Cloning and characterization of sugar transporter genes of Kluyveromyces marxianus GX-UN120

Abstract:

[Background] Kluyveromyces marxianus with a complete xylose metabolic pathway can utilize xylose in lignocellulose. The study of its sugar transporter genes may solve the problem of how to efficiently transport xylose.[Objective] To explore the functions of the sugar transporter genes of K. marxianus GX-UN120 obtained according to the function prediction of KLMA_70145 and KLMA_80101 in K. marxianus DMKU3-1042. [Methods] Km_SUT2 and Km_SUT3 were respectively expressed in Saccharomyces cerevisiae EBY.VW4000. We then observed the growth characteristics of different recombinants in the media with different carbon sources to evaluate the transport capacity of corresponding transporters. [Results] The sugar transporter Km_SUT2 improved the ability of host cells to transport xylose, arabinose, sorbose, ribose, lactose and glucose, while the cells did not have the ability to transport mannose, fructose, sucrose or galactose. Similarly, the sugar transporter Km_SUT3 can transport xylose, arabinose, sorbose, galactose, ribose, lactose and glucose, while it cannot transport mannose or fructose. In the medium with glucose, the utilization of carbon sources by the recombinants was inhibited, while the inhibition on the transport of xylose and ribose by Km_SUT3 was weaker than that by Km_SUT2. [Conclusion] The transporters Km_SUT2 and Km_SUT3 in K. marxianus GX-UN120 can promote the transport of monosaccharides such as xylose. More significantly, Km_SUT3 enables the recombinant to utilize both glucose and xylose under the condition of low glucose concentration, while the transport of xylose by Km_SUT2 is entirely inhibited by glucose.