Abstract: The present invention confers to the ferementative yeast Saccharomyces cerevisiae, genetically modified by insertion of a nucleic acid sequence encoding a xylose and a glucose active transporter, the ability to assimilate xylose using a system of co-transport with protons exhibiting a high affinity for xylose. The invention is useful for the production of bioethanol from plant biomass and other lignocellulosic materials, using genetically modified microorganisms for assimilating and fermenting xylose in mixtures of hexoses and pentoses resulting from raw material of industrial interest.