Improving ionic liquid tolerance in Saccharomyces cerevisiae through heterologous expression and directed evolution of an ILT1 homolog from Yarrowia lipolytica


Ionic liquids show promise for deconstruction of lignocellulosic biomass prior to fermentation. Yet, imidazolium ionic liquids (IILs) can be toxic to microbes even at concentrations present after recovery. Here, we show that dominant overexpression of an Ilt1p homolog (encoded by YlILT1/YALI0C04884) from the IIL-tolerant yeast Yarrowia lipolytica confers an improvement in 1-ethyl-3-methylimidazolium acetate tolerance in Saccharomyces cerevisiae compared to the endogenous Ilt1p (ScILT1/YDR090C). We subsequently enhance tolerance in S. cerevisiae through directed evolution of YlILT1 using growth-based selection, leading to identification of mutants that grow in up to 3.5% v/v ionic liquid. Lastly, we demonstrate that strains expressing YlILT1 variants demonstrate improved growth rate and ethanol production in the presence of residual IIL. This shows that dominant overexpression of a heterologous protein (wild type or evolved) from an IIL-tolerant yeast can increase tolerance in S. cerevisiae at concentrations relevant to bioethanol production from IIL-treated biomass.

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We would like to thank Lars Lauffer, Maya Venkataraman, and Eden Williams for helpful assistance with general molecular cloning procedures. We would also like to thank the Brennecke group at UT Austin for providing the alternative ionic liquids (i.e., all IILs other than [EMIM]OAc and [EMIM]Cl) used for supplementary S. cerevisiae BY4741 tolerance testing.


This work was funded through the Camille and Henry Dreyfus Foundation to H.S.A. J.M.W. and K.B.R. acknowledge additional support from the National Science Foundation (NSF) Graduate Research Fellowship Program (DGE-1110007).

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Reed, K.B., Wagner, J.M., d’Oelsnitz, S. et al. Improving ionic liquid tolerance in Saccharomyces cerevisiae through heterologous expression and directed evolution of an ILT1 homolog from Yarrowia lipolytica. J Ind Microbiol Biotechnol 46, 1715–1724 (2019).

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  • Ionic liquids
  • Saccharomyces cerevisiae
  • Yarrowia lipolytica
  • Imidazolium ionic liquid tolerance
  • Directed evolution