초록
<P><B>Background</B></P><P>The production of ethanol and other fuels and chemicals from lignocellulosic materials is dependent of efficient xylose conversion. Xylose fermentation capacity in yeasts is usually linked to xylose reductase (XR) accepting NADH as cofactor. The XR from <I>Scheffersomyces</I><I>stipitis</I>, which is able to use NADH as cofactor but still prefers NADPH, has been used to generate recombinant xylose-fermenting <I>Saccharomyces cerevisiae</I>. Novel xylose-fermenting yeasts species, as those from the <I>Spathaspora</I> clade, have been described and are potential sources of novel genes to improve xylose fermentation in <I>S. cerevisiae</I>.</P><P><B>Results</B></P><P>Xylose fermentation by six strains from different <I>Spathaspora</I> species isolated in Brazil, plus the <I>Sp. passalidarum</I> type strain (CBS 10155<SUP>T</SUP>), was characterized under two oxygen-limited conditions. The best xylose-fermenting strains belong to the <I>Sp. passalidarum</I> species, and their highest ethanol titers, yields, and productivities were correlated to higher XR activity with NADH than with NADPH. Among the different <I>Spathaspora</I> species, <I>Sp. passalidarum</I> appears to be the sole harboring two XYL1 genes: <I>XYL1.1</I>, similar to the <I>XYL1</I> found in other <I>Spathaspora</I> and yeast species and <I>XYL1.2</I>, with relatively higher expression level. XYL1.1p and XYL1.2p from <I>Sp. passalidarum</I> were expressed in <I>S. cerevisiae</I> TMB 3044 and XYL1.1p was confirmed to be strictly NADPH-dependent, while XYL1.2p to use both NADPH and NADH, with higher activity with the later. Recombinant <I>S. cerevisiae</I> strains expressing XYL1.1p did not show anaerobic growth in xylose medium. Under anaerobic xylose fermentation, <I>S. cerevisiae</I> TMB 3504, which expresses XYL1.2p from <I>Sp. passalidarum</I>, revealed significant higher ethanol yield and productivity than <I>S. cerevisiae</I> TMB 3422, which harbors XYL1p N272D from <I>Sc. stipitis</I> in the same isogenic background (0.40 vs 0.34 g g<SUB>CDW</SUB><SUP>−1</SUP> and 0.33 vs 0.18 g g<SUB>CDW</SUB><SUP>−1</SUP> h<SUP>−1</SUP>, respectively).</P><P><B>Conclusion</B></P><P>This work explored a new clade of xylose-fermenting yeasts (<I>Spathaspora</I> species) towards the engineering of <I>S. cerevisiae</I> for improved xylose fermentation. The new <I>S. cerevisiae</I> TMB 3504 displays higher XR activity with NADH than with NADPH, with consequent improved ethanol yield and productivity and low xylitol production. This meaningful advance in anaerobic xylose fermentation by recombinant <I>S. cerevisiae</I> (using the XR/XDH pathway) paves the way for the development of novel industrial pentose-fermenting strains.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s13068-016-0570-6) contains supplementary material, which is available to authorized users.</P>