Characterization of the xylose-transporting properties of yeast hexose transporters and their influence on xylose utilization.
For an economically feasible production of ethanol from plant biomass by microbial cells, the fermentation of xylose is important. As xylose uptake might be a limiting step for xylose fermentation by recombinant xylose-utilizing Saccharomyces cerevisiae cells a study of xylose uptake was performed. After deletion of all of the 18 hexose-transporter genes, the ability of the cells to take up and to grow on xylose was lost. Reintroduction of individual hexose-transporter genes in this strain revealed that at intermediate xylose concentrations the yeast high- and intermediate-affinity transporters Hxt4, Hxt5, Hxt7 and Gal2 are important xylose-transporting proteins. Several heterologous monosaccharide transporters from bacteria and plant cells did not confer sufficient uptake activity to restore growth on xylose. Overexpression of the xylose-transporting proteins in a xylose-utilizing PUA yeast strain did not result in faster growth on xylose under aerobic conditions nor did it enhance the xylose fermentation rate under anaerobic conditions. The results of this study suggest that xylose uptake does not determine the xylose flux under the conditions and in the yeast strains investigated.
Hamacher
Tanja
T
Institut für Mikrobiologie, Heinrich-Heine-Universität, Universitätsstr. 1, Geb. 26.12.01, D-40225 Düsseldorf, Germany1.
Becker
Jessica
J
Institut für Mikrobiologie, Heinrich-Heine-Universität, Universitätsstr. 1, Geb. 26.12.01, D-40225 Düsseldorf, Germany1.
Gárdonyi
Márk
M
Department of Applied Microbiology, Lund University, 22100 Lund, Sweden2.
Hahn-Hägerdal
Bärbel
B
Department of Applied Microbiology, Lund University, 22100 Lund, Sweden2.
Boles
Eckhard
E
Institut für Mikrobiologie, Heinrich-Heine-Universität, Universitätsstr. 1, Geb. 26.12.01, D-40225 Düsseldorf, Germany1.
D000693:Anaerobiosis; D001692:Biological Transport; D005285:Fermentation; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D006601:Hexoses / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism*
D006601:Hexoses; D009004:Monosaccharide Transport Proteins; D014994:Xylose