Parental Yeast Research Articles

Enhancement of urea uptake in Chinese rice wine yeast strain N85 by the constitutive expression ofDUR3for ethyl carbamate elimination

Most of the fermented alcoholic beverages, particularly Chinese rice wine, contain the potentially human carcinogenic compound ethyl carbamate (EC). As a major EC precursor in Chinese rice wine, urea in fermentations can be transported into the yeast cell by urea permease and finally metabolized by urea carboxylase and allophanate hydrolase in vivo. To eliminate EC in Chinese rice wines, the present study constructed high urea uptake yeast strains N1-D, N2-D and N-D, by introducing a strong promoter (PGK1p) into the urea permease gene (DUR3) of the industrial Chinese rice wine yeast N85, and by the restoration of the URA3 gene at the same time. With these self-cloned, high urea uptake strains, the urea and EC in the terminal Chinese rice wine samples were reduced to different extents. With two copies of overexpressed DUR3, the N-D strain could reduce the urea and the EC by 53.4 and 26.1%, respectively. No difference in fermentation characteristics was found between the engineered strains and the parental industrial yeast strain N85. These results could help to optimize the genetic manipulation strategy for EC elimination in Chinese rice wine production. Copyright © 2015 The Institute of Brewing & Distilling

Evolution and genetic architecture of chromatin accessibility and function in yeast.

Chromatin accessibility is an important functional genomics phenotype that influences transcription factor binding and gene expression. Genome-scale technologies allow chromatin accessibility to be mapped with high-resolution, facilitating detailed analyses into the genetic architecture and evolution of chromatin structure within and between species. We performed Formaldehyde-Assisted Isolation of Regulatory Elements sequencing (FAIRE-Seq) to map chromatin accessibility in two parental haploid yeast species, Saccharomyces cerevisiae and Saccharomyces paradoxus and their diploid hybrid. We show that although broad-scale characteristics of the chromatin landscape are well conserved between these species, accessibility is significantly different for 947 regions upstream of genes that are enriched for GO terms such as intracellular transport and protein localization exhibit. We also develop new statistical methods to investigate the genetic architecture of variation in chromatin accessibility between species, and find that cis effects are more common and of greater magnitude than trans effects. Interestingly, we find that cis and trans effects at individual genes are often negatively correlated, suggesting widespread compensatory evolution to stabilize levels of chromatin accessibility. Finally, we demonstrate that the relationship between chromatin accessibility and gene expression levels is complex, and a significant proportion of differences in chromatin accessibility might be functionally benign.

Decreased ethyl carbamate generation during Chinese rice wine fermentation by disruption of CAR1 in an industrial yeast strain

Saccharomyces cerevisiae metabolizes arginine to ornithine and urea during wine fermentations. In the fermentation of Chinese rice wine, yeast strains of S. cerevisiae do not fully metabolize urea, which will be secreted into the spirits and spontaneously reacts with ethanol to form ethyl carbamate, a potential carcinogenic agent for humans. To block the pathway of urea production, we genetically engineered two haploid strains to reduce the arginase (encoded by CAR1) activity, which were isolated from a diploid industrial Chinese rice wine strain. Finally the engineered haploids with opposite mating type were mated back to diploid strains, obtaining a heterozygous deletion strain (CAR1/car1) and a homozygous defect strain (car1/car1). These strains were compared to the parental industrial yeast strain in Chinese rice wine fermentations and spirit production. The strain with the homozygous CAR1 deletion showed significant reductions of urea and EC in the final spirits in comparison to the parental strain, with the concentration reductions by 86.9% and 50.5% respectively. In addition, EC accumulation was in a much lower tempo during rice wine storage. Moreover, the growth behavior and fermentation characteristics of the engineered diploid strain were similar to the parental strain.

Extensive heterosis in growth of yeast hybrids is explained by a combination of genetic models.

