A xylose-utilizing oleaginous Saccharomyces cerevisiae and a rapid near-infrared scanning methodology for lipids

Historically Saccharomyces cerevisiae is not known for being oleaginous. We screened several industrial strains for their ability to accumulate internal lipids under nitrogen limiting conditions and found one, S. cerevisiae D5A, that natively accumulated lipids in excess of 20% of its dry cell weight (dcw). We further engineered this diploid strain to accumulate lipids in excess of 30% dcw using genetic knock-outs. To fully utilize sugars released from pretreated terrestrial biomass, we also engineered in utilization of xylose via the xylose reductase and xylitol dehydrogenase pathway from Pichia stipitis with over-expression of the native S. cerevisiae xylulose kinase. Our strain, BFY709, accumulates in excess of 35% lipids from xylose as the sole carbon source. Determining the lipid content of microbes is laborious and time consuming, thus we developed a rapid and robust methodology for use of near-infrared to screen freeze-dried yeast biomass in a 96-well microtiter plate format to determine lipid content. Compared to our standard wet-chemistry lipid extraction and analysis (in-situ FAME analysis), NIR scanning is 90-95% accurate for dcw lipid content in yeast.