Enhancement of Isobutanol and 3-Methyl-1-Butanol Production Yields in Saccharomyces Cerevisiae without Genetic Modification

Abstract

Bio-based fuel produced from the renewable resources is efficiently overcome the shortcomings of fossil fuels. Several factors such as the increasing awareness on environmental problems, fossil fuel prices  and the sustainability of energy has encouraged the initiative in finding another source of transportation fuels. Higher alcohols have proved to be a better candidate to replace gasoline as vehicle fuel due to characteristics of higher energy content, low solubility in water, lower vapor pressure and higher blending ability with gasoline. Biologically, isobutanol and 3-methyl-1-butanol are produced through the fermentation of renewable feedstock with microorganism. Saccharomyces cerevisiae is known to be able to produce isobutanol and 3-methyl-1-butanol titers naturally without heterologous pathways. However, the production of these alcohols by Saccharomyces cerevisiae is only in a small quantity, thus several efforts in enhancing the isobutanol and 3-methyl-1-butanol yields have been conducted. In this study, the amino acids (valine and leucine) and amino acid precursor (2-ketoisovalerate) were added into the fermentation medium prior to the fermentation. The results obtained show that the supplementation of 2-ketoisovalerate and leucine individually into the fermentation broth leads to the increased in isobutanol and 3-methyl-1-butanol titers by 3.3 folds and 1.9 folds, respectively. The combination of 2-ketoisovalerate and valine increased the isobutanol yield by 4.3 folds while the 3-methyl-1-butanol was increased by 2.5 folds when supplemented with 2-ketoisovalerate and leucine. These results portray that the isobutanol and 3-methyl-1-butanol titers can be improved by manipulating several factors which is important for future production of higher alcohols.