17-11: Metabolic engineering of Saccharomyces cerevisiae to produce high-yielding, advanced biofuels strains capable of utilizing C5 and C6 cellulosic sugars

We have engineered S. cerevisiae for robust production of various terpenes by overexpression of the genes that encode the native mevalonate pathway enzymes together with a heterologous terpene synthase.  We achieved production of the terpene, farnesene, by overexpressing the A. annua farnesene synthase.  Initial farnesene-producing strains were improved using a combination of automated, rational strain engineering and repeated mutagenesis and screening.  Our automated strain engineering process is now capable of creating and screening 2000 strains per month.  Currently, our strains produce farnesene using C6 sugars, but in this work our goal was to create yeasts that are capable of utilizing ligno-cellulosic feedstocks.  To achieve this goal, we took an existing C5-utilizing yeast strain and engineered a high-yielding farnesene pathway to create a strain that can produce our product using both C6 and C5 (xylose) sugars simultaneously.  This strategy revealed interesting epistatic interactions and challenges, and we are continuing to leverage our automation resources to further improve this strain.  The resultant C5/C6 farnesene-producing yeast strain has been shown to make farnesene using cellulosic feedstocks at pilot plant scale.  This opens the possibility to use non-food plant biomass to generate both advanced fuels and petroleum replacement chemicals.