(Lynd et al. 2002; Zhang and Zhang 2013). Some microorganisms producing
β-Glucosidase can be seen in Fig. 9.5 (Yeoman et al. 2010; Sakamoto et al. 2012;
López-Mondéjar et al. 2019).
Besides these three mentioned enzymes, there are also non-hydrolytic proteins
(non-acting on ß-1,4 glycosidic linkages) called swollenin which contribute to the
degradation of cellulose. These proteins contribute to the accessibility of the cellulases to cellulose chains, by loosening the cellulolytic fibril networks (Saloheimo
et al. 2002; Binod et al. 2011; Sindhu et al. 2016).
Microorganisms have developed various adaptations for the complete hydrolysis
of the cellulose. Cellulolytic filamentous fungi and actinomycetes are able to diffuse
into cellulolytic substrates along with the fiber extensions, and the enzymes in these
systems do not constitute great stable complexes with respect to molecular weight.
Therefore, they are called non-complex systems (Lynd et al. 2002). Despite this, the
anaerobic bacteria do not have the ability to effectively diffuse into the cellulosic
material. For this reason, since the ATP is limited, other microorganisms have had to
develop an alternative mechanism called cellulosome for synthesizing cellulase
(Schwarz 2001; Doi and Kosugi 2004).
9.3.2 Complex Cellulose Systems (Cellulosome)
Cellulosome is a multienzymatic extracellular enzyme complex that exists in anaerobic bacteria and can degrade cellulose, hemicellulose, and pectin (Schwarz 2001;
Duan et al. 2009; Carrillo-Reyes et al. 2016). Cellulosome is also described as the
cellulose-binding factor which binds the anaerobic bacteria cells to cellulose particles and minimizes the diffusion loss of the hydrolytic products (Stern et al. 2015).
Typical ruminal bacteria types such as Ruminococcus, Butyrivibrio, and Clostridium
are examples that form cellulosomes (Schwarz 2001; Doi and Kosugi 2004).
The main component of the cellulosome complex is a catalytic or non-catalytic
essential protein called scaffolding (Doi and Kosugi 2004; Brás et al. 2012).
Catalytic scaffold contains the multiple dockerin protein which has degradative
enzymes. Non-catalytic scaffold contains numerous copies of the cohesin modules
and carbohydrate-binding modules (CBM). This CBM is responsible for connecting
cellulase on the cellulosic substrate (Dassa et al. 2017; Haitjema et al. 2017).
The non-covalent interaction between cohesin-dockerin plays roles in arranging
the assembly of cellulosomes and helping the scaffolding to bind the enzyme subunits into the complex (Bégum and Lemaire 1996; Mechaly et al. 2001; Prasad et al.
2019).
The primary examples of the enzymes that are included in the cellulosome
complex are cellulases (endoglucanases, exoglucanases, cellobiohydrolases),
xylanases, mannanases, and pectate lyases. The presence of these enzymes shows
that the cellulosomes can break down all the cell wall compounds (Haitjema et al.
2017).
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269
β-Glucosidase can be seen in Fig. 9.5 (Yeoman et al. 2010; Sakamoto et al. 2012;
López-Mondéjar et al. 2019).
Besides these three mentioned enzymes, there are also non-hydrolytic proteins
(non-acting on ß-1,4 glycosidic linkages) called swollenin which contribute to the
degradation of cellulose. These proteins contribute to the accessibility of the cellulases to cellulose chains, by loosening the cellulolytic fibril networks (Saloheimo
et al. 2002; Binod et al. 2011; Sindhu et al. 2016).
Microorganisms have developed various adaptations for the complete hydrolysis
of the cellulose. Cellulolytic filamentous fungi and actinomycetes are able to diffuse
into cellulolytic substrates along with the fiber extensions, and the enzymes in these
systems do not constitute great stable complexes with respect to molecular weight.
Therefore, they are called non-complex systems (Lynd et al. 2002). Despite this, the
anaerobic bacteria do not have the ability to effectively diffuse into the cellulosic
material. For this reason, since the ATP is limited, other microorganisms have had to
develop an alternative mechanism called cellulosome for synthesizing cellulase
(Schwarz 2001; Doi and Kosugi 2004).
9.3.2 Complex Cellulose Systems (Cellulosome)
Cellulosome is a multienzymatic extracellular enzyme complex that exists in anaerobic bacteria and can degrade cellulose, hemicellulose, and pectin (Schwarz 2001;
Duan et al. 2009; Carrillo-Reyes et al. 2016). Cellulosome is also described as the
cellulose-binding factor which binds the anaerobic bacteria cells to cellulose particles and minimizes the diffusion loss of the hydrolytic products (Stern et al. 2015).
Typical ruminal bacteria types such as Ruminococcus, Butyrivibrio, and Clostridium
are examples that form cellulosomes (Schwarz 2001; Doi and Kosugi 2004).
The main component of the cellulosome complex is a catalytic or non-catalytic
essential protein called scaffolding (Doi and Kosugi 2004; Brás et al. 2012).
Catalytic scaffold contains the multiple dockerin protein which has degradative
enzymes. Non-catalytic scaffold contains numerous copies of the cohesin modules
and carbohydrate-binding modules (CBM). This CBM is responsible for connecting
cellulase on the cellulosic substrate (Dassa et al. 2017; Haitjema et al. 2017).
The non-covalent interaction between cohesin-dockerin plays roles in arranging
the assembly of cellulosomes and helping the scaffolding to bind the enzyme subunits into the complex (Bégum and Lemaire 1996; Mechaly et al. 2001; Prasad et al.
2019).
The primary examples of the enzymes that are included in the cellulosome
complex are cellulases (endoglucanases, exoglucanases, cellobiohydrolases),
xylanases, mannanases, and pectate lyases. The presence of these enzymes shows
that the cellulosomes can break down all the cell wall compounds (Haitjema et al.
2017).
9 Microbial and Bioinformatics Approach in Biofuel Production
269