A Mutated Yeast Strain with Enhanced Ethanol Production Efficiency and Stress Tolerance

One of the strategies to improve and optimize bio-ethanolproduction from new feed stocks is to develop new strainsof Saccharomyces cerevisiae with tolerance to stresses. Themain objectives here were to; generate S. cerevisiae mutantstolerant to high ethanol concentrations; test for their abilityto ferment maize starch; and partially characterize the mutationsresponsible for the new phenotypes. A combinationof mutagenesis, selection and cross-stress protection methodswere used. EMS (ethyl methanesulfonate) was used tomutagenize one S. cerevisiae strain. The mutagenized yeaststrain was exposed to high concentrations of ethanol andtolerant mutants were isolated. Mutants showed improvedethanol yield (0.02-0.03 g/g of maize) and fermentation efficiency(3-5%). Finally, AFLP (Amplified Fragment LengthPolymorphism) was performed to identify polymorphisms inthe mutants that might underlie the strains ethanol tolerance.The best performing mutant isolate had four altered genetranscripts encoding; an arginine uptake and canavanine resistanceprotein (CAN1); mitochondrial membrane proteins(SLS1); a putative membrane glycoprotein (VTH1); and cytochromeC oxidase (COX6; EC 1.9.3.1) among about 1,000tested. It was concluded these mutations might underlie theimproved ethanol production efficiency and stress tolerance.