Heterosis, also known as hybrid vigor, is the superior performance of a heterozygous hybrid relative to its homozygous parents. Despite the scientific curiosity of this phenotypic phenomenon and its significance for food production in agriculture, its genetic basis is insufficiently understood. Studying heterosis in yeast can potentially yield insights into its genetic basis, can allow one to test the different hypotheses that have been proposed to explain the phenomenon and allows better understanding of how to take advantage of this phenomenon to enhance food production. We therefore crossed 16 parental yeast strains to form 120 yeast hybrids, and measured their growth rates under five environmental conditions. A considerable amount of dominant genetic variation was found in growth performance, and heterosis was measured in 35% of the hybrid-condition combinations. Despite previous reports of correlations between heterosis and measures of sequence divergence between parents, we detected no such relationship. We used several analyses to examine which genetic model might explain heterosis. We found that dominance complementation of recessive alleles, overdominant interactions within loci and epistatic interactions among loci each contribute to heterosis. We concluded that in yeast heterosis is a complex phenotype created by the combined contribution of different genetic interactions.

Evidence for the role of wheat eukaryotic translation initiation factor 3 subunit g (TaeIF3g) in abiotic stress tolerance

The gene encoding eIF3g (TaeIF3g), one of the 11 subunits of eukaryotic translation initiation factor 3 (eIF3), was cloned from wheat for carrying out its functional analysis. Transgenic expression of TaeIF3g enhanced the tolerance of TaeIF3g-overexpressing parental yeast cells and Arabidopsis plants under different abiotic stress conditions. Compared to untransformed plants, TaeIF3g-overexpressing Arabidopsis thaliana plants exhibited significantly higher survival rate, soluble proteins and photosynthetic efficiency, and enhanced protection against photooxidative stress under drought conditions. This study provides first evidence that TaeIF3g imparts stress tolerance and could be a potential candidate gene for developing crop plants tolerant to abiotic stress.

QTL Analysis of High Thermotolerance with Superior and Downgraded Parental Yeast Strains Reveals New Minor QTLs and Converges on Novel Causative Alleles Involved in RNA Processing

Revealing QTLs with a minor effect in complex traits remains difficult. Initial strategies had limited success because of interference by major QTLs and epistasis. New strategies focused on eliminating major QTLs in subsequent mapping experiments. Since genetic analysis of superior segregants from natural diploid strains usually also reveals QTLs linked to the inferior parent, we have extended this strategy for minor QTL identification by eliminating QTLs in both parent strains and repeating the QTL mapping with pooled-segregant whole-genome sequence analysis. We first mapped multiple QTLs responsible for high thermotolerance in a natural yeast strain, MUCL28177, compared to the laboratory strain, BY4742. Using single and bulk reciprocal hemizygosity analysis we identified MKT1 and PRP42 as causative genes in QTLs linked to the superior and inferior parent, respectively. We subsequently downgraded both parents by replacing their superior allele with the inferior allele of the other parent. QTL mapping using pooled-segregant whole-genome sequence analysis with the segregants from the cross of the downgraded parents, revealed several new QTLs. We validated the two most-strongly linked new QTLs by identifying NCS2 and SMD2 as causative genes linked to the superior downgraded parent and we found an allele-specific epistatic interaction between PRP42 and SMD2. Interestingly, the related function of PRP42 and SMD2 suggests an important role for RNA processing in high thermotolerance and underscores the relevance of analyzing minor QTLs. Our results show that identification of minor QTLs involved in complex traits can be successfully accomplished by crossing parent strains that have both been downgraded for a single QTL. This novel approach has the advantage of maintaining all relevant genetic diversity as well as enough phenotypic difference between the parent strains for the trait-of-interest and thus maximizes the chances of successfully identifying additional minor QTLs that are relevant for the phenotypic difference between the original parents.

Disruption of the MIG1 gene enhances lipid biosynthesis in the oleaginous yeast Yarrowia lipolytica ACA-DC 50109

In this study, the MIG1 gene in the oleaginous yeast Yarrowia lipolytica ACA-DC 50109 (the parent yeast) was disrupted and the disruptant M25 obtained could grow in yeast nitrogen base-N5000 medium without uracil or the medium with 2-deoxy-D-glucose. It was found that the cells of the disruptant M25 had more lipid bodies than those of its parent yeast. The disruptant M25 contained 48.7% (w/w) of oil based on its cell weight while the parent yeast only contained 36.0% (w/w) of oil. Transcript levels of many genes relevant to lipid biosynthesis in the disruptant M25 were enhanced compared to those of the same genes in the parent yeast. However, transcript level of the MFE1 gene, one of the genes relevant to fatty acid degradation was reduced in the disruptant M25 compared to that of the same gene in the parent yeast. Such changes in gene expression profile may cause the increased lipid biosynthesis in the disruptant M25. Biosynthesis of C18:1 fatty acid in the disruptant M25 was greatly enhanced compared to that in the parent yeast.

