Keywords EndophyteLaccaseBiobleachingBiopulpingBiorefinery
Screening
12.1 Introduction
Wood is the main renewable material on Earth, and primarily composed of lignin,
cellulose, and hemicellulose (Higuchi 1997 ). Lignin provides mechanical resistance
to the plant. Lignin complex polymer with a three-dimensional structure consisting
guaiacyl (G), p-hydroxyphenyl (H), syringyl (S), and phenylpropanoid as compo-
nents. The unit of lignin is derived from the hydroxycinnamyl alcohols
(p-coumaryl, coniferyl, and sinapyl alcohols), which gives rise to variants of C–C
and ether bonds subunits (Martínez et al. 2009 ). Very few organisms are able to
degrade lignin, due to its chemical complexity and recalcitrance (Martínez et al.
2005 ). Degradation of lignin becomes a central issue in biorefinery processes, such
as in the production of ethanol and cellulose-based papers (Cañas and Camarero
2010 ). In the plant cell wall, lignin is intimately associated to carbohydrates
(hemicellulose and celluloses) to prevent easy hydrolysis for bioethanol production.
Thus, a step as pre-treatment (mainly physical or physico-chemical methods) is
necessary for increasing fermentable sugars for hydrolysis step (Salvachúa et al.
2011 ; Kataaria et al. 2013 ; Ofori-Boateng and Lee 2013 ). Regarding paper pulp
manufacture, the process basically consists in the separation (chemically or
mechanically) of lignin fromfibers. After that, residual lignin in pulps are removed
by oxidative bleaching reactions, including totally chlorine-free (TCF) bleaching
sequences (Fillat and Roncero 2010 ; Sixta 2006 ; Fillat and Roncero2009b).
Biotechnological processes could provide efficient and eco-friendly biocatalysts
for lignin modification or removal (Cañas and Camarero 2010 ). Bacteria and fungi
are capable of competently depolymerizing and mineralizing lignin (Martínez et al.
2005 ; Kunamneni et al. 2007 ). Wood-decaying fungi can secrete extracellular
enzymes related to lignin degradation, developing a complex system involving
reductases, oxidases, peroxidases, mediators, low molecular weight compounds,
etc. (Martínez et al. 2005 ). Laccases are the oxidoreductases most studied to be
applied in biotechnological processes; these enzymes oxidize phenol and other
compounds of aromatic nature (Cañas and Camarero 2010 ). Basidiomycota is
recognized as the most relevant phylum secreting laccases. However, there are
species within ascomycota, such asMyceliophthora thermophila, which also pro-
duce ligninolytic enzymes with high industrial interest due to thermal stabilities and
activities at higher pH (Ibarra et al. 2006 ). In the industrial applications, the ability
of ligninolytic fungi and their oxidoreductases enzymes (laccases and peroxidases)
to alter or remove lignin are eco-friendly schemes for utilization of renewable
lignocellulosic feedstocks. Various workers have observed that these fungi and their
enzymes act for pre-treatment steps to enhance enzymatic hydrolysis of
262 Ú. Fillat et al.