Development of Thermotolerant Yeast for Simultaneous Saccharification and Co-Fermentation of Polysaccharides Present in Lignocelluloses for the Production of Bioethanol

Second generation bioethanol has already been proved as a great alternative to the gasoline, and recommended to be blended with gasoline in transportation vehicles. In a particular, for the sustainable bioethanol production, xylose, the second highest monosaccharide in lignocellulosic residues, has to be converted in ethanol simultaneously with the glucose. Various xylose utilizing yeasts such as Scheffersomyces stipitis, Candida shehatae, Candida intermedia and Kluyveromyces marxianus have been reported for xylose-based ethanol production. However, various issues like slow xylose uptake, higher byproduct formation, low ethanol productivity, have been encountered during the process development. In this regard, targeted and non-targeted engineering have been approached by different researches to overcome the issues. The targeted engineering has been applied the different levels such as xylose metabolic and transporter engineering, co-factor regeneration, establishment of bypass pathway etc. The genetic engineering tools, applied for the improvement include gene insertion from one organism to potential xylose utilizing strain for xylose metabolism and uptake, site directed mutagenesis for glucose/xylose diauxic during sugar transport, to change the co-factor preference of xylose metabolic enzymes and inhibition of parallel pathway of other product formation.