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Meiotic crossovers are initiated from programmed DNA double-strand breaks. The Msh4–Msh5 heterodimer is an evolutionarily conserved mismatch repair–related protein complex that promotes meiotic crossovers by stabilizing strand invasion intermediates and joint molecule structures such as Holliday junctions. In vivo studies using homozygous strains of the baker's yeast Saccharomyces cerevisiae (SK1) show that the Msh4–Msh5 complex associates with double-strand break hotspots, chromosome axes, and centromeres. Many organisms have heterozygous genomes that can affect the stability of strand invasion intermediates through heteroduplex rejection of mismatch-containing sequences. To examine Msh4–Msh5 function in a heterozygous context, we performed chromatin immunoprecipitation and sequencing (ChIP-seq) analysis in a rapidly sporulating hybrid S. cerevisiae strain (S288c-sp/YJM789, containing sporulation-enhancing QTLs from SK1), using SNP information to distinguish reads from homologous chromosomes. Overall, Msh5 localization in this hybrid strain was similar to that determined in the homozygous strain (SK1). However, relative Msh5 levels were reduced in regions of high heterozygosity, suggesting that high mismatch densities reduce levels of recombination intermediates to which Msh4–Msh5 binds. Msh5 peaks were also wider in the hybrid background compared to the homozygous strain (SK1). We determined regions containing heteroduplex DNA by detecting chimeric sequence reads with SNPs from both parents. Msh5 -bound double-strand break hotspots overlap with regions that have chimeric DNA, consistent with Msh5 binding to heteroduplex-containing recombination intermediates. [ABSTRACT FROM AUTHOR]

Aim: This study is to investigate the use of a constitutively expressed trehalose transport protein to directly control intracellular trehalose levels and protect baker's yeast (Saccharomyces cerevisiae) cells against freeze–thaw stress in vivo. Methods and Results: We used a constitutively overexpressed Agt1 transporter to investigate the role of trehalose in the freeze–thaw tolerance of yeast cells by regulating intracellular trehalose concentrations independently of intracellular biosynthesis. Using this method, we found that increasing intracellular trehalose in yeast cells improved cell survival rate after 8 days of freezing at −80 and −20°C. We also observed that freeze–thaw tolerance promoted by intracellular trehalose only occurs in highly concentrated cell pellets rather than cells in liquid suspension. Conclusions: Trehalose is sufficient to provide freeze–thaw tolerance using our Agt1 overexpression system. Freeze–thaw tolerance can be further enhanced by deletion of genes encoding intracellular trehalose degradation enzymes. Significance and Impact of Study: These findings are relevant to improving the freeze–thaw tolerance of baker's yeast in the frozen baked goods industry through engineering strains that can accumulate intracellular trehalose via a constitutively expressed trehalose transporter and inclusion of trehalose into the growth medium. [ABSTRACT FROM AUTHOR]

Yeast autolysis refers to the process in which cells degrade and release intracellular contents under specific conditions by endogenous enzymes such as proteases, nucleases and lipid enzymes. Protein-rich baker's yeast is widely used to produce yeast extract in food industry, however, the molecular mechanism related to baker's yeast autolysis is still unclear. In this study, RNA-seq technology and biochemical analysis were performed to analyze the autolysis processes in baker's yeast. The differentially expressed genes (DEGs), 27 autolysis-related euKaryotic Ortholog Groups (KOG) and three types of autolysis-induced Gene Ontology (GO) were identified and analyzed in detail. A total of 143 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways under autolysis were also assigned. Interestingly, the DEGs were significantly enriched in the mitogen-activated protein kinase (MAPK) signaling pathways and metabolic pathways, and key genes MID2 , MTL1 , SLT2 , PTP2 , HKR1 and GPD1 may play important roles in autolysis. Further quantitative PCR was performed to verify the expression pattern in baker's yeast autolysis. Together, all these results indicated that MAPK pathways might play an essential role during autolysis process through inhibiting the metabolism and disrupting cell wall in baker's yeast. This result may provide important clues for the in-depth interpretation of the yeast autolysis mechanism. [ABSTRACT FROM AUTHOR]

Maltose metabolism of baker’s yeast (Saccharomyces cerevisiae) in lean dough is suppressed by the glucose effect, which negatively affects dough fermentation. In this study, differences and interactions among SNF4 (encoding for the regulatory subunit of Snf1 kinase) overexpression and REG1 and REG2 (which encodes for the regulatory subunits of the type I protein phosphatase) deletions in maltose metabolism of baker’s yeast were investigated using various mutants. Results revealed that SNF4 overexpression and REG1 and REG2 deletions effectively alleviated glucose repression at different levels, thereby enhancing maltose metabolism and leavening ability to varying degrees. SNF4 overexpression combined with REG1/REG2 deletions further enhanced the increases in glucose derepression and maltose metabolism. The overexpressed SNF4 with deleted REG1 and REG2 mutant ΔREG1ΔREG2 + SNF4 displayed the highest maltose metabolism and strongest leavening ability under the test conditions. Such baker’s yeast strains had excellent potential applications. [ABSTRACT FROM AUTHOR]

