Patent ID: 8735138

Claim:
A method of producing a strain of Saccharomyces that is capable of growing at a desired growth rate using xylose as a sole carbon source, the method comprising: (a) providing a population of genetically diverse nonrecombinant yeast cells of the genus Saccharomyces; (b) culturing the yeast cells under conditions that permit combining of DNA between the yeast cells; (c) screening or selecting the yeast cells by incubating the yeast cells on or in xylose-containing medium for a time sufficient to permit yeast cells capable of growing on xylose-containing medium to grow; and (d) isolating one or more of the screened or selected yeast cells having a growth rate of at least one generation per 48 hours using xylose as a sole carbon source, wherein steps (b) and (c) are optionally repeated until one or more yeast cells having a growth rate of at least one generation per 48 hours can be isolated.