Evolutionary engineering improves tolerance for medium-chain alcohols in Saccharomyces cerevisiae

Abstract

Yeast-based chemical production is an environmentally friendly alternative to petroleum-based production or processes that involve harsh chemicals. However, many potential alcohol biofuels, such as n -butanol, isobutanol and n -hexanol, are toxic to production organisms, lowering the efficiency and cost-effectiveness of these processes. We set out to improve the tolerance of Saccharomyces cerevisiae toward these alcohols. We evolved the laboratory strain of S. cerevisiae BY4741 to be more tolerant toward n -hexanol and show that the mutations which confer tolerance occur in proteins of the translation initiation complex. We found that n -hexanol inhibits initiation of translation and evolved mutations in the α subunit of eIF2 and the γ subunit of its guanine exchange factor eIF2B rescue this inhibition. We further demonstrate that translation initiation is affected by other alcohols such as n -pentanol and n -heptanol, and that mutations in the eIF2 and eIF2B complexes greatly improve tolerance to these medium-chain alcohols. We successfully generated S. cerevisiae strains that have improved tolerance toward medium-chain alcohols and have demonstrated that the causative mutations overcome inhibition of translation initiation by these alcohols.