Proteomic Research Reveals the Stress Response and Detoxification of Yeast to Combined Inhibitors

The tolerant mechanism of yeast to the combination of three inhibitors (furfural, phenol and acetic acid) was investigated using 2-DE combined with MALDI-TOF/TOF-MS. The stress response and detoxification related proteins (e.g., Ahp1p, Hsp26p) were expressed higher in the tolerant yeast than in the parental yeast. The expressions of most nitrogen metabolism related proteins (e.g. Gdh1p, Met1p) were higher in the parental yeast, indicating that the tolerant yeast decreases its nitrogen metabolism rate to reserve energy, and possesses high resistance to the stress of combined inhibitors. Furthermore, upon exposure to the inhibitors, the proteins related to protein folding, degradation and translation (e.g., Ssc1p, Ubp14p, Efb1p) were all significantly affected, and the oxidative stress related proteins (e.g., Ahp1p, Grx1p) were increased. Knockdown of genes related to the oxidative stress and unfolded protein response (Grx1, Gre2, Asc1) significantly decreased the tolerance of yeast to inhibitors, which further suggested that yeast responded to the inhibitors mainly by inducing unfolded protein response. This study reveals that increasing the detoxification and tolerating oxidative stress, and/or decreasing the nitrogen metabolism would be promising strategies in developing more tolerant strains to the multiple inhibitors in lignocellulose hydrolysates.

Pilot-scale evaluation the enological traits of a novel, aromatic wine yeast strain obtained by adaptive evolution

In the competitive context of the wine market, there is a growing interest for novel wine yeast strains that have an overall good fermentation capacity and that contribute favorably to the organoleptic quality of wine. Using an adaptive evolution strategy based on growth on gluconate as sole carbon source, we recently obtained wine yeasts with improved characteristics in laboratory-scale fermentations. The characteristics included enhanced fermentation rate, decreased formation of acetate and greater production of fermentative aroma. We report an evaluation of the potential value of the evolved strain ECA5™ for winemaking, by comparing its fermentation performance and metabolite production to those of the parental strain in pilot-scale fermentation trials, with various grape cultivars and winemaking conditions. We show that the evolved strain has outstanding attributes relative to the parental wine yeast strain, and in particular the production of less volatile acidity and greater production of desirable volatile esters, important for the fruity/flowery character of wines. This study highlights the potential of evolutionary engineering for the generation of strains with a broad range of novel properties, appropriate for rapid application in the wine industry.

Association of deoxyhypusine hydroxylase with peroxiredoxin I was modulated in the yeast Saccharomyces cerevisiae under oxidative stress

Eukaryotic translation initiation factor 5A (eIF5A) is the only hypusine-containing protein, which is formed by deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH). DOHH is a novel metalloenzyme with HEAT [named for human huntingtin (H), elongation factor 3 (E), a subunit of protein phosphatase 2A (A), and the target of rapamycin (T)]-repeat motifs. Inspite of much progress in determining the roles of iron-containing DOHH holoenzyme as an eIF5A hydroxylase, little is known about iron-free apoenzyme of DOHH under certain stress conditions. For this purpose, we compared cell growth in two yeast strains subjected to oxidative damage. Thus, the existence of more viable cells in the Saccharomyces cerevisiae BY4743 (parental yeast) strain than in the DOHH-null strain after H2O2 treatment indicates the importance of DOHH in protecting yeast cells against oxidative stress. To identify endogenous target proteins influenced by DOHH under oxidative damage, proteomic analysis was applied to the two yeast strains. Of these proteins, the oxidized form of peroxiredoxin I (PrxI) was concomitantly up-regulated in both strains under H2O2 treatment. Two-dimensional electrophoresis (DE) followed by immunoblot analysis shows that the recovery of the oxidized PrxI to the reduced enzyme under H2O2 treatment was found to be much slower in the DOHH-null strain than in the parental strain. Based on the results, we discovered a possible interaction between DOHH and PrxI by immunoprecipitation/ immunoblotting in yeast under oxidative stress. Taken together, these results suggest that DOHH might be a candidate protein for protection of yeast cells against oxidative stress in conjunction with PrxI.

