Minimizing the cost of cellulosic-biomass-derived Amyris Diesel by combining non-native sugar catabolism and xylose isomerase pathways

Amyris is a synthetic biology company dedicated to providing high-performance alternatives to petroleum-sourced fuels and chemicals. Amyris’s technology platform centers on fermentation of sugars by yeast to produce a class of hydrocarbons known as isoprenoids. The isoprenoid farnesene is a C15, branched alkene that can be hydrogenated to farnesane, a drop-in, renewable diesel fuel approved by the U.S. EPA up to a 35% blend. As part of the DOE-funded National Advanced Biofuels Consortium, Amyris has been developing a pilot-ready process for using lignocellulosic sugar streams in farnesene manufacturing. At least two biological challenges remain for commercializing cellulosic hydrolysates as a feedstock for farnesene production. These are 1) converting sugars to farnesene more efficiently than is possible using native metabolism, to achieve the lowest possible cost of production and 2) engineering Amyris’s yeast to consume xylose, as S. cerevisiae doesn’t normally eat this abundant hemicellulosic sugar.

Here we report on Amyris’s progress towards commercializing biofuels from cellulosic sugars, specifically in overcoming these two hurdles. First we show that, by re-routing sugar catabolism through two independent heterologous pathways, and by altering redox cofactor usage in isoprenoid biosynthesis, we can increase theoretical yields of farnesene by 20% (per sugar) and by 170% (per oxygen) relative to native metabolism. Secondly, we demonstrate xylose consumption in strains with this synthetic carbon metabolism via introduction of a heterologous xylose isomerase. Using strains so improved, we will describe the successful production of farnesene suitable for use as a diesel fuel from corn stover hydrolysate in pilot-scale fermentations.