Authors: João R M Almeida Magnus Bertilsson Bärbel HahnHägerdal Gunnar Lidén MarieF GorwaGrauslund
Publish Date: 2009/06/09
Volume: 84, Issue: 4, Pages: 751-761
Abstract
Industrial Saccharomyces cerevisiae strains able to utilize xylose have been constructed by overexpression of XYL1 and XYL2 genes encoding the NADPHpreferring xylose reductase XR and the NAD+dependent xylitol dehydrogenase XDH respectively from Pichia stipitis However the use of different cofactors by XR and XDH leads to NAD+ deficiency followed by xylitol excretion and reduced product yield The furaldehydes 5hydroxymethylfurfural HMF and furfural inhibit yeast metabolism prolong the lag phase and reduce the ethanol productivity Recently genes encoding furaldehyde reductases were identified and their overexpression was shown to improve S cerevisiae growth and fermentation rate in HMF containing media and in lignocellulosic hydrolysate In the current study we constructed a xyloseconsuming S cerevisiae strain using the XR/XDH pathway from P stipitis Then the genes encoding the NADH and the NADPHdependent HMF reductases ADH1S110PY295C and ADH6 respectively were individually overexpressed in this background The performance of these strains which differed in their cofactor usage for HMF reduction was evaluated under anaerobic conditions in batch fermentation in absence or in presence of HMF In anaerobic continuous culture carbon fluxes were obtained for simultaneous xylose consumption and HMF reduction Our results show that the cofactor used for HMF reduction primarily influenced formation of products other than ethanol and that NADHdependent HMF reduction influenced product formation more than NADPHdependent HMF reduction In particular NADHdependent HMF reduction contributed to carbon conservation so that biomass was produced at the expense of xylitol and glycerol formation
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