3.3
Microbial Enzymology of Biofuel Production Including
Thermophiles
Enzyme constitutes one of the vital bioproducts and finds its utility in many
technological sectors like food, environment, and industry. Enzymes are finding
newer and newer utilities/applications as biotechnology is advancing. Enzymes
derived from filamentous fungi are commercially sound over the bacteria or yeast
in terms of not only quality but quantity too (Bakri et al. 2003). Cellulase is
efficiently synthesized by Aspergillus niger as well as Tricoderma viride, which
are considered as safe organisms (Comacho and Aguilar 2003). These organisms are
being used from a long time for production of extracellular enzymes, as these
organisms possess potent protein secretion machinery that generates homologous
and heterologous proteins. A. niger is a known organism to generate huge variety of
enzymes, specially xylanases, hemicellulases, cellulases, and pectinases. With the
aid of these enzymes, A. niger has potential to degrade plant cell material in its
natural environment (de Vries 2003). Cost-effective sugars that are produced
through enzymatic saccharification of cellulose can be fermented into biofuels and
biochemicals (Kotchoniet al. 2003). Natural cellulose is made up of straight
homopolysaccharide, where D-glucose residues connected with β-1,4-glucosidic
bonds to that give rise to a polymeric chain. Cellobiose consists of two glucose
units and is considered as smallest repetitive unit in cellulose. Cellobiose and
glucose sugars are generated from cellulose when its β-bonds are hydrolyzed,
thereby making cellulose as a valuable substrate for fabrication of value-added
chemicals/products including biofuels (Chandel et al. 2012b). There are many
microorganisms that produce cellulolytic enzymes. Prominent among them are
bacteria and fungi that can degrade cellulose with the aid of their cellulolytic
enzymes. These extracellular cellulases have extensive potential to solubilize crystalline cellulose (Mach and Zeilinger2003). The fungi with the same potential belong
either to the white rot basidiomycetes, deuteromycetes, or ascomycetes group.
Thermophiles along with other wide variety of mesophiles, anaerobes, aerobes,
bacteria, fungi, and actinomycetes are capable of producing cellulases (Rao et al.
2013). A complete complex of cellulases and that too of high yield is produced by
fungi, which make them most studied organisms. T. reesei, T. viride, P. pinophinum,
P. chrysosporium, F. solani, T. emersonii, T. koningii, and R. oryzae are aerobic
fungi that are well characterized for their capacity to produce celluloses (Bhat and
Bhat 1997; Murashimaet al. 2002). Interestingly, C. thermophile, H. insolens, H.
grisea, T. moidea, M. thermophila, T. emersonii, and T. aurantiacus (Maheswariet
al. 2002) are the prominent aerobic thermophilic fungi capable of producing
cellulases. While, N. frantalis, P. communis, and S. communis are the prominent
mesophilic fungi that also have potential to produce cellulases (Bhat and Bhat 1997).
Microorganism secretes the cellulolytic enzymes into the medium. These enzymes
are also associated with the outer surface of microorganisms that is capable of
degrading cellulose. The enzymology of cellulose degradation is documented in
several reviews (Kang et al. 1999; Lynd et al. 2003). Four types of enzymes are
found to involve in the saccharification process of cellulosic biomass: (1)
Endoglucanases (endo-1,4-β-D-glucan-4-glucanohydrolase, EC 3.2.1.4) randomly
3 Role of Thermophiles in Production of Aviation Biofuels: Fueling the Future
69
Microbial Enzymology of Biofuel Production Including
Thermophiles
Enzyme constitutes one of the vital bioproducts and finds its utility in many
technological sectors like food, environment, and industry. Enzymes are finding
newer and newer utilities/applications as biotechnology is advancing. Enzymes
derived from filamentous fungi are commercially sound over the bacteria or yeast
in terms of not only quality but quantity too (Bakri et al. 2003). Cellulase is
efficiently synthesized by Aspergillus niger as well as Tricoderma viride, which
are considered as safe organisms (Comacho and Aguilar 2003). These organisms are
being used from a long time for production of extracellular enzymes, as these
organisms possess potent protein secretion machinery that generates homologous
and heterologous proteins. A. niger is a known organism to generate huge variety of
enzymes, specially xylanases, hemicellulases, cellulases, and pectinases. With the
aid of these enzymes, A. niger has potential to degrade plant cell material in its
natural environment (de Vries 2003). Cost-effective sugars that are produced
through enzymatic saccharification of cellulose can be fermented into biofuels and
biochemicals (Kotchoniet al. 2003). Natural cellulose is made up of straight
homopolysaccharide, where D-glucose residues connected with β-1,4-glucosidic
bonds to that give rise to a polymeric chain. Cellobiose consists of two glucose
units and is considered as smallest repetitive unit in cellulose. Cellobiose and
glucose sugars are generated from cellulose when its β-bonds are hydrolyzed,
thereby making cellulose as a valuable substrate for fabrication of value-added
chemicals/products including biofuels (Chandel et al. 2012b). There are many
microorganisms that produce cellulolytic enzymes. Prominent among them are
bacteria and fungi that can degrade cellulose with the aid of their cellulolytic
enzymes. These extracellular cellulases have extensive potential to solubilize crystalline cellulose (Mach and Zeilinger2003). The fungi with the same potential belong
either to the white rot basidiomycetes, deuteromycetes, or ascomycetes group.
Thermophiles along with other wide variety of mesophiles, anaerobes, aerobes,
bacteria, fungi, and actinomycetes are capable of producing cellulases (Rao et al.
2013). A complete complex of cellulases and that too of high yield is produced by
fungi, which make them most studied organisms. T. reesei, T. viride, P. pinophinum,
P. chrysosporium, F. solani, T. emersonii, T. koningii, and R. oryzae are aerobic
fungi that are well characterized for their capacity to produce celluloses (Bhat and
Bhat 1997; Murashimaet al. 2002). Interestingly, C. thermophile, H. insolens, H.
grisea, T. moidea, M. thermophila, T. emersonii, and T. aurantiacus (Maheswariet
al. 2002) are the prominent aerobic thermophilic fungi capable of producing
cellulases. While, N. frantalis, P. communis, and S. communis are the prominent
mesophilic fungi that also have potential to produce cellulases (Bhat and Bhat 1997).
Microorganism secretes the cellulolytic enzymes into the medium. These enzymes
are also associated with the outer surface of microorganisms that is capable of
degrading cellulose. The enzymology of cellulose degradation is documented in
several reviews (Kang et al. 1999; Lynd et al. 2003). Four types of enzymes are
found to involve in the saccharification process of cellulosic biomass: (1)
Endoglucanases (endo-1,4-β-D-glucan-4-glucanohydrolase, EC 3.2.1.4) randomly
3 Role of Thermophiles in Production of Aviation Biofuels: Fueling the Future
69