D-Xylose Utilization by Saccharomyces cerevisiae

Abstract

Although it is generally accepted that Saccharomyces cerevisiae is unable to assimilate D-XylOSe, four strains were found to utilize xylose aerobically at different efficiencies in the presence of a mixture of substrates. The degree of D-xylose utilization by S. cerevisiae ATCC 26602 depended upon the presence of other substrates or yeast extract. The greatest amount of xylose (up to 69% over 7 d) was utilized when sugar substrates such as D-ribose were co-metabolized. Much lower degrees of utilization occurred with co-metabolism of organic acids, polyols or ethanol. A mixture of D-glucose, D-ri bose, D-raffinose, glycerol and D-xylose resulted in greater xylose utilization than the presence of a single substrate and xylose. The absence of growth on a co-substrate alone did not prevent the utilization of xylose in its presence. Xylose was co-metabolized with ribose under anaerobic conditions but at a much slower rate than under aerobic conditions. When [ 14C]xylose was utilized in the presence of ribose under anaerobic conditions, the radioactive label was detected mainly in xylitol and not in the small amounts of ethanol produced. Under aerobic conditions the radioactive label was distributed between xylitol(91.3 0-8%), COz (2.6 & 2.3%) and biomass (1.7 & 0.6%). No other metabolic products were detected. Whereas most xylose was dissimilated rather than assimilated by S. cerevisiae, the organism apparently possesses a pathway which completely oxidizes xylose in the presence of another substrate.

Cloning and Characterization of the xyl1 Gene, Encoding an NADH-Preferring Xylose Reductase from Candida parapsilosis , and Its Functional Expression in Candida tropicalis

“…Glycerol is generally produced during anaerobic fermentation to oxidize excess NADH (48). The decrease in ethanol and glycerol formation is probably due to the consumption of reduction equivalents in the XR reaction rather than in the alcohol dehydrogenase or glycerophosphate dehydrogenase reaction and to the supply of reduction equivalents by anaerobic ethanol oxidation (40,57). Glycerol and ethanol accumulation during the culture period represents a serious problem for the purification of xylitol from the fermentation broth.…”

Improved sugar co-utilisation by encapsulation of a recombinant Saccharomyces cerevisiae strain in alginate-chitosan capsules

“…One of the main problems is the issue of inhibitors produced during the pretreatment and hydrolysis of the raw material into fermentable sugars. Another problem is the fact that pentoses are not fermentable by wild-type Saccharomyces cerevisiae [2], although there are a few exceptional cases of slow consumption [3]. The most popular approach to this problem has been to create recombinant strains of S. cerevisiae utilising xylose, arabinose or a mixture of the two [4].…”

Putative xylose and arabinose reductases in Saccharomyces cerevisiae

“…Most of the 116 yeasts investigated converted arabinose to arabitol, and seven of the strains tested produced ethanol from arabinose. S. cerevisiae has previously been shown not to grow with arabinose as the sole carbon source (van Zyl et al , 1989). The genes of the araBAD operon of E. coli have been expressed in S. cerevisiae with the aim to create an arabinose‐fermenting strain (Sedlak and Ho, 2001).…”