Baker's yeast strains with freeze-tolerance are highly desirable to maintain high leavening ability after freezing. Enhanced intracellular concentration of trehalose and proline in yeast is linked with freeze-tolerance. In this study, we constructed baker's yeast with enhanced freeze-tolerance by simultaneous deletion of the neutral trehalase-encoded gene NTH1 and the proline oxidase-encoded gene PUT1. We first used the two-step integration-based seamless gene deletion method to separately delete NTH1 and PUT1 in haploid yeast. Subsequently, through two rounds of hybridization and sporulation-based allelic exchange and colony PCR-mediated tetrad analysis, we obtained strains with restored URA3 and deletion of NTH1 and/or PUT1. The resulting strain showed higher cell survival and dough-leavening ability after freezing compared to the wild-type strain due to enhanced accumulation of trehalose and/or proline. Moreover, mutant with simultaneous deletion of NTH1 and PUT1 exhibits the highest relative dough-leavening ability after freezing compared to mutants with single-gene deletion perhaps due to elevated levels of both trehalose and proline. These results verified that it is applicable to construct frozen dough baker's yeast using the method proposed in this paper. [ABSTRACT FROM AUTHOR]

Dough-leavening ability is one of the main aspects considered when selecting a baker's yeast strain for baking industry. Generally, modification of maltose metabolic pathway and known regulatory networks of maltose metabolism were used to increase maltose metabolism to improve leavening ability in lean dough. In this study, we focus on the effects of PGM2 (encoding for the phosphoglucomutase) and SNR84 (encoding for the H/ACA snoRNA) that are not directly related to both the maltose metabolic pathway and known regulatory networks of maltose metabolism on the leavening ability of baker's yeast in lean dough. The results show that the modifications on PGM2 and/or SNR84 are effective ways in improving leavening ability of baker's yeast in lean dough. Deletion of PGM2 decreased cellular glucose-1-phosphate and overexpression of SNR84 increased the maltose permease activity. These changes resulted in 11, 19 and 21 % increases of the leavening ability for PGM2 deletion, SNR84 overexpression and SNR84 overexpression combining deleted PGM2, respectively. [ABSTRACT FROM AUTHOR]

Several recombinant strains with overexpressed trehalose-6-phosphate synthase gene ( TPS1) and/or deleted trehalase genes were obtained to elucidate the relationships between TPS1, trehalase genes, content of intracellular trehalose and freeze tolerance of baker's yeast, as well as improve the fermentation properties of lean dough after freezing. In this study, strain TL301 overexpressing TPS1 showed 62.92 % higher trehalose-6-phosphate synthase (Tps1) activity and enhanced the content of intracellular trehalose than the parental strain. Deleting ATH1 exerted a significant effect on trehalase activities and the degradation amount of intracellular trehalose during the first 30 min of prefermentation. This finding indicates that acid trehalase (Ath1) plays a role in intracellular trehalose degradation. NTH2 encodes a functional neutral trehalase (Nth2) that was significantly involved in intracellular trehalose degradation in the absence of the NTH1 and/or ATH1 gene. The survival ratio, freeze-tolerance ratio and relative fermentation ability of strain TL301 were approximately twice as high as those of the parental strain (BY6-9α). The increase in freeze tolerance of strain TL301 was accompanied by relatively low trehalase activity, high Tps1 activity and high residual content of intracellular trehalose. Our results suggest that overexpressing TPS1 and deleting trehalase genes are sufficient to improve the freeze tolerance of baker's yeast in frozen dough. The present study provides guidance for the commercial baking industry as well as the research on the intracellular trehalose mobilization and freeze tolerance of baker's yeast. [ABSTRACT FROM AUTHOR]

