Metabolomic and ¹³C‐metabolic flux analysis of a xylose‐consuming Saccharomyces cerevisiae strain expressing xylose isomerase

Abstract

Over the past two decades significant progress has been made in the engineering of xylose-consuming Saccharomyces cerevisiae strains for production of lignocellulosic biofuels. However, the ethanol productivities achieved on xylose are still significantly lower than those observed on glucose for reasons that are not well understood. We have undertaken an analysis of central carbon metabolite pool sizes and metabolic fluxes on glucose and on xylose under aerobic and anaerobic conditions in a strain capable of rapid xylose assimilation via xylose isomerase in order to investigate factors that may limit the rate of xylose fermentation. We find that during xylose utilization the flux through the non-oxidative PPP is high but the flux through the oxidative PPP is low, highlighting an advantage of the strain employed in this study. Furthermore, xylose fails to elicit the full carbon catabolite repression response that is characteristic of glucose fermentation in S. cerevisiae. We present indirect evidence that the incomplete activation of the fermentation program on xylose results in a bottleneck in lower glycolysis, leading to inefficient re-oxidation of NADH produced in glycolysis.

Functional expression and evaluation of heterologous phosphoketolases in Saccharomyces cerevisiae

“…The substrate specificities of Xfpk(LM) and Xfpk(CA) appear to be very similar, while the specificity of Xfpk(BB) towards F6P was considerably higher than for the other two candidates, making it an interesting enzyme candidate to evaluate in vivo where intracellular concentrations of F6P should be significantly higher than of X5P during glucose conditions (Wasylenko and Stephanopoulos 2015). …”

Complete genome sequence, metabolic model construction and phenotypic characterization of Geobacillus LC300, an extremely thermophilic, fast growing, xylose-utilizing bacterium

“…Recently, the Stephanopoulos lab developed several efficient yeast strains for xylose utilization. S. cerevisiae strain H131-A3-AL is reported to have maximum growth rates of 0.23 h −1 and 0.20 h −1 under aerobic and anaerobic conditions, respectively, and specific xylose utilization rates of 1.50 g/g/h and 1.87 g/g/h, respectively (Wasylenko and Stephanopoulos, 2014; Zhou et al, 2012). Thus, compared to these strains, Geobacillus LC300 has a xylose utilization rate that is 3-times higher than the best metabolically engineered S. cerevisiae strain to date, and grows 3-times faster than E. coli on xylose under its optimal growth conditions.…”

Combining C6 and C5 sugar metabolism for enhancing microbial bioconversion

“…For instance, the overall performance of the oxidoreductase pathway was significantly improved under anaerobic conditions when coupling with a reductive acetate metabolic pathway [25 ]. In addition, a recent report indicated that xylose cannot fully activate the fermentation process as well as glucose, which may lead to a lower glycolytic bottleneck and lower ethanol yield from xylose [26]. More efforts are required for tackling this fundamental problem.…”