Strains Of Yeast Saccharomyces Cerevisiae Research Articles

GENOME SHUFFLING AS AN ALTERNATIVE METHOD OF IMPROVING THE PROPERTIES OF DISTILLERY YEAST

Abstract Modern technologies of bioethanol production require distillery yeast characterized by thermotolerance, osmotolerance and increased resistance to secondary metabolites. To date, no strains have been observed in nature which possess all of the above-mentioned characteristics. For many years, intensive research has been carried out to improve the technological properties of industrial strains. A number of methods have been developed to allow genetic improvement of distillery yeasts. One of the most promising and effective methods is genome shuffling, allowing the creation of hybrids whose genome is a combination of large DNA fragments derived from strains with distinct phenotypic traits. Genome shuffling creates a chance that the new strain will have valuable functional genes, including their full operons. This, in turn, increases the chance of a long-term maintenance of beneficial technological features by the obtained hybrids. 1. Introduction. 2. Yeast Saccharomyces cerevisiae. 2.1. Yeast genome. 2.2. Role of Saccharomyces cerevisiae yeast in the bioethanol production. 3. Pathways of genetic improvement. 4. Methods of genetic improvement. 5. Genome shuffling. 5.1. Improvement of Saccharomyces cerevisiae yeast strains by genome shuffling method. 6. Conclusion

Continuous production of bioethanol from sugarcane bagasse and downstream purification using membrane integrated bioreactor

Bioethanol is the most widely used transportation fuel and is often employed as an alternate to conventional petroleum fuel. The most important challenge in bioethanol production process is to achieve nearly pure ethanol by downstream purification. Production of ethanol from sugarcane bagasse was studied in a membrane integrated hybrid bioreactor for 115h using yeast strain Saccharomyces cerevisiae. The fermented product was subjected to continuous microfiltration after 20h of batch fermentation and 100% rejection of microorganism was achieved at this state. A maximum cell density of 2.4 of was reached in the fermenter during fermentation. The maximum cell density reached in the fermenter during fermentation was 2.4g/l. While studying the membrane performance during microfiltration, a flux decrease from 44.4l/m2h to 8.4l/m2h was observed after 65h of continuous filtration at constant 3bar transmembrane pressure. The permeate samples obtained from microfiltration were subjected to nanofiltration in order to recycle unconverted glucose from water ethanol mixture. During nanofiltration, the membrane performance revealed 58–86% rejection of glucose, a maximum ethanol concentration of 43.2g/l in the permeate and the reduction of membrane flux from 41.4l/m2h to 8.2l/m2h after 19h of continuous filtration at 10bar transmembrane pressure. This membrane based approach for bioethanol production employs a sustainable and clean technology which comes up with low or no waste generation.

Estrogenic Activities of Food Supplements and Beers as Assessed by a Yeast Bioreporter Assay

ABSTRACTMounting evidence of the effects of endocrine-disrupting chemicals (EDCs) in humans has led to assaying a vast array of food items (processed or packaged) as possible sources of human exposure to estrogens. In this study, we investigated the current situation in this respect of different food supplements and beer brands. Eleven food supplements and 24 beer brands were obtained from Helsinki, Finland. Sample preparation was carried out by established methods while estrogenic activities were assessed by a yeast bioluminescent assay, using two recombinant yeast strains (Saccharomyces cerevisiae BMAEREluc/ERα and S. cerevisiae BMA64/luc). All the food supplements as well as 81% of the beer samples tested were found to be estrogenic, with estradiol equivalent concentrations of food supplements and beer brands ranging from 7.5 to 11.5 µg/ml and from below detection limits to 43.6 ng/ml, respectively. The estrogenic activities detected in beer samples were not dependent on the beer's alcoholic content, the country of production, or the size of the production brewery. The results of our study imply that both food supplements and beers can be a significant source of human exposure to estrogens. Therefore, further studies and regular surveillance are warranted.

A new eremophilane sesquiterpene from the fungus Xylaria sp. V-27 and inhibition activity against degranulation in RBL-2H3 cells.

