Thermostable Recombinant Cellulases of the Thermophilic Mold Myceliophthora thermophila in the Bioconversion of Paddy Straw and Sugarcane Bagasse to Ethanol

Lignocellulosic cellulose serves as a key source for bioethanol production. The efficient conversion of cellulose relies on three major cellulase components. High cost of cellulases and the need for a single microbe that produces all cellulase components in the right proportion and quantities are a few challenges in bioethanol production from cellulose. This investigation is an attempt in developing an enzyme cocktail involving recombinant thermostable cellulases (rMtEgl, rMtCel6A and rMtBgl3c) of the thermophilic mold Myceliophthora thermophila and testing their applicability in the conversion of agro residues to ethanol for the first time. The most effective pretreatment method for paddy straw and sugarcane bagasse was optimized. Pretreatment of sugarcane bagasse with sodium chlorite and acetic acid resulted in a 5.5-fold increase in total reducing sugar liberation, while, in paddy straw, total reducing sugar release increased by 9-fold, when biomass was treated with NaOH and microwaves compared to untreated biomass. The inclusion of recombinant enzymes in the enzyme cocktail supported 80-90% saccharification of pretreated paddy straw and sugarcane bagasse, which is 2-fold higher than that achieved using commercial enzyme mix alone. The ethanol production levels of 55.8 and 37.0 g/L, with the fermentation efficiencies of 80 and 76%, were attained from the pre-treated paddy straw and sugarcane bagasse hydrolysates, respectively. An appropriate blend of each enzyme component and pretreatment method tailored for the specific biomass is crucial for efficient biofuel production.

Automated summary

This study attempts to develop an enzyme cocktail for the conversion of agricultural residues to ethanol. By utilizing recombinant enzymes and optimizing pretreatment methods, high saccharification rate and ethanol production levels were achieved.