide array of reactions (Hofrichter and Ullrich 2014).
22.3 Mycoremediation and White-Rot Fungi
Fungi with contaminant-degrading capabilities are mostly wood-degrading basidiomycetes belonging to Agaricales (i.e., Stropharia rugosoannulata, Agrocybe
praecox, and Pleurotus ostreatus) and Polyporales orders (i.e., Phanerochaete
chysosporium, Trametes versicolor, Bjerkandera adusta, Irpex lacteus, etc.) (Gadd
2001; Singh 2006). In addition, several fungi belonging to the phyla Ascomycota
(i.e., Trichoderma spp.), Zygomycota (i.e., Mucor spp.), and anamorphic ascomycetes (i.e., Aspergillus spp., Penicillium spp., Paecilomyces spp.) have also demonstrated the ability to degrade contaminants (Tortella et al. 2005; Tigini et al. 2009;
Carvalho et al. 2009).
Among contaminant-degrading fungi, the group of white-rot fungi (WRFs),
which is specialized in lignin breakdown, is particularly promising in the bioremediation of contaminated matrices. Indeed, in addition to their natural substrate, these
fungi can degrade and, to some extent mineralize, a wide range of organic and
xenobiotic pollutants structurally similar to lignin such as petroleum hydrocarbons,
chlorophenols, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dioxins and furans, pesticides, herbicides, and nitroaromatic explosives
(Pointing 2001; Mougin et al. 2002; Rabinovich et al. 2004; Baldrian 2008;
Cerniglia and Sutherland 2006; Cajthaml and Svobodová 2012).
These fungi can easily penetrate into the polluted matrix thanks to their hyphal
structures and reach the less bioavailable contaminants by secreting ligninolytic
enzymes (i.e., Lac, LiP, and MnP) into the extracellular environment. As already
mentioned, these oxidases exhibit very low substrate specificity and can attack the
22 Mycoremediation of Contaminated Soils
447