also the nutrient cycling. They encompass various organic and inorganic pollutants
(Walker et al. 2006): petroleum hydrocarbons, halogenated solvents, chlorinated
aromatic hydrocarbons, explosives, dioxins, endocrine disrupting compounds, herbicides, pesticide, heavy metals, and radionuclides. These pollutants are commonly
present in the environment in the form of a complex mixture, making the remediation of these co-contaminated sites a challenge to face.
Conventional remediation technologies based on physical and chemical
approaches are still the most applied ones for the disposal of hazardous chemicals
despite the fact that they are not sustainable in terms of both cost and the environmental impact. Thus, biological treatments are being considered as a valid alternative
to traditional remedial strategies.
A specific branch of bioremediation, called mycoremediation, has been arousing
real interest in recent years. This technology is based on the use of fungi for the
remediation of polluted soils or other solid–liquid matrices.
Fungi are a diverse group of microorganisms ubiquitously present in natural
ecosystems and able to thrive in a variety of habitats. They are the major decomposers of complex biomaterials. Saprotrophic fungi in particular are responsible for
biomass decomposition.
Among saprotrophic organisms, wood decay fungi evolved an efficient
non-specific extracellular enzymatic system for degradation of complex heterogeneous polymers, such as lignocellulose and chitin. Owing to the production of such
lignocellulolytic enzymes, they can transform a wide array of organic substrates
including organic pollutants that are inaccessible to most of prokaryotes.
Due to these capabilities, ligninolytic fungi (LFs) are considered to play a key role
in the biodegradation processes of recalcitrant organic pollutants in a number of
contaminated matrices.
22.2 Ligninolytic Fungi and Their Enzymes
Ligninolytic fungi variously secrete one or more of three main extracellular lignindegrading enzymes, namely lignin peroxidase (LiP, E.C. 1.11.1.14), manganesedependent peroxidase (MnP, E.C. 1.11.1.13), and laccase (Lac, E.C. 1.10.3.2) (Tuor
et al. 1995).
However, novel manganese-independent peroxidase activity and other versatile
peroxidase activities have been more recently found in some genera of white-rot
fungi (Heinfling et al. 1998; Camarero et al. 1999; Ruiz-Dueñas et al. 2001).
Moreover, other enzymes associated with lignin-degrading enzymes are produced by LFs: glyoxal oxidase (E.C. 1.2.3.5), superoxide dismutase
(E.C. 1.15.1.1), glucose oxidase (E.C. 1.1.3.4), aryl alcohol oxidase (E.C. 1.1.3.7),
and cellobiose dehydrogenase (E.C. 1.1.99.18). They produce H 2 O 2 , which is
essential for the catalytic cycle of peroxidases (LiP and MnP), or degrade the
non-phenolic substructures of lignin by the formation of reactive hydroxyl radicals
•
OH (Hatakka 2001; Leonowicz et al. 2001; Lundell et al. 2010). All the three major
446
T. Stella
(Walker et al. 2006): petroleum hydrocarbons, halogenated solvents, chlorinated
aromatic hydrocarbons, explosives, dioxins, endocrine disrupting compounds, herbicides, pesticide, heavy metals, and radionuclides. These pollutants are commonly
present in the environment in the form of a complex mixture, making the remediation of these co-contaminated sites a challenge to face.
Conventional remediation technologies based on physical and chemical
approaches are still the most applied ones for the disposal of hazardous chemicals
despite the fact that they are not sustainable in terms of both cost and the environmental impact. Thus, biological treatments are being considered as a valid alternative
to traditional remedial strategies.
A specific branch of bioremediation, called mycoremediation, has been arousing
real interest in recent years. This technology is based on the use of fungi for the
remediation of polluted soils or other solid–liquid matrices.
Fungi are a diverse group of microorganisms ubiquitously present in natural
ecosystems and able to thrive in a variety of habitats. They are the major decomposers of complex biomaterials. Saprotrophic fungi in particular are responsible for
biomass decomposition.
Among saprotrophic organisms, wood decay fungi evolved an efficient
non-specific extracellular enzymatic system for degradation of complex heterogeneous polymers, such as lignocellulose and chitin. Owing to the production of such
lignocellulolytic enzymes, they can transform a wide array of organic substrates
including organic pollutants that are inaccessible to most of prokaryotes.
Due to these capabilities, ligninolytic fungi (LFs) are considered to play a key role
in the biodegradation processes of recalcitrant organic pollutants in a number of
contaminated matrices.
22.2 Ligninolytic Fungi and Their Enzymes
Ligninolytic fungi variously secrete one or more of three main extracellular lignindegrading enzymes, namely lignin peroxidase (LiP, E.C. 1.11.1.14), manganesedependent peroxidase (MnP, E.C. 1.11.1.13), and laccase (Lac, E.C. 1.10.3.2) (Tuor
et al. 1995).
However, novel manganese-independent peroxidase activity and other versatile
peroxidase activities have been more recently found in some genera of white-rot
fungi (Heinfling et al. 1998; Camarero et al. 1999; Ruiz-Dueñas et al. 2001).
Moreover, other enzymes associated with lignin-degrading enzymes are produced by LFs: glyoxal oxidase (E.C. 1.2.3.5), superoxide dismutase
(E.C. 1.15.1.1), glucose oxidase (E.C. 1.1.3.4), aryl alcohol oxidase (E.C. 1.1.3.7),
and cellobiose dehydrogenase (E.C. 1.1.99.18). They produce H 2 O 2 , which is
essential for the catalytic cycle of peroxidases (LiP and MnP), or degrade the
non-phenolic substructures of lignin by the formation of reactive hydroxyl radicals
•
OH (Hatakka 2001; Leonowicz et al. 2001; Lundell et al. 2010). All the three major
446
T. Stella