Environmental Engineering Reference
In-Depth Information
C1 Endoglucanase
ENDO-β-glucanase
EXO-β-glucanase (CBH & GGH)
β-glucosidase
FIGure 30.2
Model of synergistic action of cellulase complex enzymes. (
, crystalline cellulose;
, amorphous cellulose;
, reactive areas;
, cellobiose; , glucose; CBH, cellobiohydrolase;
GGH, glucanase glucohydrolase.)
It has been suggested that from a theoretical point of view, 1100 filter paper units (FPU)/L per hour (C
1
activity) are essential for cellulase production to be commercially successful (Bon and Ferrara 2007).
Therefore, efforts are needed to economize cellulase production by media optimization and use of
supplements/additives. In the literature, many agricultural substrates such as straw, bran, bagasse, etc.
have been reported (Deumas et al. 1995; Pei-Jun et al. 2004). In addition, research is being carried
out on isolation of potential cellulase-producing microorganisms from diverse habitats (Ray et al.
2007). The best productivities and titers for enzyme production by fungal systems have generally been
found for fed-batch operations in which the treated biomass is slowly added to the enzyme production
fermentor during the growth of the fungus and the production of cellulase (Watson et al. 1984;
Allen
and Roche 1989). However, experiments with continuous enzyme production have suffered from lower
cellulase productivities (Allen and Roche 1989; Wyman 1994).
In general, cellulase production is not associated with growth and is strongly influenced by the
nature and concentration of the cellulosic substrate, the pH of the medium, and nutrients (Acerbal
et al. 1986; Kanotra and Mathur 1995; Juhasz et al. 2004). It has been found that high activities
are attainable on a crystalline substrate although the growth rates would be slower than with
amorphous cellulose (Mes-Hartee et al. 1988; Srinivasan and Seetalaxman 1988; Kollar 1994). In
the latter case, the rapid breakdown of the substrate may lead to the formation of free sugars, which
may exhibit catabolite repression, leading to poor utilization of the substrate. One of the approaches
has been to slow down the rate of growth on a readily metabolizable substrate like Solka Floc by
