Stronger Membranes Help Yeast Tolerate Bioenergy Production Chemicals
Incorporating sterols in the outer membrane of Yarrowia lipolytica makes it significantly more tolerant of ionic liquids.
Creating biofuels and other products from plant material is a complex process. Breaking down plant cells requires chemicals, among other things. Organic solvents like ionic liquids (ILs) represent one example. Scientists also need microbes such as yeast to convert the resulting plant material into biofuels and biochemicals. However, ILs often keep microbes from growing. Now, scientists have learned how one strain of yeast, Yarrowia lipolytica, strengthens its membranes. With stronger membranes, this yeast can better withstand ILs.
This study produced the most IL-tolerant microorganism reported to date. It also revealed fundamental mechanisms of IL toxicity and resistance. These insights will be critical to developing robust microbes that can directly convert plant biomass treated with ILs into biofuels and biochemicals.
Environmentally friendly organic solvents such as ILs have versatile uses in producing biofuels and bioproducts. These ILs break down plant material and help microbes convert the plant material into useful products. However, ILs can inhibit these microbes. This is true even at extremely low concentrations of ILs (concentrations of 0.5−1.0 percent). The oleaginous yeast, Yarrowia lipolytica, can naturally grow in 10% concentrations of one type of IL, 1-ethyl-3-methylimidazolium acetate. This ability makes this yeast more tolerant than any laboratory-engineered microorganisms or specific varieties of naturally occurring microorganisms. However, scientists do not fully understand the underlying mechanism for how Y. lipolytica tolerates ILs. Through adaptive laboratory evolution, scientists isolated a strain of Y. lipolytica that tolerates several different types of ILs at concentrations as high as 18 percent. The researchers discovered that the underlying mechanism for robust IL tolerance is in how Y. lipolytica restructures and strengthens its cell membranes by incorporating sterols, a type of natural steroids. While ILs do inhibit the production of sterols in wild (or naturally occurring) Y. lipolytica, scientists may be able to increase how the yeast expresses specific relevant genes. This would cause the naturally occurring Y. lipolytica to tolerate the same high levels of IL as the laboratory strain in this study.
University of Tennessee
Walker, C., S. Ryu, and C. Trinh. 2019. “Exceptional solvent tolerance in Yarrowia lipolytica is enhanced by sterols,” Metabolic Engineering 54(C), 83–95. DOI:10.1016/j.ymben.2019.03.003.