Combining Xylose Reductase from Spathaspora arborariae with Xylitol Dehydrogenase from Spathaspora passalidarum to Promote Xylose Consumption and Fermentation into Xylitol by Saccharomyces cerevisiae

In recent years, many novel xylose-fermenting yeasts belonging to the new genus Spathaspora have been isolated from the gut of wood-feeding insects and/or wood-decaying substrates. We have cloned and expressed, in Saccharomyces cerevisiae, a Spathaspora arborariae xylose reductase gene (SaXYL1) that accepts both NADH and NADPH as co-substrates, as well as a Spathaspora passalidarum NADPH-dependent xylose reductase (SpXYL1.1 gene) and the SpXYL2.2 gene encoding for a NAD+-dependent xylitol dehydrogenase. These enzymes were co-expressed in a S. cerevisiae strain over-expressing the native XKS1 gene encoding xylulokinase, as well as being deleted in the alkaline phosphatase encoded by the PHO13 gene. The S. cerevisiae strains expressing the Spathaspora enzymes consumed xylose, and xylitol was the major fermentation product. Higher specific growth rates, xylose consumption and xylitol volumetric productivities were obtained by the co-expression of the SaXYL1 and SpXYL2.2 genes, when compared with the co-expression of the NADPH-dependent SpXYL1.1 xylose reductase. During glucose-xylose co-fermentation by the strain with co-expression of the SaXYL1 and SpXYL2.2 genes, both ethanol and xylitol were produced efficiently. Our results open up the possibility of using the advantageous Saccharomyces yeasts for xylitol production, a commodity with wide commercial applications in pharmaceuticals, nutraceuticals, food and beverage industries

Brazilian potential for biomass ethanol: Challenge of using hexose and pentose cofermenting yeast strains

918-926This paper reviews Brazilian scenario and efforts for deployment of technology to produce bioethanol vis-à-vis recent international advances in the area, including possible use of hexose and pentose co-fermenting yeast strains

Molecular Analysis of Maltotriose Active Transport and Fermentation by Saccharomyces cerevisiae Reveals a Determinant Role for the AGT1 Permease▿

Incomplete and/or sluggish maltotriose fermentation causes both quality and economic problems in the ale-brewing industry. Although it has been proposed previously that the sugar uptake must be responsible for these undesirable phenotypes, there have been conflicting reports on whether all the known α-glucoside transporters in Saccharomyces cerevisiae (MALx1, AGT1, and MPH2 and MPH3 transporters) allow efficient maltotriose utilization by yeast cells. We characterized the kinetics of yeast cell growth, sugar consumption, and ethanol production during maltose or maltotriose utilization by several S. cerevisiae yeast strains (both MAL constitutive and MAL inducible) and by their isogenic counterparts with specific deletions of the AGT1 gene. Our results clearly showed that yeast strains carrying functional permeases encoded by the MAL21, MAL31, and/or MAL41 gene in their plasma membranes were unable to utilize maltotriose. While both high- and low-affinity transport activities were responsible for maltose uptake from the medium, in the case of maltotriose, the only low-affinity (Km, 36 ± 2 mM) transport activity was mediated by the AGT1 permease. In conclusion, the AGT1 transporter is required for efficient maltotriose fermentation by S. cerevisiae yeasts, highlighting the importance of this permease for breeding and/or selection programs aimed at improving sluggish maltotriose fermentations

Increasing Ethanol Tolerance and Ethanol Production in an Industrial Fuel Ethanol <i>Saccharomyces cerevisiae</i> Strain

The stress imposed by ethanol to Saccharomyces cerevisiae cells are one of the most challenging limiting factors in industrial fuel ethanol production. Consequently, the toxicity and tolerance to high ethanol concentrations has been the subject of extensive research, allowing the identification of several genes important for increasing the tolerance to this stress factor. However, most studies were performed with well-characterized laboratory strains, and how the results obtained with these strains work in industrial strains remains unknown. In the present work, we have tested three different strategies known to increase ethanol tolerance by laboratory strains in an industrial fuel–ethanol producing strain: the overexpression of the TRP1 or MSN2 genes, or the overexpression of a truncated version of the MSN2 gene. Our results show that the industrial CAT-1 strain tolerates up to 14% ethanol, and indeed the three strategies increased its tolerance to ethanol. When these strains were subjected to fermentations with high sugar content and cell recycle, simulating the industrial conditions used in Brazilian distilleries, only the strain with overexpression of the truncated MSN2 gene showed improved fermentation performance, allowing the production of 16% ethanol from 33% of total reducing sugars present in sugarcane molasses. Our results highlight the importance of testing genetic modifications in industrial yeast strains under industrial conditions in order to improve the production of industrial fuel ethanol by S. cerevisiae

Volumes 106, Number 1 - 3 Spring 2003, ISSN: 0273--2289

The kinetics and regulation of D-xylose uptake were investigated in the efficient pentose fermentor Candida succiphila, and in Kluyveromyces marxianus,which assimilate butdonotfermentpentose sugars. Activehighaffinity (K m ~ 3.8 mM; V max ~ 15 nmol/[mgmin]) and putative facilitated diffusion low-affinity (K m ~ 140 mM; V max ~ 130 nmol/[mgmin]) transport activities were found in C. succiphila grown, respectively, on xylose or glucose

Bioactive Compounds from and against Yeasts in the One Health Context: A Comprehensive Review

Yeasts are the most used microorganisms for biotechnological purposes. Although they have been mainly recognized for their application in the beverage and bioethanol industries, these microorganisms can be efficiently employed in pharmaceutical and food production companies. In these industrial sectors, yeasts are highly desirable for their capacity to produce bioactive compounds from simple substrates, including wastes. In this review, we present the state of the art of bioactive compound production in microbial cell factories and analyze the avenues to increase the productivity of these molecules, which benefit human and environmental health. The article addresses their vast biological activities, from preventing to treating human diseases and from pre to postharvest control on agroindustrial streams. Furthermore, different yeast species, genetically engineered or not, are herein presented not only as biofactories of the referred to compounds but also as their targets. This comprehensive analysis of the literature points out the significant roles of biodiversity, bioprospection, and genome editing tools on the microbial production of bioactive compounds and reveals the value of these approaches from the one health perspective