Lignocellulosic Fermentation of Wild Grass Employing Recombinant Hydrolytic Enzymes and Fermentative Microbes with Effective Bioethanol Recovery

Saprativ P Das,Debasish Das,Ashutosh Gupta,Arabinda Ghosh,Arun Goyal

doi:10.1155/2013/386063

Saprativ P Das, Debasish Das + Show 3 more

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https://doi.org/10.1155/2013/386063

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Abstract

Simultaneous saccharification and fermentation (SSF) studies of steam exploded and alkali pretreated different leafy biomass were accomplished by recombinant Clostridium thermocellum hydrolytic enzymes and fermentative microbes for bioethanol production. The recombinant C. thermocellum GH5 cellulase and GH43 hemicellulase genes expressed in Escherichia coli cells were grown in repetitive batch mode, with the aim of enhancing the cell biomass production and enzyme activity. In batch mode, the cell biomass (A 600 nm) of E. coli cells and enzyme activities of GH5 cellulase and GH43 hemicellulase were 1.4 and 1.6 with 2.8 and 2.2 U·mg−1, which were augmented to 2.8 and 2.9 with 5.6 and 3.8 U·mg−1 in repetitive batch mode, respectively. Steam exploded wild grass (Achnatherum hymenoides) provided the best ethanol titres as compared to other biomasses. Mixed enzyme (GH5 cellulase, GH43 hemicellulase) mixed culture (Saccharomyces cerevisiae, Candida shehatae) system gave 2-fold higher ethanol titre than single enzyme (GH5 cellulase) single culture (Saccharomyces cerevisiae) system employing 1% (w/v) pretreated substrate. 5% (w/v) substrate gave 11.2 g·L−1 of ethanol at shake flask level which on scaling up to 2 L bioreactor resulted in 23 g·L−1 ethanol. 91.6% (v/v) ethanol was recovered by rotary evaporator with 21.2% purification efficiency.

Highlights

Rapid diminution in the accessibility of fossil fuels poses a serious need for sustainable development of alternative energy source
An efficient pretreatment method for the lignin content removal with accessibility to hydrolytic enzymes becomes essential to enrich the availability of utilizable forms of reducing sugars from substrates
Efficacy of implementing recombinant cellulase (GH5) and hemicellulase (GH43) from C. thermocellum expressed in different E. coli BL21 strains was analyzed for hexoses and pentoses production, respectively, which was further utilized for ethanol production from several leafy biomasses using a mixed culture of S. cerevisiae and C. shehatae

Summary

Introduction

Rapid diminution in the accessibility of fossil fuels poses a serious need for sustainable development of alternative energy source. Depletion of oil supply reserves as well as rise in the greenhouse gas emission has glimmered renewed interest in fuel production from renewable resources. Ethanol fermentation from lignocellulosic substrates has been gaining significant concern in the scientific community. Ethanol as a fuel has several advantages over fossil fuels such as greater air-fuel ratio, higher energy density, and added specific energy with heat of vapourization [1]. As ethanol has a high octane number than petrol, no preignition occurs on use of fuel ethanol. Broad use of ethanol is being done as an economical fuel additive with gasoline [1]

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