Comparative metabolic profiling of parental and inhibitors-tolerant yeasts during lignocellulosic ethanol fermentation

The metabolic responses of parental and inhibitors-tolerant yeasts in presence of the combination of three inhibitors (furfural, phenol and acetic acid) during ethanol fermentation were investigated by comparative metabolic profiling. Samples of parental and tolerant yeasts with/without three inhibitors in fermentation medium represented significantly different metabolic states. Further investigation on the specific responses of two strains revealed that the levels of most amino acids, inositol, and phenethylamine were dramatically increased in presence of inhibitors in parental yeast, while they kept relatively stable in tolerant yeast. It suggested that the protein degradation was increased and oxygen stress was induced by combined inhibitors in parental yeast. In addition, carbon metabolism (glycolysis and TCA) and pyrimidine ribonucleotides pathway (uracil and cytosine) were reduced in both strains in presence of combined inhibitors, which was considered as the general stress response. Higher levels of pyridimines in tolerant yeast suggested that they were responsible for counteracting the stress of combined inhibitors. These findings provided new insights into underlying mechanisms of yeast in resistance to the synergistic effects of inhibitors in lignocellulose hydrolysates.

Genetic control of protein and glucose-anabolic-enzyme syntheses by <i>Saccharomyces cerevisiae</i> in the fermentation of a Nigerian rice, <i>Oryza sativa</i> variety “Igbimo”

This work aimed at the control of the production of protein and glucose-anabolic-enzyme (GAE) by Saccharomyces cerevisiae during the fermentation of a Nigerian rice, Oryza sativa variety “Igbimo”. The yeast was mutated with ethylmethyl sulphonate. The variants and the parental yeast were separately inoculated into cooked rice and allowed to ferment at 27℃ for 7 days after which protein content and glucose-anabolic-enzyme synthesis were determined using Dinitrosalicylic acid and Biuret reagents techniques. Mutants with varying capacities to form protein and GAE were obtained. Glucose-Anabolic-Enzyme (GAE) activity ranged from 0.25 to 12.06 Units forming five groups (classes 1, 2, 3, 4 and 5) with the average activity of 0.52, 1.52, 2.28, 4.04 and 10.63 Units respectively compared with that (0.38 Unit) of the parent strain. All the mutants synthesized protein although many of them produced it at lower level while others at higher level than the wild-type. The highest (5.92 mg/mL) and lowest (0.10 mg/mL) levels protein producers are mutants 44 and 14 respectively. Mutants No. 4, 7, 22 and 78 formed total protein similar in concentrations (1.46, 1.46, 1.45 and 1.45 mg/mL) to that of the wild yeast (1.46 mg/mL). These three sets of protein concentration have ratios 4.1 (highest), 0.07 (lowest) and 1.0 (normal) to that of the parental yeast.

Pnc1p Supports Increases in Cellular NAD(H) Levels in Response to Internal or External Oxidative Stress

Following transfer from medium with fermentable glucose to medium with nonfermentable acetate as the carbon source, cellular levels of NAD(H) were found to increase approximately 2-fold in a parental yeast strain. Similar transfer of a mutant strain subject to endogenous oxidative stress under these conditions produced more dramatic increases in cellular levels of NAD(H), and elevations above parental levels were shown to be due to the nicotinimidase Pnc1p. Similar transient increases in NAD(H) levels observed in the parental strain following addition of exogenous hydrogen peroxide were also attributable to Pnc1p.

High Expression Levels of Cell Wall Protein Cwp2p Decrease the Turbidity of Fresh Lager Beer by Reducing the Size of Haze Particles

Cwp2p is one of the major mannoproteins of the yeast cell wall. In this study, the CWP2 gene was placed under the constitutive TDH3 promoter and introduced into a lager production strain. When the obtained CWP2-enhanced strain was subjected to a fermentation trial, the resultant beer was less turbid and contained haze particles that were smaller than those in the control beer with the parental strain. Enhanced expression of CWP2 in the transformant strain resulted in a reduction in the size of haze particles, similar to a case in which the parental strain was propagated aerobically for the fermentation trial. The aerobically prepared parental pitching yeast cells exhibited a higher level of CWP2 mRNA expression during fermentation. These results suggest that the aerobic propagation of pitching yeast exerts a haze-reduction effect by changing the expression profiles of specific cell wall mannoproteins, including Cwp2p. Immunoblot analysis detected the green fluorescent protein-cell wall protein (GFP-Cwp2p) fusion protein in fresh beer when expressed in a lager brewing strain, indicating that a glycosylphosphatidylinositol (GPI)-anchored cell wall protein, such as Cwp2p, can be released into a solution under physiological conditions. The expression level of the aerobiosis-specific mannoproteins (e.g., Cwp2p) appeared to be a key factor in the determination of haze particle size and, accordingly, beer turbidity.