A new eremophilane sesquiterpene, 13,13-dimethoxyintegric acid (1), together with known compound integric acid (2) have been isolated from a fungus, Xylaria sp. V-27, obtained from a dead branch. The structure of 1 was established by means of spectroscopic analyses. 1 and 2 promoted growth restoring activity against the mutant yeast strain (Saccharomyces cerevisiae (zds1Δ erg3Δ pdr1Δ pdr3Δ)) and inhibited degranulation of rat basophilic leukemia RBL-2H3 cells stimulated by immnunoglobulin G + 2,4-dinitrophenylated-bovine serum albumin (IgE+DNP-BSA), thapsigargin and A23187.

Effects of the dose and viability of Saccharomyces cerevisiae. 2. Ruminal fermentation, performance of lactating dairy cows, and correlations between ruminal bacteria abundance and performance measures

This study examined effects of the dose and viability of supplemented Saccharomyces cerevisiae yeast strain YE1496 on ruminal fermentation and performance of lactating dairy cows. A second objective was to examine correlations between ruminal bacteria abundance and performance measures. Four ruminally cannulated lactating cows (284 ± 18 days in milk) were assigned randomly to 1 of 4 treatment sequences in a 4 × 4 Latin square experimental design using four 21-d experimental periods. Cows were fed a nonacidotic total mixed ration comprising 22.5% starch (minimum ruminal pH >5.8), 41.7% corn silage, 7.60% wet brewers grain, and 50.7% concentrate on a dry matter (DM) basis. The diet was supplemented with no yeast (control), a low (5.7 × 107 cfu/d; LLY) or high (6.0 × 108 cfu/d; HLY) dose of live yeast, or a high dose of killed yeast (6.0 × 108 cfu/d; killed by heating at 80°C for 1.5 h; HDY). Milk production and composition were measured twice daily from d 11 to 21 of each period, and rumen fluid samples were collected on d 21. In vivo digestibility was measured using chromic oxide as a marker. Pearson correlation analysis was used to assess whether animal performance parameters were correlated with relative abundance (RA) of ruminal bacteria. Supplemental LLY increased yields (kg/d) of milk (29.6 vs. 31.7) and milk protein (0.95 vs. 1.03), tended to increase milk fat yield (1.10 vs. 1.17) and ruminal acetate:propionate ratio (1.92 vs. 2.21), and increased in vivo apparent digestibility (%) of DM (64.5 vs. 69.1), neutral detergent fiber (NDF; 45.0 vs. 54.5), and ADF (53.1 vs. 60.9) compared with the control. Feeding HLY had no effects on milk yield compared with the control (30.0 vs. 29.6 kg/d). Feeding HDY tended to increase in vivo digestibility (%) of NDF (45.0 vs. 50.7), ADF (53.1 vs. 57.7), and the ruminal concentration of lactate (0.78 vs. 2.82 mM) but did not affect milk yield compared with the control. Dry matter and NDF digestibility correlated negatively with RA of unclassified Lachnospiraceae in both solid (r = -0.50 and -0.52, respectively) and liquid (r = -0.56 and -0.57, respectively) fractions, whereas milk yield correlated positively with RA of Lachnospiraceae [Ruminococcus] (an incompletely classified genus; r = 0.43) in the solid ruminal fraction. Supplemental LLY, HLY, or HDY increased or tended to increase DM, NDF, and ADF digestibility, but only LLY increased yields of milk, milk fat, and milk protein.

Fermentation Characteristics and Aromatic Profile of Plum Wines Produced with Indigenous Microbiota and Pure Cultures of Selected Yeast.

