초록
<P><B>Background</B></P><P>Pectin-rich wastes, such as citrus pulp and sugar beet pulp, are produced in considerable amounts by the juice and sugar industry and could be used as raw materials for biorefineries. One possible process in such biorefineries is the hydrolysis of these wastes and the subsequent production of ethanol. However, the ethanol-producing organism of choice, <I>Saccharomyces cerevisiae</I>, is not able to catabolize <SMALL>D</SMALL>-galacturonic acid, which represents a considerable amount of the sugars in the hydrolysate, namely, 18 % (w/w) from citrus pulp and 16 % (w/w) sugar beet pulp.</P><P><B>Results</B></P><P>In the current work, we describe the construction of a strain of <I>S. cerevisiae</I> in which the five genes of the fungal reductive pathway for <SMALL>D</SMALL>-galacturonic acid catabolism were integrated into the yeast chromosomes: <I>gaa</I>A, <I>gaa</I>C and <I>gaa</I>D from <I>Aspergillus niger</I> and <I>lgd</I>1 from <I>Trichoderma reesei,</I> and the recently described <SMALL>D</SMALL>-galacturonic acid transporter protein, <I>gat</I>1, from <I>Neurospora crassa</I>. This strain metabolized <SMALL>D</SMALL>-galacturonic acid in a medium containing <SMALL>D</SMALL>-fructose as co-substrate.</P><P><B>Conclusion</B></P><P>This work is the first demonstration of the expression of a functional heterologous pathway for <SMALL>D</SMALL>-galacturonic acid catabolism in <I>Saccharomyces cerevisiae</I>. It is a preliminary step for engineering a yeast strain for the fermentation of pectin-rich substrates to ethanol.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s12934-016-0544-1) contains supplementary material, which is available to authorized users.</P>