There is provided an engineered host cells comprising (a) one or more mutations in one or more endogenous genes encoding a protein associated with iron metabolism; and (b) at least one gene encoding a polypeptide having xylose isomerase activity, and methods of their use thereof.
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was funded, in part, by the United States government under a grant with the Department of Energy, Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office, Award No. DE-FC36-08GO18103 to Mascoma and FWP#CEEB007 to Oak Ridge National Laboratory. This invention was also funded, in part, by the Bioenergy Science Center, Oak Ridge National Laboratory, a U.S. Department of Energy Bioenergy Research Center supported by the Office of Biological and Environmental Research, under contract DE-P502-06ER64304. The government has certain rights in the invention.