Geopolitical concerns (unstable supply of gasoline, environmental pollution, and regular price hikes), economic, and employment concerns have been prompting researchers, entrepreneurs, and policy makers to focus on harnessing the potential of lignocellulosic feedstock for fuel ethanol production and its commercialization. The carbohydrate skeleton of plant cell walls needs to be depolymerised into simpler sugars for their application in fermentation reactions as a chief carbon source of suitable ethnologic strains for ethanol production. The role of cellulolytic enzymes in the degradation of structural carbohydrates of the plant cell wall into ready-to-fermentable sugar stream is inevitable. Cellulase synergistically acts upon plant cell wall polysaccharides to release glucose into the liquid media. Cellulase predominantly dominates all the plant cell wall degrading enzymes due to their vast and diverse range of applications. Apart from the major applications of cellulases such as in detergent formulations, textile desizing, and development of monogastric feed for ruminants, their role in biorefinery is truly remarkable. This is a major area where new research tools based upon fermentation based formulations, biochemistry, and system biology to expedite the structure-function relationships of cellulases including cellulosomes and new designer enzymatic cocktails are required. In the last two decades, a considerable amount of research work has been performed on cellulases and their application in biomass saccharification. However, there are still technical and economic impediments to the development of an inexpensive commercial cellulase production process. Advancements in biotechnology such as screening of microorganisms, manipulation of novel cellulase encoding traits, site-specific mutagenesis, and modifications to the fermentation process could enhance the production of cellulases. Commercially, cheaper sources of carbohydrates and modified fermentation conditions could lead to more cost-effective production of cellulases with the goal to reduce the cost of ethanol production from lignocellulosics. Implementation of integrated steps like cellulase production and cellulase mediated saccharification of biomass in conjunction with the fermentation of released sugars in ethanol in a single step so called consolidated bio-processing (CBP) is very important to reduce the cost of bioethanol. This paper aims to explore and review the important findings in cellulase biotechnology and the forward path for new cutting edge opportunities in the success of biorefineries.

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The imposition of ethanol derived from biomass for blending in gasoline would make countries less dependent on current petroleum sources, which would save foreign exchange reserves, improve rural economies and provide job opportunities in a clean and safe environment. The key drivers for successful commercial ethanol production are cheap raw materials, economic pretreatment technologies, in-house cellulase production with high and efficient titers, high ethanol fermentation rates, downstream recovery of ethanol and maximum by-products utilization. Furthermore, recent developments in engineering of biomass for increased biomass, down-regulation of lignin synthesis, improved cellulase titers and re-engineering of cellulases, and process integration of the steps involved have increased the possibility of cheap bioethanol production that competes with the price of petroleum. Recently, many companies have come forward globally for bioethanol production on a large scale. It is very clear now that bioethanol will be available at the price of fossil fuels by 2010. This article intends to provide insight and perspectives on the important recent developments in bioethanol research, the commercialization status of bioethanol production, the step-wise cost incurred in the process involved, and the possible innovations that can be utilized to reduce the cost of ethanol production.

Ethanol has drawn attention worldwide to be a true alternative of fossil fuel due to its renewable nature and economics. In the present study, we aimed to evaluate a cheaper and abundantly available wild species of sugarcane, Saccharum spontaneum, as the raw substrate for ethanol production under simultaneous saccharification and fermentation (SSF) conditions. The substrate was first pretreated with aqueous ammonia followed by enzymatic hydrolysis coupled with the fermentation of released sugars into ethanol by monoculture as well as mixed cultures of thermotolerant S. cerevisiae VS 3 and P. stipitis NCIM 3498. The cellulase enzyme used for saccharification was prepared from the culture supernatants of Aspergillus oryzae MTCC1846 grown under submerged fermentation conditions. A maximum of 0.85 ± 0.07 IU/mL of filter paperase (FPase), 1.25 ± 0.04 IU/mL of carboxy methyl cellulase (CMCase) and 55.56 ± 0.52 IU/mL of xylanase activity was obtained after 7 days of incubation using delignified S. spontaneum as carbon source under submerged fermentation conditions. During SSF, P. stipitis, VS 3 and mixed culture showed ethanol production-15.73±0.44 g/l (productivity, 0.218±0.04 g/l/h), 14.22±0.15 g/l (productivity, 0.197±0.02 g/l/h) and 17.73 ± 0.25 g/l (productivity, 0.246 ± 0.02 g/l/h), respectively.

Groundnut shell (GS), after separation of pod, is readily available as a potential feedstock for production of fermentable sugars. The substrate was delignified with sodium sulfite. The delignified substrate released 670 mg/g of sugars after enzymatic hydrolysis (50• C, 120 rpm, 50 hrs) using commercial cellulases (Dyadic Xylanase PLUS, Dyadic Inc. USA). The groundnut shell enzymatic hydrolysate (45.6 g/L reducing sugars) was fermented for ethanol production with free and sorghum stalks immobilized cells of Pichia stipitis NCIM 3498 under submerged cultivation conditions. Immobilization of yeast cells on sorghum stalks were confirmed by scanning electron microscopy (SEM). A maximum of ethanol production (17.83 g/L, yield 0.44 g/g and 20.45 g/L, yield 0.47 g/g) was observed with free and immobilized cells of P. stipitis respectively in batch fermentation conditions. Recycling of immobilized cells showed a stable ethanol production (20.45 g/L, yield 0.47 g/g) up to 5 batches followed by a gradual downfall in subsequent cycles.

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