A xylose-utilizing oleaginous Saccharomyces cerevisiae as a platform for biofuels production

Saccharomyces cerevisiae is a well-known, genetically-tractable yeast which has been used at the industrial scale for centuries; however, it 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 strain, S. cerevisiae D5A that accumulated lipids in excess of 20% of its dry cell weight (dcw).  We further engineered this diploid strain to accumulate lipids up to 50% dcw using a combination of genetic knock-out and over-expression of key lipid pathway enzymes.  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 stipites, with over-expression of the native S. cerevisiae xylulose kinase.  Our strain, BFY742, accumulates 50% dcw lipids from xylose as the sole carbon source. In addition, we over-expressed a single fatty alcohol reductase gene to produce C16 and C18 fatty alcohols from S. cerevisiae.  Accumulation of lipids and fatty alcohols occurred with the concomitant production of ethanol showing the breadth of products and potential of S. cerevisiae as platform fuels yeast.