The yeast Saccharomyces cerevisiae is not capable of metabolizing xylose. In attempts to confer xylose utilization ability in S. cerevisiae, a number of xylose isomerase (XI) genes have been expressed in this yeast. While several of these genes were expressed in S. cerevisiae, the need still exists for a strain with improved xylose utilization ability for the production of bioethanol. Satoshi Katahira of the Toyota Central R&D Labs in Japan led the search for novel XI genes from the protists residing in the hindgut of the termite, Reticulitermes speratus.
Eight novel XI genes were obtained from the protists of the R. speratus hindgut. The gene that exhibited the highest XI activity was then expressed in S. cerevisiae. Growth rate and the xylose consumption rate of the S. cerevisiae strain expressing the novel XI were found to be superior to strains with the other seven genes, as well as the control strains.
A novel XI gene conferring superior xylose consumption in S. cerevisiae was successfully isolated from the protists in the termite hindgut. Isolation of this XI gene might contribute to improving the productivity of industrial bioethanol.