 "S. stipitis" is a predominantly haploid yeast but strains can be induced to mate with themselves or with other strains of "S. stipitis" by cultivating cells on minimal medium containing limiting amounts of carbon sources and nitrogen.An extensive genetic toolbox has been developed for "S. stipitis" that includes synthetic drug resistance markers for nourseothricin acetyltransferase gene (nat1), hygromycin (hph) and a synthetic form of Cre that enables excision of the markers.Engineered strains of "S. stipitis" will produce 57 g/l ethanol from pure xylose in under 48 h and adapted strains will produce significant amounts of ethanol from acid hydrolysates of lignocellulose.