**6. Characterization of cellulase**

*Elements of Bioeconomy*

Carbon sources (5% w/v in SmF and 4% w/w in SSF)

fit because of their higher cost.

**5. Purification of cellulase**

, Cu2+, Hg2+, Fe3+, K+

*Effect of supplementation of various carbon sources [106].*

inhibitory of cellulase, whereas metal ions such as Ca2+, Co2+ and Na+

ions such as Ag+

**Table 3.**

wastes millet, guinea corn straw, rice husks and maize straw as carbon sources for cellulase production by *Aspergillus niger*. According to Mrudula and Murugammal [85] lactose was found to be the best inducer in SmF and SSF (**Table 3**). Prasanna et al. [110] also reported lactose as the most excellent carbon source for cellulase production by *Penicillium* sp. followed by carboxymethyl cellulose and galactose. Different researchers studied the effect of various nitrogen sources for cellulase production by employing different microbes. Peptone was reported as most effective nitrogen source for Penicillium sp. [110], *Penicillium waksmanii* F10-2 [111], urea for *A. niger* [89] and NH4NO3 for *Trichoderma reesei* NRRL 11460 [112]. Although the addition of beef extract and peptone (as organic nitrogen source) leads to enhanced growth and enzyme production but they were not economically

**Supplement SmF (U/mL) SSF (U/gDMB)**

Control 0.7 0.4 3.7 2 Glucose 1.52 0.54 11.1 6.5 Xylose 1.2 1.42 15.7 6.6 Lactose 3 1.71 18 10.9 Maltose 1.51 1.5 17.5 6.3 Sucrose 1.54 1.51 13.7 6.2

**CMCase FPase CMCase FPase**

Cellulase production by some microorganisms has been found to be influenced by metal ions, chelators, detergents and surfactants. It was reported that usually metal

or does not affect the cellulase activity [113]. Addition of Tween20 leads to a significant increase in endoglucanase and xylanase production by *Melanocarpus* sp. MTCC 3922 [114]. Cellulase activity increased with Tween80 and reduced with SDS [115]. Enhancement in enzyme production by Tween80 may be due to increase in permeability of cell membrane allowing rapid secretion and synthesis of the enzymes [116].

It is an important step to remove any contaminants that are found to be present in the mixture. Hence, it is a vital step required for improving performance/ functioning of an enzyme. Enzymes in the culture supernatant could be purified by the conventional methods which include ammonium sulfate precipitation and dialysis followed by column chromatography [117]. The most common matrix for gel exclusion chromatography is the Sephadex with different pore sizes which is employed in the purification of cellulase [118]. The purification folds and % yield are the two most important factors which are used to evaluate the efficiency of purification. First step (ammonium salt precipitation) is based upon difference in protein solubility. The solubility of protein firstly increase and then starts decreasing with increase in salt concentration and finally protein gets precipitate. This

, Mn2+, Mg2+, and Zn2+ are slightly or completely

either stimulate

**70**

Different researchers reported different temperatures for maximum cellulase production. It is reported that the optimal temperature for cellulase production varies from strain to strain of microorganisms [69]. The optimum temperature of fungal cellulases ranges from 40 to 60°C and pH found to be 4.8. A battery of thermophilic fungal strains are known to produce thermostable enzymes which are stable and active at such high temperature which are not optimum for the growth of the microorganism. Filamentous fungi, e.g., *Talaromyces emersonii*, *Thermoascus aurantiacus* and *Chaetomium thermophilum* are reported to produce cellulases having high-cellulase activity at elevated temperature [124]. The Km value is used for the measurement of enzyme affinity towards the substrate. An increase in substrate concentration made more binding sites available for the enzymes to adhere and the rate at which product formation would be achieved therefore would be faster [125]. In literature, different ranges of Km and Vmax for different fungal species have been reported. Genetic variability may be a factor for the above reported variation [126]. Taha et al. [127] reported cellulase showing optimum activity at pH 6 and 50°C with (Vmax) of 75 g l<sup>−</sup><sup>1</sup> min<sup>−</sup><sup>1</sup> mg<sup>−</sup><sup>1</sup> with its corresponding Km value of 2.5 × 10<sup>−</sup><sup>5</sup> g/l.
