Kinetics of ethanol production from D‐xylose by the yeastpichia stipitis

Abstract

Pichia stipitis (CBS 5773) most efficiently ferments the sugar mixture from acid hydrolysed spent brewer's grains, whereby D-xylose and D-galactose (but not L-arabinose) are consumed simultaneously, after the D-glucose had been used up from the mixture. The key enzymes, xylose reductase (Xyl-R) and xylitol dehydrogenase (Xit-DH) are inducible and cannot be found in glucose-grown cells. Purified Xyl-R was shown to use both NADH and NADPH as coenzyme, and model simulations showed that under aerobic physiological conditions NADPH is preferred (95%), whereas under oxygen deficiency 85% of xylose are reduced by NADH. Xit-DH seems to use only NAD + as coenzyme, and the reaction is competitively inhibited by NADH. According to the equilibrium constants for Xyl-R (5,5·10 9 1·Mol -1 ) and for Xit-DH (6,9·10 -11 Mol·1 -1 ) the equlibria of both reactions are distinctly shifted to xylitol, which may be excreted into the medium, especially when in the absence of oxygen a surplus of NADH cannot be dehydrogenated.

Flux balance analysis predicts NADP phosphatase and NADH kinase are critical to balancing redox during xylose fermentation inScheffersomyces stipitis

“…In contrast, Ligthelm et al (1988c) used nuclear magnetic resonance (NMR) spectroscopy and 13 C labelling to infer that NADH is the preferred XR cofactor during anaerobic conditions. Dellweg et al (1990) corroborated their conclusions via metabolic flux analysis and predicted that NADPH is preferred by XR aerobically. Dellweg et al (1990) suggested the concentration of redox cofactors may exert metabolic control over the in vivo XR cofactor preference.…”

“…Dellweg et al (1990) corroborated their conclusions via metabolic flux analysis and predicted that NADPH is preferred by XR aerobically. Dellweg et al (1990) suggested the concentration of redox cofactors may exert metabolic control over the in vivo XR cofactor preference. The conflicting conclusions for the in vivo XR preference inferred from in vitro enzyme activities and model-based analysis require a reexamination of the assumptions made during the pre-genomic age.…”

“…These yeasts demonstrate that NAD(P)H-dependent XR enables xylose fermentation to ethanol, but NADPH-dependent XR and NADPase/NADH kinase still accumulate xylitol (Bruinenberg et al, 1984). Further investigation is needed to determine if our proposed mechanism can support sustained anaerobic fermentation with an entirely imbalanced pathway, or if other factors, such as inhibition of XR or XDH by NAD(P)(H) (Verduyn et al, 1985b;Dellweg et al, 1990), limit its ability in vivo. Our analysis of xylose fermentation in S. stipitis highlights the need to understand and engineer metabolism at a systems-level, which has been advocated by Kim et al (2011) and Meadows et al (2016).…”

Xylose fermentation by Saccharomyces cerevisiae

“…1C, D; Dellweg et al 1990;Skoog and Hahn-H~tgerdal 1990;Prior et al 1989) regardless of the growth conditions. Model simulations predict that in P. stipitis under aerobic conditions N A D P H is the preferred cofactor for XR, whereas under oxygen deficiency xylose is reduced by NADH (Dellweg et al 1990;Rizzi et al 1988;Dellweg et al 1989). The absence of xylitol accumulation under oxidative conditions could be interpreted as a result of xylitol oxidation.…”

Utilização da levedura Pichia stipitis UFMG-IMH 43.2 para obtenção de etanol em hidrolisado hemicelulósico de bagaço de cana-de-açúcar

“…Entretanto, a taxa de hidrólise é ainda considerada baixa CHENG, 2002;BINOD et al, 2010). RODMAN, 2002;SARROUH et al, 2007;KUMAR et al, 2009;GÍRIO et al, 2010;TALEBNIA;KARAKASHEV;ANGELIDAKI, 2010 PRIOR, 1986;DELLWEG et al, 1990;AGBOGBO et al, 2006;VAN MARIS et al, 2006;GÍRIO et al, 2010).…”