This study aimed to increase maltose fermentation in industrial baker's yeast to increase its leavening properties. To this end, we overexpressed MAL62 encoding alpha-glucosidase (maltase) and deleted MIG1 encoding a transcriptional repressor that regulates MAL gene expression. Strain overexpressing MAL62 showed 46.3 % higher alpha-glucosidase activity and enhanced leaving activity than the parental strain when tested in glucose-maltose low sugar model liquid dough (LSMLD). Deleting MIG1 was much less effective, but it could further strengthen leavening properties in a strain overexpressing MAL62. The relationship between maltose permease and alpha-glucosidase was further dissected by transforming the two genes. The results indicated that without increasing the maltose permease activity, maltose metabolism could also be enhanced by the increased alpha-glucosidase activity. Previous strategies for strain improvement have targeted the enhancement of alpha-glucosidase and maltose permease activities in concert. Our results suggest that increasing alpha-glucosidase activity is sufficient to improve maltose fermentation in lean dough. [ABSTRACT FROM AUTHOR]

The article discusses enhancement in the fermentation capability of industrial baker's yeast by overexpression of the transcription activator Msn2 in frozen dough. The cloned yeast was found to have higher tolerance to freeze thaw stress with higher intracellular trehalose level when compared with the wild type strain. The desired feature of cloned yeast which provides protection to various cellular components against freeze thaw stress including proteins, membrane lipids is also described.

Properties of 13 Saccharomyces cerevisiae strains isolated from different sources (traditional sourdoughs, industrial baking yeasts etc.) were studied in dough produced with durum wheat (Sicilian semolina, variety Mongibello). Durum wheat semolina and durum wheat flour are products prepared from grain of durum wheat (Triticum durum Desf.) by grinding or milling processes in which the bran and germ are essentially removed and the remainder is comminuted to a suitable degree of fineness. Acidification and leavening properties of the dough were evaluated. Strains isolated from traditional sourdoughs (DSM PST18864, DSM PST18865 and DSM PST18866) showed higher leavening power, valuable after the first and second hours of fermentation, than commercial baking yeasts. In particular the strain DSM PST 18865 has also been successfully tested in bakery companies for the improvement of production processes. Baking and staling tests were carried out on five yeast strains to evaluate their fermentation ability directly and their resistance to the staling process. Amplified fragment length polymorphism (fAFLP) was used to investigate genetic variations in the yeast strains. This study showed an appreciable biodiversity in the microbial populations of both wild and commercial yeast strains. [ABSTRACT FROM AUTHOR]

The effect of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) on the asymmetric reduction of ethyl 2-oxo-4-phenylbutyrate (EOPB) to synthesize optical active ethyl 2-hydroxy-4-phenylbutyrate (EHPB) catalyzed by Saccharomyces cerevisiae was investigated. ( R)-EHPB [70.4%, e.e.( R)] is obtained using ethyl ether or benzene as the solvent. The main product is ( S)-EHPB [27.7%, e.e.( S)] in [BMIM][PF6]. However, in ionic liquid-water (10:1, v/v) biphasic system, the enantioselectivity of the reduction is shifted towards ( R)-side, and e.e.( R) is increased from 6.6 to 82.5% with the addition of ethanol (1%, v/v). The effect of the use of [BMIM][PF6] as an additive in relatively small amounts on the reduction was also studied. We find that there is a decline in the enantioselectivity of the reduction in benzene. In addition, a decrease in the conversion of EOPB and the yield of EHPB with increasing [BMIM][PF6] concentrations occurs in either organic solvent–water biphasic systems or benzene. [ABSTRACT FROM AUTHOR]

Aims: The aim of this investigation was to determine a better leavening ability and shelf life for the same biomass yield of final product. Methods and Results: A commercial fed-batch bioreactor equipped with circulation loop was used to study the effect of carbon source, molasses, profile on dough-leavening ability, shelf life and biomass yield of Baker’s yeast, Saccharomyces cerevisiae. A set of 32 commercial batches were performed to investigate the effect of sugar concentration and compare with 32 control experiments. Conclusions: Higher local sugar concentration in circulation loop resulted in a better leavening ability and shelf life for the same biomass yield of the final product. In addition, this method improved nitrogen assimilation which resulted in higher protein content. Increase in leavening ability and protein content could be a result of the higher levels of glycolytic enzymes. Significance and Impact of the Study: It was observed that this change resulted in considerable improvement in leavening ability and shelf life at a commercial scale. It must be emphasized that to improve product quality, it is not necessary to pursue classical mutagenesis and selection strategies. A high-quality product can be achieved only by optimizing the feeding profile and strategy. [ABSTRACT FROM AUTHOR]

