Enhancement of xylose transport in saccharomyces cerevisiae by transformation of GXF1, a xylose transporter gene, from candida intermedia

Abstract

Rising of energy costs and the increased awareness of global warming have inspired production of renewable, biomass-derived chemicals and fuels. Plant biomass is potentially an inexhaustible source of bioenergy. To produce the fuel for the motor vehichles, industrial bioethanol production from cheap renewable lignocellulosic substrates has been regarded as an important attempt. However, efficient production of bioethanol is attributed to the ability of microbial cell to utilize the abundant glucose and pentose sugar present in lignocellulosic biomass. Because of the lack of xylose transporter in wild S. cerevisiae, they are unable to utilize xylose sugar which is the second most abundant sugar in lignocellulosic biomass. Several successful researches have been performed in Sachharomyces cerevisiae to induce efficient xylose transport, and xylose fermentation. One of the limiting steps in xylose fermentation is the xylose transportation step. Different xylose transporter encoding gene are naturally occurring in several species, the integration of those xylose transporting genes in Sachharomyces cerevisiae would led to the transportation of xylose inside the cells. GXF1 is the glucose/xylose faciliator occurring in fungus Candida intermedia which transports the xylose by facilitated diffusion. The yeast cloned with GXF1 xylose transporter, in the present study, has been shown for improved xylose growth kinetics (specific growth rate, µ = 0.02 hr -1 and xylose transporting phenotypes compared to the control cells. However, very less amount of ethanol production 0.09mg/ml is found which might be due to lack of xylose metabolizing pathways in wild yeasts. The aim of this resarch is the heterologous expression of GXF1 in Sachharomyces cerevisiae for efficient xylose transport inside the cell for the production of bioethanol. Good xylose transport kinetics has been shown by the expression of GXF1, however, ethanol production is quite impossible by just expression of transporter gene, as yeast lacks xylose metabolizing pathways too. Hence further improvement of the strain with the xylose metabolizing pathways is believed to uplift the production of bioethanol from cheap lignocellulosic substrates.

Keywords: Transformation, Sachharomyces cerevisiae, Candida intermedia, GXF1, xylose transporter, Bioethanol.