1-02: Conversion of lignocellulosic biomass to fuel and food using a non-recombinant Saccharomyces cerevisiae selectively bred to metabolize xylose

Saccharomyces cerevisiae is the most important industrial yeast species employed in brewing, winemaking, ethanol production, baking and an array of other applications including food, health and animal nutrition.  S. cerevisiae has found such widespread use because it is a safe and highly efficient converter of six-carbon sugars (glucose and fructose) into ethanol and carbon dioxide. Whilst most research efforts have focused on genetic engineering techniques to generate organisms for lignocellulosic ethanol production, we have used natural breeding and selection to generate strains of S. cerevisiae that metabolize xylose as a sole carbon source, as well as being able to ferment cellulose-derived glucose.  There is a general view that all the sugars in biomass must be converted to ethanol in order for lignocellulose to be an economically viable substrate for the manufacture of biofuel.  We contend that there is a distinct advantage in providing for economic fuel production whilst also diluting the “food versus fuel” argument that is often used against biofuels.  We have therefore developed our yeast strains so that they can grow with 90% efficiency on sugars and other carbon released from hydrolyzed hemicellulose, as well as ferment cellulosic glucose to achieve 10%v/v or more ethanol. The yeasts are robust enough to operate in non-detoxified hydrolyzates, significantly reduce the chemical and biological oxygen demands of waste water streams and, because they are non-genetically engineered, can be used in the ethanol production process with any excess yeast biomass used as a protein supplement to animal feeds.