N-Lauroyl sarcosine (LS), a cationic, non-toxic and biodegradable detergent readily permeabilized whole cells of baker’s yeast ( Saccharomyces cerevisiae). Permeabilization was carried out to increase assayable cellular catalase activity, an enzyme of great physiological and industrial importance, and to release 5′-nucleotides which find food/nutritional applications. The event of permeabilization was concentration, time and temperature dependent. Maximum permeabilization of yeast cells were observed when 1 g wet weight (0.2 g dry wt) of cells were permeabilized with 1.0 ml of 2% LS at 45 °C for 15 min. LS-permeabilized cells showed 350-fold increase in catalase activity and the supernatant obtained after permeabilization was rich in 5′-nucleotides. LS-permeabilized baker’s yeast cells can be used as a source of biocatalyst and to isolate valuable by-products. [ABSTRACT FROM AUTHOR]

Yeasts used in bread making are exposed to freeze–thaw stress during frozen-dough baking. To clarify the genes required for freeze–thaw tolerance, genome-wide screening was performed using the complete deletion strain collection of diploid Saccharomyces cerevisiae. The screening identified 58 gene deletions that conferred freeze–thaw sensitivity. These genes were then classified based on their cellular function and on the localization of their products. The results showed that the genes required for freeze–thaw tolerance were frequently involved in vacuole functions and cell wall biogenesis. The highest numbers of gene products were components of vacuolar H+-ATPase. Next, the cross-sensitivity of the freeze–thaw-sensitive mutants to oxidative stress and to cell wall stress was studied; both of these are environmental stresses closely related to freeze–thaw stress. The results showed that defects in the functions of vacuolar H+-ATPase conferred sensitivity to oxidative stress and to cell wall stress. In contrast, defects in gene products involved in cell wall assembly conferred sensitivity to cell wall stress but not to oxidative stress. Our results suggest the presence of at least two different mechanisms of freeze–thaw injury: oxidative stress generated during the freeze–thaw process, and defects in cell wall assembly. [ABSTRACT FROM AUTHOR]

Yeasts used in bread making are exposed to high concentrations of sucrose during sweet dough fermentation. Despite its importance, tolerance to high-sucrose stress is poorly understood at the gene level. To clarify the genes required for tolerance to high-sucrose stress, genome-wide screening was undertaken using the complete deletion strain collection of diploid Saccharomyces cerevisiae. The screening identified 273 deletions that yielded high sucrose sensitivity, approximately 20 of which were previously uncharacterized. These 273 deleted genes were classified based on their cellular function and localization of their gene products. Cross-sensitivity of the high-sucrose-sensitive mutants to high concentrations of NaCl and sorbitol was studied. Among the 273 sucrose-sensitive deletion mutants, 269 showed cross-sensitivities to sorbitol or NaCl, and four (i.e. ade5,7, ade6, ade8, and pde2) were specifically sensitive to high sucrose. The general stress response pathways via high-osmolarity glycerol and stress response element pathways and the function of the invertase in the ade mutants were similar to those in the wild-type strain. In the presence of high-sucrose stress, intracellular contents of ATP in ade mutants were at least twofold lower than that of the wild-type cells, suggesting that depletion of ATP is a factor in sensitivity to high-sucrose stress. The genes identified in this study might be important for tolerance to high-sucrose stress, and therefore should be target genes in future research into molecular modification for breeding of yeast tolerant to high-sucrose stress. [ABSTRACT FROM AUTHOR]

The article focuses on the glutamine synthetase (GS) of Pseudomonas taetrolens which can make theanine from glutamic acid and ethylamine in a assortment where yeast agitation of sugar is joined for adenosine triphosphate regeneration. The enzyme productivity in the aspect system was 30-fold greater than that in Pseudomonas taetrolens. Recombinant GS had the same properties as those of intrisic GS, and settled in the mixture of joined fermentation with energy shift.

Investigates the theanine production from glutamic acid and ethylamine as substrates using bacterial glutamine synthetase. Details on the physiological functions of theanine, an amino acid; Demand for theanine as a supplement for improving and/or maintaining human health; Characteristics of theanine production.

The freeze stress responses to prolonged storage at −20 °C in Torulaspora delbrueckii PYCC5323 were investigated. In this yeast, no loss of cell viability was observed for at least 120 days during freezing at −20 °C, whereas a loss of 80% was observed in a commercial baker’s yeast after 15 days. In the former strain, freeze resistance was dependent on an adaptation process. The primary cell target of freeze stress was the plasma membrane, preservation of its integrity being related with a lower increase of lipid peroxidation and with a higher resistance to H2O2, but not with the intracellular trehalose concentration. [Copyright &y& Elsevier]

Examines the isolation of yeast strains from dried sweet potatoes. Comparison of dough fermentation ability, freeze tolerance, and growth rates in molasses; Discovery that most stains isolated belonged to Saccharomyces cerevisiae; Measurement of the fermentation ability of high-sugar dough containing ONY1 strain; Growth rate of ONY1.