Abstract
Many traditional mutagenic strategies have been used to improve cellulase production by micro-organisms, especially fungi species. Trichoderma species are among cellulolytic fungi, those that have been most extensively studied, due to their efficient production of these enzymes. In the present study, N-methyl-N´-nitro-N-nitrosoguanidine (NTG) was used as mutagenic agent to obtain cellulolytic mutant from wild strain T. atroviride 676. After mutagenic procedures, two strains (102C1 and 104C2) were selected as promising cellulase-producing mutant. The effect of the carbon (sugarcane bagasse: SCB) and nitrogen (corn steep liquor: CSL) sources on endoglucanase production by the mutants 102C1 and 104C2 was studied using submerged cultivations at 28°C. Different concentrations of SCB and CSL were used and nine different media were generated. Mutant 102C1 showed the best results when using 2.5% SCB and 0.7% CSL. A central composite rotational design (CCRD) was performed to estimate optimal conditions of pH and temperature for endoglucanase activity of strain 102C1, which were pH 3.6 and temperature 66°C. The characterization of this acidophilic and thermophilic endoglucanase activity produced by the mutant strain 102C1 allows its use in biotechnological applications, particularly in the hydrolysis of agro industrial residues, such as SCB, for bioethanol production. Key words: Trichoderma atroviride, CMCase, nitrosoguanidine, sugarcane bagasse, corn steep liquor.
Highlights
Cellulose, a glucose polymer linked by β-1,4 bonds, is considered to be the primary product of photosynthesis and carbon renewable resources that is highly abundant in nature (Gottschalk et al, 2010; Deswal et al, 2014)
The T. atroviride 676 wild strain was previously identified as promising producer of enzymes of the lignocellulolytic complex (Grigorevski-Lima et al, 2013)
Strain 676 and strain NTG21 were used, and 27 strains were obtained, 24 from strain NTG21 and 3 from strain 676. When these strains were tested for cellulase production in CMCCongo red and cellulose-azure media, they were all positive
Summary
A glucose polymer linked by β-1,4 bonds, is considered to be the primary product of photosynthesis and carbon renewable resources that is highly abundant in nature (Gottschalk et al, 2010; Deswal et al, 2014). Lignocellulosic material can be used to produce ethanol after cellulose hydrolysis with cellulases. Cost of cellulase is still the major obstacle associated to hydrolysis of cellulosic materials into fermentable sugars. Improvements towards a cost effective cellulase production is essential to make this process economically viable (Adsul et al, 2007; Soccol et al, 2010; Borges et al, 2014). The cellulase complex secreted by filamentous fungi consists of three main components, endo-1,4-β-glucanase (EC 3.2.1.4), β-1,4glucan cellobiohydrolase (EC 3.2.1.91), and βglucosidase (EC 3.2.1.21). These three enzymes act in synergy during the conversion of cellulose to glucose (Wilson, 2011)
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