The aim of this study was to assess and compare fermentation characteristics and aromatic profile of plum wines produced with indigenous microbiota and pure cultures of different selected yeast. Experiments were carried out with plum (Prunus domestica L.) varieties of different fruit ripening times (Čačanska rana, Čačanska lepotica, and Požegača). Wine fermentations were conducted by the activity of indigenous microbiota, commercially available Saccharomyces cerevisiae and Saccharomyces bayanus yeast strains and joint activity of Schizosaccharomyces pombe and S. cerevisiae (sequential inoculation). Statistically significant differences in fermentative characteristics and the content of certain volatile compounds were observed as a result of metabolic activity of various indigenous and/or selected yeasts during fermentation of plum pomace. Minimal duration of fermentation (4 to 5 d) and fastest ethanol production rate (from 12.3 to 15.5 g/L/d) were the characteristics of the studied S. cerevisiae strains. Isobutanol, 3-methyl-1-butanol, 1-heptanol, and 1-octanol were the most prevalent higher alcohols in the tested plum wine samples. The predominant ester in plum wines was ethyl acetate, ethyl lactate, amyl acetate, isoamyl acetate, and ethyl palmitate, esters responsible for the floral and fruity olfactory tones, were also present in large amounts. Also, the use of S. cerevisiae strains resulted in the production of plum wines with better sensory characteristics than ones produced with other investigated yeasts. Obtained results are significant since there is limited data on the compounds responsible for the unique flavor of plum wine, as well as on the impact of different yeast starter cultures application on the overall quality of fruit wines.

Effect of Grape Temperature and Yeast Strain on Sauvignon blanc Wine Aroma Composition and Quality

The study focused on the production of Sauvignon blanc wines from grapes grown in sub-optimal climatic conditions. Grape temperatures of l0°C and 25°C at harvest, and fermentation with different Saccharomyces cerevisiae yeast strains, i.e. VIN 13, VIN 7, NT 116 and NT 7, were investigated over three seasons (1998, 1999 and 2000). The highest quality wines were produced from the cooler 10°C grapes. Choice of yeast strain was complicated by effects of factors such as grape temperature, grape maturity and season. In general, the highest ester concentrations and lowest higher alcohol concentrations were produced by NT 116, and the highest wine quality by NT 7. Strain VIN 7 yielded the lowest ester levels, which in some cases were preferred, since the masking effect of esters was diminished with the result that Sauvignon blanc wines with more pronounced cultivar-typical green notes and consequently higher quality could be produced. Therefore when Sauvignon blanc grapes, known to produce neutral wines, are used, factors such as low temperature at harvest and yeast strains suitable for these conditions should be considered.

Effect of Ascorbic Acid and Yeast Strain on Sauvignon blanc Wine Quality

Sauvignon blanc cultivar-typical aroma is affected by different components of which 2-methoxy-3-isobutylpyrazine and 4-mercapto-4-methylpentan-2-one are probably the most important. Climatic, viticultural and oenological conditions may have a prominent effect on the levels at which these impact aroma components occur in wine. Sauvignon blanc wines were produced from grapes from two climatically different regions. Different ascorbic acid/S02 combinations and different Saccharomyces cerevisiae yeast strains were used during the production of the wines. The wines were sensorially evaluated for specific wine characteristics, namely fruity/ester aroma intensity, grassy/green pepper aroma intensity, sulphur-like aroma intensity and overall wine quality. Significant differences were observed between treatments. A commercially available preparate (ascorbic acid/meta-bisulphite) and yeast strain VL3C produced sulphur-like, low-quality wines under the conditions of this investigation. The highest quality wines were produced from pure ascorbic acid/S02 treatments and fermentation by the yeast strain VIN 13.

Mimicking lichens: incorporation of yeast strains together with sucrose-secreting cyanobacteria improves survival, growth, ROS removal, and lipid production in a stable mutualistic co-culture production platform

