avoids the build up of cellobiose that would inhibit the cellobiohydrolases activity.
Thus the entire system has to operate in a well-timed paced manner in order to get
an effective cellulose degradation process (Lynd et al. 2002). The lignocellulose
degradation process is much more complicated in reality, mainly due to presence
of lignin that surrounds the cellulose chains and may be the reason why the most
effective cellulose degrading organisms possess several enzymes for each activity,
for example, Cellulomonas thermocellum has at least nine endoglucanases, four
exoglucanases, and five hemicellulases (Kumar et al. 2008).
7.3 Lignocellulose Degrading Organisms
Bacteria and fungi are able to degrade the amorphous soluble cellulose in a rapid
and efficient way (Lynd et al. 2002), but the ability to degrade crystalline cellulose
is restricted to very specialized cellulose degrading microorganisms (Coughlan
and Mayer 1992). Cellulose degrading bacteria belong mainly to the anaerobic
Clostridium genus or aerobic Cellulomonas genus of Gram-positive bacteria and
some Gram-negative anaerobic Fibrobacteria and Mixobacteria genus (Glazer and
Nikaido 1995).
The best lignocellulose degraders are fungi that belong to soft rot fungi
(Ascomycetes) and brown or white rot fungi (Basidiomycetes) groups. Each group
produces a collection of dedicated enzymes for the degradation of specific plant
polysaccharides; along with this there are many families of glycoside hydrolases,
esterases, and lyases. Many of these families can have multiple catalytic activities,
and many of these activities show complementary activity over the same substrates
(Dias et al. 2004; Cantarel et al. 2009; Coutinho et al. 2009).
Filamentous fungi that has an ecological niche as saprobes has the enzymatic
tools to degrade lignocellulosic biomass but show some specialization; for
example, A. niger has a large number of enzymes for pectin degradation, while
Phanerochaete chrysosporium shows a very specialized enzymatic kit for lignin
degradation. This specialization can be explored to discover new enzymes with
novel activities or more suitable reaction conditions as resistance to higher temperatures or product accumulation, as is required to the efficient degradation of the
complex polysaccharides of plant biomass. Degradation of crude biomass is a very
complex to achieve, enzyme mix necessary for the complete degradation of plant
biomass depends on the type of biomass, growth conditions, and pretreatment used
in the said material. In order to improve the efficiency of both lignocellulose
degrading system and organisms it is necessary to develop several strategies that
go from a better understanding of the lignocellulose degradation to the improvement of known strains or the discovery and use of new lignocellulose degrading
organisms (Saha and Cotta 2010; Van den Brink and de Vries 2011).
238
S. de J. Romero-Gómez
Thus the entire system has to operate in a well-timed paced manner in order to get
an effective cellulose degradation process (Lynd et al. 2002). The lignocellulose
degradation process is much more complicated in reality, mainly due to presence
of lignin that surrounds the cellulose chains and may be the reason why the most
effective cellulose degrading organisms possess several enzymes for each activity,
for example, Cellulomonas thermocellum has at least nine endoglucanases, four
exoglucanases, and five hemicellulases (Kumar et al. 2008).
7.3 Lignocellulose Degrading Organisms
Bacteria and fungi are able to degrade the amorphous soluble cellulose in a rapid
and efficient way (Lynd et al. 2002), but the ability to degrade crystalline cellulose
is restricted to very specialized cellulose degrading microorganisms (Coughlan
and Mayer 1992). Cellulose degrading bacteria belong mainly to the anaerobic
Clostridium genus or aerobic Cellulomonas genus of Gram-positive bacteria and
some Gram-negative anaerobic Fibrobacteria and Mixobacteria genus (Glazer and
Nikaido 1995).
The best lignocellulose degraders are fungi that belong to soft rot fungi
(Ascomycetes) and brown or white rot fungi (Basidiomycetes) groups. Each group
produces a collection of dedicated enzymes for the degradation of specific plant
polysaccharides; along with this there are many families of glycoside hydrolases,
esterases, and lyases. Many of these families can have multiple catalytic activities,
and many of these activities show complementary activity over the same substrates
(Dias et al. 2004; Cantarel et al. 2009; Coutinho et al. 2009).
Filamentous fungi that has an ecological niche as saprobes has the enzymatic
tools to degrade lignocellulosic biomass but show some specialization; for
example, A. niger has a large number of enzymes for pectin degradation, while
Phanerochaete chrysosporium shows a very specialized enzymatic kit for lignin
degradation. This specialization can be explored to discover new enzymes with
novel activities or more suitable reaction conditions as resistance to higher temperatures or product accumulation, as is required to the efficient degradation of the
complex polysaccharides of plant biomass. Degradation of crude biomass is a very
complex to achieve, enzyme mix necessary for the complete degradation of plant
biomass depends on the type of biomass, growth conditions, and pretreatment used
in the said material. In order to improve the efficiency of both lignocellulose
degrading system and organisms it is necessary to develop several strategies that
go from a better understanding of the lignocellulose degradation to the improvement of known strains or the discovery and use of new lignocellulose degrading
organisms (Saha and Cotta 2010; Van den Brink and de Vries 2011).
238
S. de J. Romero-Gómez