The yield of isobutanol was improved from 0.16 to 0.97 mg per g glucose by simultaneous overexpression of biosynthetic genes ILV2, ILV3, and ILV5 in valine metabolism in anaerobic fermentation of glucose in mineral medium in S. cerevisiae. Isobutanol yield was further improved by two times by the additional overexpression of BAT2, encoding the cytoplasmic branched-chain amino acid aminotransferase.

Overexpression of genes ILV2, ILV3, ILV5, and BAT2 in valine metabolism led to an increase in isobutanol production in S. cerevisiae. Additional overexpression of ILV6 in the ILV2 ILV3 ILV5 overexpression strain had a negative effect, presumably by increasing the sensitivity of Ilv2 to valine inhibition, thus weakening the positive impact of overexpression of ILV2, ILV3, and ILV5 on isobutanol production. Aerobic cultivations of the ILV2 ILV3 ILV5 overexpression strain and the reference strain showed that supplying amino acids in cultivation media gave a substantial improvement in isobutanol production for the reference strain, but not for the ILV2 ILV3 ILV5 overexpression strain.

—Chen et al.

Resources

• Xiao Chen, Kristian F Nielsen, Irina Borodina, Morten C Kielland-Brandt and Kaisa Karhumaa (2011) Increased isobutanol production in Saccharomyces cerevisiae by overexpression of genes in valine metabolism. Biotechnology for Biofuels 4:21 doi: 10.1186/1754-6834-4-21