초록
<P><B>Background</B></P><P>Poly-3-<SMALL>D</SMALL>-hydroxybutyrate (PHB) that is a promising precursor for bioplastic with similar physical properties as polypropylene, is naturally produced by several bacterial species. The bacterial pathway is comprised of the three enzymes β-ketothiolase, acetoacetyl-CoA reductase (AAR) and PHB synthase, which all together convert acetyl-CoA into PHB. Heterologous expression of the pathway genes from <I>Cupriavidus necator</I> has enabled PHB production in the yeast <I>Saccharomyces cerevisiae</I> from glucose as well as from xylose, after introduction of the fungal xylose utilization pathway from <I>Scheffersomyces stipitis</I> including xylose reductase (XR) and xylitol dehydrogenase (XDH). However PHB titers are still low.</P><P><B>Results</B></P><P>In this study the acetoacetyl-CoA reductase gene from <I>C. necator</I> (CnAAR), a NADPH-dependent enzyme, was replaced by the NADH-dependent AAR gene from <I>Allochromatium vinosum</I> (AvAAR) in recombinant xylose-utilizing <I>S. cerevisiae</I> and PHB production was compared. <I>A. vinosum</I> AAR was found to be active in <I>S. cerevisiae</I> and able to use both NADH and NADPH as cofactors. This resulted in improved PHB titers in <I>S. cerevisiae</I> when xylose was used as sole carbon source (5-fold in aerobic conditions and 8.4-fold under oxygen limited conditions) and PHB yields (4-fold in aerobic conditions and up to 5.6-fold under oxygen limited conditions). Moreover, the best strain was able to accumulate up to 14% of PHB per cell dry weight under fully anaerobic conditions.</P><P><B>Conclusions</B></P><P>This study reports a novel approach for boosting PHB accumulation in <I>S. cerevisiae</I> by replacement of the commonly used AAR from <I>C. necator</I> with the NADH-dependent alternative from <I>A. vinosum</I>. Additionally, to the best of our knowledge, it is the first demonstration of anaerobic PHB synthesis from xylose.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s12934-016-0598-0) contains supplementary material, which is available to authorized users.</P>