Abstract
Scarcity of the non-renewable energy sources, global warming, environmental pollution, and raising the cost of petroleum are the motive for the development of renewable, eco-friendly fuels production with low costs. Bioethanol production is one of the promising materials that can subrogate the petroleum oil, and it is considered recently as a clean liquid fuel or a neutral carbon. Diverse microorganisms such as yeasts and bacteria are able to produce bioethanol on a large scale, which can satisfy our daily needs with cheap and applicable methods. Saccharomyces cerevisiae and Pichia stipitis are two of the pioneer yeasts in ethanol production due to their abilities to produce a high amount of ethanol. The recent focus is directed towards lignocellulosic biomass that contains 30–50% cellulose and 20–40% hemicellulose, and can be transformed into glucose and fundamentally xylose after enzymatic hydrolysis. For this purpose, a number of various approaches have been used to engineer different pathways for improving the bioethanol production with simultaneous fermentation of pentose and hexoses sugars in the yeasts. These approaches include metabolic and flux analysis, modeling and expression analysis, followed by targeted deletions or the overexpression of key genes. In this review, we highlight and discuss the current status of yeasts genetic engineering for enhancing bioethanol production, and the conditions that influence bioethanol production.
Highlights
The excessive usage of fossil fuels to satisfy the rapid increase of energy demand has created severe environmental problems, such as air pollution, acid rain, and global warming [1]
These results proposed that engineered S. cerevisiae originally utilizes the high-affinity system for xylose transport
This result demonstrated the importance of XK activity and reflected one of the highest ethanol yield obtained by genetically engineered S. cerevisiae with reasonable fast rate of xylose/glucose fermentation [80]
Summary
The excessive usage of fossil fuels to satisfy the rapid increase of energy demand has created severe environmental problems, such as air pollution, acid rain, and global warming [1]. The utilization of multiple sugars of arabinose, rhamnose, xylose, galactose, mannose, and glucose in the presence of ferulic and acetic acids, along with diverse disintegration products from thermal and chemical pretreatment, is the limiting factor of the fermentation process. The pentose sugar xylose from plant hydrolysates cannot be fermented by Saccharomyces cerevisiae (wild types strains), which is the communally used for ethanol production. The bio-renewable chemicals and fuels fermentative production need the biocatalysts engineering that can quickly and efficiently transform sugars to the target products with lower cost than the existing petrochemical-based processes. The technical and economical biotransformation of pentoses sugars to ethanol are still challenging [12,76,77,78,79], many achievements in genetic engineering have been done to ferment arabinose and xylose to lactic acid and ethanol. The interconversion of pentoses and pentitols by NAD (PH)-mediated oxidoreductases [11,80]
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