Redox responses in yeast to acetate as the carbon source

Following a shift to medium with acetate as the carbon source, a parental yeast strain exhibited a transient moderate 20% reduction in total cellular [NAD + + NADH] but showed a ∼10-fold increase in the ratio of [NAD +]:[NADH] after 36 h. A mutant strain ( idhΔ) lacking the tricarboxylic acid cycle enzyme isocitrate dehydrogenase had 50% higher cellular levels of [NAD + + NADH] relative to the parental strain but exhibited similar changes in cofactor concentrations following a shift to acetate medium, despite an inability to grow on that carbon source; essentially all of the cofactor was in the oxidized form within 36 h. The salvage pathway for NAD(H) biosynthesis was found to be particularly important for viability during early transition of the parental strain to stationary phase in acetate medium. However, oxygen consumption was not affected, suggesting that the NAD(H) produced during this time may support other cellular functions. The idhΔ mutant exhibited increased flux through the salvage pathway in acetate medium but was dependent on the de novo pathway for viability. Long-term chronological lifespans of the parental and idhΔ strains were similar, but viability of the mutant strain was dependent on both pathways for NAD(H) biosynthesis.

Switching the mode of sucrose utilization by Saccharomyces cerevisiae

BackgroundOverflow 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.ResultsWe have deleted from the genome of a S. cerevisiae strain lacking invertase the high-affinity sucrose-H+ symporter encoded by the AGT1 gene. This strain could still grow efficiently on sucrose due to a low-affinity and low-capacity sucrose-H+ symport activity mediated by the MALx1 maltose permeases, and its further intracellular hydrolysis by cytoplasmic maltases. Although sucrose consumption by this engineered yeast strain was slower than with the parental yeast strain, the cells grew efficiently on sucrose due to an increased respiration of the carbon source. Consequently, this engineered yeast strain produced less ethanol and 1.5 to 2 times more biomass when cultivated in simple batch mode using 20 g/L sucrose as the carbon source.ConclusionHigher cell densities during batch cultures on 20 g/L sucrose were achieved by using a S. cerevisiae strain engineered in the sucrose uptake system. Such result was accomplished by effectively reducing sucrose uptake by the yeast cells, avoiding overflow metabolism, with the concomitant reduction in ethanol production. The use of this modified yeast strain in simpler batch culture mode can be a viable option to more complicated traditional sucrose-limited fed-batch cultures for biomass-directed processes of S. cerevisiae.

Rev1 and Polζ influence toxicity and mutagenicity of Me-lex, a sequence selective N3-adenine methylating agent

The relative toxicity and mutagenicity of Me-lex, which selectively generates 3-methyladenine (3-MeA), is dependent on the nature of the DNA repair background. Base excision repair (BER)-defective S. cerevisiae strains mag1 and apn1apn2 were both significantly more sensitive to Me-lex toxicity, but only the latter is significantly more prone to Me-lex-induced mutagenesis. To examine the contribution of translesion synthesis (TLS) DNA polymerases in the bypass of Me-lex-induced lesions, the REV3 and REV1 genes were independently deleted in the parental yeast strain and in different DNA repair-deficient derivatives: the nucleotide excision repair (NER)-deficient rad14, and the BER-deficient mag1 or apn1apn2 strains. The strains contained an integrated ADE2 reporter gene under control of the transcription factor p53. A centromeric yeast expression vector containing the wild-type p53 cDNA was treated in vitro with increasing concentrations of Me-lex and transformed into the different yeast strains. The toxicity of Me-lex-induced lesions was evaluated based on the plasmid transformation efficiency compared to the untreated vector, while Me-lex mutagenicity was assessed using the p53 reporter assay. In the present study, we demonstrate that disruption of Polζ (through deletion of its catalytic subunit coded by REV3) or Rev1 (by REV1 deletion) increased Me-lex lethality and decreased Me-lex mutagenicity in both the NER-defective ( rad14) and BER-defective ( mag1; apn1apn2) strains. Therefore, Polζ and Rev1 contribute to resistance of the lethal effects of Me-lex-induced lesions (3-MeA and derived AP sites) by bypassing lesions and fixing some mutations.

