Xylose fermentation by yeasts. 5. Use of ATP balances for modeling oxygen‐limited growth and fermentation of yeast Pichia stipitis with xylose as carbon source

Abstract

Kinetic studies are presented for the growth and fermentation of the yeast Pichia stipitis with xylose as the carbon source. Ethanol is produced from xylose under anaerobic as well as under oxygen-limiting conditions but only at dissolved oxygen concentrations up to 3 mumol/L Maximum yields and production rates were obtained under oxygen-limiting conditions, where the xylose metabolism may be considered to be consisted of three different components (assimilation, respiration, fermentation). The contribution of each pathway is determined by the availability of oxygen and the energy yield of each pathway. In order to describe the course of oxygen-limited fermentations, a mathematical model has been developed with the assumption that growth is coupled to the energy production. The resulting model requires only four independent parameters (Y(x/O(2) ), Y(ATP) (max), m(ATP), and P/O). These parameters were estimated on the basis of eight separate batch fermentations.

Metabolic pathway analysis of Scheffersomyces (Pichia) stipitis: effect of oxygen availability on ethanol synthesis and flux distributions

“…Examining the S. stipitis metabolic network under varying levels of oxygen availability through elementary mode analysis suggested that low oxygen transfer favored ethanol production. This prediction was also in agreement with previous fermentation studies of S. stipitis (Rizzi et al 1989;Skoog et al 1992;Klinner et al 2005) showing S. stipitis requiring oxygen-limited condition for an efficient production of ethanol. The optimal aeration with maximum ethanol production observed in this study was similar to the value reported by Furlan et al (1994), Taniguchi et al (1997), andSilva et al (2010).…”

Molecular Basis for Anaerobic Growth of Saccharomyces cerevisiae on Xylose, Investigated by Global Gene Expression and Metabolic Flux Analysis

“…The maximum specific rate of growth, in contrast, was dramatically lower on xylose (Table 6). This indicates that there is a kinetic problem, which may involve uptake and/or catabolism of xylose or an insufficient rate of ATP production to support growth, as hypothesized previously (30). The averages Ϯ standard deviations from a DNA microarray analysis of two independent cultures are shown.…”

“…While the specific ATP production rate 3.7 mmol of ATP g of biomass Ϫ1 h Ϫ1 was sufficient in C1, a rate of 1.8 mmol of ATP g of biomass Ϫ1 h Ϫ1 in TMB3001 when acetoin was added was apparently insufficient (48). Since the amount of ATP that is necessary to just sustain the viability of the existing cell mass, the so-called maintenance energy, is about 1.2 mmol of ATP g of biomass Ϫ1 h Ϫ1 in oxygen-limited P. stipitis cultures grown on xylose alone (30), it appears that at least 2 mmol of ATP g of biomass Ϫ1 h Ϫ1 must be generated from the catabolism of xylose to enable anaerobic growth.…”

Molecular cloning of alcohol dehydrogenase genes of the yeastPichia stipitis and identification of the fermentative ADH

“…The enzymes of the respiratory chain of P. stipitis are not repressed in response to oxygen limitation and even not under aerobic conditions (Passoth et al, 1996). The specific growth rate drastically decreases at oxygen limitation (for instance Bruinenberg et al, 1984;Dellweg et al, 1984;Rizzi et al, 1989;Skoog et al, 1992b). Therefore, this organism cannot be regarded as a facultative anaerobic yeast but as a facultative fermentative one (Visser et al, 1990).…”

“…stipitis produces ethanol from glucose or xylose at low dissolved oxygen concentrations (Bruinenberg et al, 1984;Rizzi et al, 1989). However, this yeast is also able to reassimilate ethanol under the same conditions.…”