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 ␣-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 highand low-affinity transport activities were responsible for maltose uptake from the medium, in the case of maltotriose, the only low-affinity (K m , 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.Several important industrial applications of the yeast Saccharomyces cerevisiae, such as brewing, baking, and the production of distilled beverages, rely on the efficient fermentation of starch hydrolysates rich in glucose and in the ␣-glucosides maltose and maltotriose. In brewer's wort, for example, the most abundant fermentable sugar is maltose (50 to 60%), followed by maltotriose (15 to 20%) and glucose (10 to 15%). Of these sugars, glucose is preferentially and rapidly utilized by the yeast cells, but process efficiency also requires the complete fermentation of both maltose and maltotriose. After glucose exhaustion, maltose is easily fermented by the majority of S. cerevisiae strains, and not only is maltotriose the least preferred sugar for uptake by these yeast cells, but many yeasts may not use it at all (23, 37, 44). The difficulty that some strains have in consuming maltotriose leads to one of the problems experienced by many breweries, namely, a high content of residual sugar in the finished beer, low ethanol yields, and atypical beer flavor profiles. Therefore, the rate of uptake and fermentation of maltotriose is one of the major determinants of fermentation efficiency and product quality. Due to its relevance for beer fermentation, maltotriose utilization has been studied mostly with the two classes of yeast strains used for brewing, S. cerevisiae ale strains and S. pastorianus lager strains. These studies have revealed that maltotriose utilization by ale strains is significantly slower than that by lager yeasts and that, consequently, residual maltotriose is more common at the end of ale fermentations (22,23,44...

Fuel ethanol is now a global energy commodity that is competitive with gasoline. Using microarray-based comparative genome hybridization (aCGH), we have determined gene copy number variations (CNVs) common to five industrially important fuel ethanol Saccharomyces cerevisiae strains responsible for the production of billions of gallons of fuel ethanol per year from sugarcane. These strains have significant amplifications of the telomeric SNO and SNZ genes, which are involved in the biosynthesis of vitamins B6 (pyridoxine) and B1 (thiamin). We show that increased copy number of these genes confers the ability to grow more efficiently under the repressing effects of thiamin, especially in medium lacking pyridoxine and with high sugar concentrations. These genetic changes have likely been adaptive and selected for in the industrial environment, and may be required for the efficient utilization of biomass-derived sugars from other renewable feedstocks.

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Aims:  We performed an analysis of maltotriose utilization by 52 Saccharomyces yeast strains able to ferment maltose efficiently and correlated the observed phenotypes with differences in the copy number of genes possibly involved in maltotriose utilization by yeast cells. Methods and Results:  The analysis of maltose and maltotriose utilization by laboratory and industrial strains of the species Saccharomyces cerevisiae and Saccharomyces pastorianus (a natural S. cerevisiae/Saccharomyces bayanus hybrid) was carried out using microscale liquid cultivation, as well as in aerobic batch cultures. All strains utilize maltose efficiently as a carbon source, but three different phenotypes were observed for maltotriose utilization: efficient growth, slow/delayed growth and no growth. Through microarray karyotyping and pulsed‐field gel electrophoresis blots, we analysed the copy number and localization of several maltose‐related genes in selected S. cerevisiae strains. While most strains lacked the MPH2 and MPH3 transporter genes, almost all strains analysed had the AGT1 gene and increased copy number of MALx1 permeases. Conclusions:  Our results showed that S. pastorianus yeast strains utilized maltotriose more efficiently than S. cerevisiae strains and highlighted the importance of the AGT1 gene for efficient maltotriose utilization by S. cerevisiae yeasts. Significance and Impact of the Study:  Our results revealed new maltotriose utilization phenotypes, contributing to a better understanding of the metabolism of this carbon source for improved fermentation by Saccharomyces yeasts.

Background: Overflow metabolism is an undesirable characteristic of aerobic cultures of Saccharomyces cerevisiae during biomass-directed processes. It results from elevated sugar consumption rates that cause a high substrate conversion to ethanol and other bi-products, severely affecting cell physiology, bioprocess performance, and biomass yields. Fed-batch culture, where sucrose consumption rates are controlled by the external addition of sugar aiming at its low concentrations in the fermentor, is the classical bioprocessing alternative to prevent sugar fermentation by yeasts. However, fed-batch fermentations present drawbacks that could be overcome by simpler batch cultures at relatively high (e.g. 20 g/L) initial sugar concentrations. In this study, a S. cerevisiae strain lacking invertase activity was engineered to transport sucrose into the cells through a low-affinity and low-capacity sucrose-H + symport activity, and the growth kinetics and biomass yields on sucrose analyzed using simple batch cultures.

Significance and Impact of Study: The Saccharomyces pastorianus lager yeast usually ferments maltose and maltotriose efficiently, and transport of these a-glucosides into the brewer's yeast cell is thought to be rate limiting in the fermentation of these sugars from wort. Our results revealed a new maltotriose transporter gene in the Saccharomyces eubayanus subgenome of the industrial lager brewing strain Weihenstephan 34/70 that allows efficient maltotriose fermentation by yeast cells. The characterization of maltotriose transporters from industrial yeasts opens new opportunities to increase yeast fitness for fermentation of brewer's wort, preventing incomplete or sluggish maltotriose fermentations. AbstractThe genome from the Saccharomyces pastorianus industrial lager brewing strain Weihenstephan 34/70, a natural Saccharomyces cerevisiae/Saccharomyces eubayanus hybrid, indicated the presence of two different maltotriose transporter genes: a new gene in the S. eubayanus subgenome with 81% of homology to the AGT1 permease from S. cerevisiae, and an amplification of the S. eubayanus MTY1 maltotriose permease previously identified in S. pastorianus yeasts. To characterize these S. eubayanus transporter genes, we used a S. cerevisiae strain deleted in the AGT1 permease and introduced the desired permease gene(s) into this locus through homologous recombination. Our results indicate that both the MTY1 and AGT1 genes from the S. eubayanus subgenome encode functional maltotriose transporters that allow fermentation of this sugar by yeast cells, despite their apparent differences in the kinetics of maltotriose-H + symport activity. The presence of two maltotriose transporters in the S. eubayanus subgenome not only highlights the importance of sugar transport for efficient maltotriose utilization by industrial yeasts, but these new genes can be used in breeding and/or selection programs aimed at increasing yeast fitness for the efficient fermentation of brewer's wort.

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Mangroves are ecosystems with unique characteristics due to the high salinity and amount of organic matter that house a rich biodiversity. Fungi have aroused much interest as they are an important natural source for the discovery of new bioactive compounds, with potential biotechnological and pharmacological interest. This review aims to highlight endophytic fungi isolated from mangrove plant species and the isolated bioactive compounds and their bioactivity against protozoa, bacteria and pathogenic viruses. Knowledge about this type of ecosystem is of great relevance for its preservation and as a source of new molecules for the control of pathogens that may be of importance for human, animal and environmental health.