Azole antifungals induce up-regulation of SAP4, SAP5 and SAP6 secreted proteinase genes in filamentous Candida albicans cells in vitro and in vivo

Expression of fungal virulence factors can be influenced by exposure to antifungal agents. To test this hypothesis, we determined the effects of subinhibitory concentrations of three antifungal agents on expression of three secreted proteinase genes associated with virulence in filamentous forms of Candida albicans. GFP-SAP promoter constructs and fluorescence measurement, transcript profiling and RT-PCR in vitro and in an animal model of disseminated Candida infection. Exposure of C. albicans to subinhibitory concentrations of fluconazole in RPMI 1640 in the absence of serum led to up-regulation of the virulence-associated genes SAP4, SAP5 and SAP6 in hyphae and long pseudohyphae. Measurements with green fluorescent protein (GFP)-tagged promoters showed that the fluorescence of SAP4 and SAP6 under these conditions was strongest in the apical tip compartments of these filamentous cells and declined in compartments more proximal to the parent yeast cell. By contrast, SAP5-GFP fluorescence was expressed at similar levels in all cell compartments. Exposure to fluconazole led to significant increases in GFP-SAP4 and -SAP6 fluorescence in the filaments; itraconazole exposure also significantly increased GFP-SAP4 fluorescence, whereas flucytosine had no effect on any of the constructs. In experimentally infected animals, fluorescence of the GFP-SAP promoter fungal cells in kidney tissues was greater than that was seen in vitro for all four SAP constructs: treatment of animals with fluconazole did not significantly increase SAP promoter expression as measured by GFP fluorescence. Azole antifungal agents stimulated up-regulation of SAP4 and SAP6 genes in filamentous C. albicans cells in vitro and may therefore influence virulence as well as growth of the fungus. However, such effects appear to be transient in vivo.

Functional Analyses of the Malolactic Wine Yeast ML01

Deacidification of grape musts and wines is important for the production of well-balanced wines. The bacterial malolactic fermentation (MLF) process is unreliable and stuck MLF often leads to spoilage of wines and the production of biogenic amines. The genetically engineered wine yeast, ML01, is a Prise de Mousse strain that contains the malate transport gene (<i>mae1</i>) from <i>Schizosaccharomyces pombe</i> and the malolactic gene (<i>mleA</i>) from <i>Oenococcus oeni</i>, stably integrated into the genome at the <i>URA3</i> locus. Both genes were isolated from wine-related microorganisms and are expressed under control of the <i>Saccharomyces cerevisiae PGK1</i> promoter and terminator sequences. ML01 is capable of decarboxylating up to 9.2 g/L of malate to equimolar amounts of lactate in Chardonnay grape must during the alcoholic fermentation. ML01 contains no antibiotic resistance marker genes or vector DNA sequences. The presence of the malolactic cassette in the genome does not affect growth, ethanol production, fermentation kinetics, or metabolism of ML01. Wines produced by the ML01 yeast have lower volatile acidity and improved color properties than wines produced with the parental yeast and a bacterial MLF. Analysis of the volatile compounds, sensory analyses, and industrial production of wine indicate that ML01 is suitable for the commercial production of quality wine.

Disruption of Brewer's Yeast Alcohol Dehydrogenase II Gene and Reduction of Acetaldehyde Content during Brewery Fermentation

In an attempt to reduce acetaldehyde content in the final beer product, mutant strains of brewer's yeasts were constructed by genetic homologous recombination, in which the alcohol dehydrogenase II (ADHII) gene was partially disrupted. The strains were tested on the scale of 100 L of pilot fermentation. Compared with that of the parent yeast, the results showed an obvious decline of acetaldehyde content with mutant yeast at the end of fermentation, especially when fermentable sugar was depleted. The final acetaldehyde content of beer obtained with parent and mutant yeasts was 7.82 and 2.54 mg/L, respectively. However, no evident differences in brewing performance, such as the ability to utilize sugar, growing, and flocculating, were revealed between parent and mutant yeasts. Additionally, no clear differences were found between parent and mutant yeasts in the production of other volatile compounds and sensory analysis of attributes. Therefore, these approaches uncover the possibility of reducing and controlling acetaldehyde content during beer production.