Competition between pentoses and glucose during uptake and catabolism in recombinant Saccharomyces cerevisiae

Abstract

BackgroundIn mixed sugar fermentations with recombinant Saccharomyces cerevisiae strains able to ferment D-xylose and L-arabinose the pentose sugars are normally only utilized after depletion of D-glucose. This has been attributed to competitive inhibition of pentose uptake by D-glucose as pentose sugars are taken up into yeast cells by individual members of the yeast hexose transporter family. We wanted to investigate whether D-glucose inhibits pentose utilization only by blocking its uptake or also by interfering with its further metabolism.ResultsTo distinguish between inhibitory effects of D-glucose on pentose uptake and pentose catabolism, maltose was used as an alternative carbon source in maltose-pentose co-consumption experiments. Maltose is taken up by a specific maltose transport system and hydrolyzed only intracellularly into two D-glucose molecules. Pentose consumption decreased by about 20 - 30% during the simultaneous utilization of maltose indicating that hexose catabolism can impede pentose utilization. To test whether intracellular D-glucose might impair pentose utilization, hexo-/glucokinase deletion mutants were constructed. Those mutants are known to accumulate intracellular D-glucose when incubated with maltose. However, pentose utilization was not effected in the presence of maltose. Addition of increasing concentrations of D-glucose to the hexo-/glucokinase mutants finally completely blocked D-xylose as well as L-arabinose consumption, indicating a pronounced inhibitory effect of D-glucose on pentose uptake. Nevertheless, constitutive overexpression of pentose-transporting hexose transporters like Hxt7 and Gal2 could improve pentose consumption in the presence of D-glucose.ConclusionOur results confirm that D-glucose impairs the simultaneous utilization of pentoses mainly due to inhibition of pentose uptake. Whereas intracellular D-glucose does not seem to have an inhibitory effect on pentose utilization, further catabolism of D-glucose can also impede pentose utilization. Nevertheless, the results suggest that co-fermentation of pentoses in the presence of D-glucose can significantly be improved by the overexpression of pentose transporters, especially if they are not inhibited by D-glucose.

Bioethanol production from coconut husk fiber

“…Consumption of xylose may be explained by the degradation of this pentose during the fermentation process or due to its internalization by endocytosis in the Saccharomyces cerevisiae yeasts, which, although did not metabolize pentoses, are capable of absorbing them internally (SUBTIL & BOLES, 2012). Xylitol content was low and remained constant in relation to those of other compounds.…”

Engineering of yeast hexose transporters to transport d -xylose without inhibition by d -glucose

“…The main hurdle is the competitive inhibition of xylose transport into the cell by glucose (24). To our knowledge, this work is the first to explicitly target transport to work toward cofermentation.…”

“…Although intracellular xylose conversion is only slightly affected by the presence or catabolism of intracellular glucose, xylose transport is strongly inhibited by glucose (24). Avoiding transport inhibition in a cofermentation of cellobiose and xylose showed no impediments but even synergistic effects for a parallel catabolism (25).…”

“…G418 and 0.5 g/L 2-deoxy-D-glucose (2-DOG) were added to select for the AFY10 strain background and prevent growth of suppressor mutants of the hxk 0 phenotype. hxk 0 strains, but not wild-type strains, are resistant to 2-DOG (24). For generation of biomass and for adaptation to growth on xylose, the first three batches were performed in SCE, SCX, and SMX, respectively.…”

Enhancement of Simultaneous Xylose and Glucose Utilization by Regulating ZWF1 and PGI1 in Saccharomyces Cerevisiae

“…Compared with SyBE_Sc122000, both xylose consumption and glucose metabolism were enhanced in SyBE_Sc122009 under all the conditions. Previous research has revealed that the increase in the concentrations of glucose decreased xylose consumption and that hexose transporter overexpression Hxt7 partially relieved the inhibitory effects of increasing glucose concentration [46]. Ishola et al [47,48] reported that glucose concentration affected xylose uptake in SSFF or in reverse membrane bioreactors.…”