ABSTRACT
Ethanol is an ideal fuel and the basis for countless chemical transformations. Worldwide interest in the production of ethanol as a source of renewable energy oscillated throughout the twentieth century, due to low oil prices. In recent years, the use of ethanol has increased dramatically. Ethanol attracted more attention due to its application as an octane enhancer and as a substitute for petrol. A significant number of automobiles in countries with vast supplies of fermentable sugar, such as Brazil, are nowadays fueled by ethanol or ethanol-petroleum mixtures (Ingledew 1993; Walker 1998). Continued increase of ethanol production will depend on process improvements, and reduction in fermentative ethanol costs. In those carbohydrate-to-ethanol processes where microorganisms are involved, optimal conversion requires cells that are tolerant to high concentrations of both substrate and product and are able to efficiently produce ethanol (Walker 1998). Saccharomyces yeasts are the most ethanoltolerant of eucaryotic organisms, able to produce over 20% ethanol (Casey and Ingledew 1986). However, there are different ways of improving ethanol production: increasing the range of substrates used as feedstock, improving the efficiency of substrate conversion to ethanol, raising the fermentation temperature, or improving tolerances to ethanol and osmotic pressure. For these reasons attention has been given to yeasts other than Saccharomyces capable of fermenting substrates not accessible to the former such as inulin, starch, lactose, cellobiose, cellulose, hemicellulose, or xylose (Ingledew 1993; Walker 1998).