BackgroundThe feasibility of heterotrophic–phototrophic symbioses was tested via pairing of yeast strains Cryptococcus curvatus, Rhodotorula glutinis, or Saccharomyces cerevisiae with a sucrose-secreting cyanobacterium Synechococcus elongatus.ResultsThe phototroph S. elongatus showed no growth in standard BG-11 medium with yeast extract, but grew well in BG-11 medium alone or supplemented with yeast nitrogen base without amino acids (YNB w/o aa). Among three yeast species, C. curvatus and R. glutinis adapted well to the BG-11 medium supplemented with YNB w/o aa, sucrose, and various concentrations of NaCl needed to maintain sucrose secretion from S. elongatus, while growth of S. cerevisiae was highly dependent on sucrose levels. R. glutinis and C. curvatus grew efficiently and utilized sucrose produced by the partner in co-culture. Co-cultures of S. elongatus and R. glutinis were sustained over 1 month in both batch and in semi-continuous culture, with the final biomass and overall lipid yields in the batch co-culture 40 to 60% higher compared to batch mono-cultures of S. elongatus. The co-cultures showed enhanced levels of palmitoleic and linoleic acids. Furthermore, cyanobacterial growth in co-culture with R. glutinis was significantly superior to axenic growth, as S. elongatus was unable to grow in the absence of the yeast partner when cultivated at lower densities in liquid medium. Accumulated reactive oxygen species was observed to severely inhibit axenic growth of cyanobacteria, which was efficiently alleviated through catalase supply and even more effectively with co-cultures of R. glutinis.ConclusionsThe pairing of a cyanobacterium and eukaryotic heterotroph in the artificial lichen of this study demonstrates the importance of mutual interactions between phototrophs and heterotrophs, e.g., phototrophs provide a carbon source to heterotrophs, and heterotrophs assist phototrophic growth and survival by removing/eliminating oxidative stress. Our results establish a potential stable production platform that combines the metabolic capability of photoautotrophs to capture inorganic carbon with the channeling of the resulting organic carbon directly to a robust heterotroph partner for producing biofuel and other chemical precursors.

Both R-loop removal and ribonucleotide excision repair activities of RNase H2 contribute substantially to chromosome stability

Cells carrying deletions of genes encoding H-class ribonucleases display elevated rates of chromosome instability. The role of these enzymes is to remove RNA-DNA associations including persistent mRNA-DNA hybrids (R-loops) formed during transcription, and ribonucleotides incorporated into DNA during replication. RNases H1 and H2 can degrade the RNA component of R-loops, but only RNase H2 can initiate accurate ribonucleotide excision repair (RER). In order to examine the specific contributions of these activities to chromosome stability, we measured rates of loss-of-heterozygosity (LOH) in diploid Saccharomyces cerevisiae yeast strains carrying the rnh201-RED separation-of-function allele, encoding a version of RNase H2 that is RER-defective, but partly retains its other activity. The LOH rate in rnh201-RED was intermediate between RNH201 and rnh201Δ. In strains carrying a mutant version of DNA polymerase ε (pol2-M644G) that incorporates more ribonucleotides than normal, the LOH rate in rnh201-RED was as high as the rate measured in rnh201Δ. Topoisomerase 1 cleavage at sites of ribonucleotide incorporation has been recently shown to produce DNA double strand breaks. Accordingly, in both the POL2 and pol2-M644G backgrounds, the LOH elevation in rnh201-RED was suppressed by top1Δ. In contrast, in strains that incorporate fewer ribonucleotides (pol2-M644L) the LOH rate in rnh201-RED was low and independent of topoisomerase 1. These results suggest that both R-loop removal and RER contribute substantially to chromosome stability, and that their relative contributions may be variable across different regions of the genome. In this scenario, a prominent contribution of R-loop removal may be expected at highly transcribed regions, whereas RER may play a greater role at hotspots of ribonucleotide incorporation.

Influence of structure of lactones with the methylcyclohexene and dimethylcyclohexene ring on their biotransformation and antimicrobial activity.

The aim of this article is influence of the structure of lactones with the methylcyclohexene and dimethylcyclohexene ring on their biotransformation and antimicrobial activity. This work was based on the general remark that even the smallest change in the structure of a compound can affect its biological properties. The results of the biotransformation of four bicyclic unsaturated lactones with one or two methyl groups in the cyclohexene ring was tested using fifteen fungal strains (Fusarium species, Penicillium species, Absidia species, Cunninghamella japonica, and Pleurotus ostreatus) and five yeast strains (Yarrowia lipolytica, Rhodorula marina, Rhodorula rubra, Candida viswanathii, and Saccharomyces cerevisiae). During these transformations, new epoxylactone and hydroxylactone were obtained. The relationship between the substrate structure and the ability of the microorganisms to transform them were analysed. Only compounds with C-O bond of lactone ring in the equatorial position were transformed by fungus. All presented here lactones were examined also for their antimicrobial activity. It turned out that these compounds exhibited growth inhibition of bacteria and fungi, mainly Bacillus subtilis, Candida albicans, Aspergillus niger, and Penicillium expansum.

Understanding the responses of Saccharomyces cerevisiae yeast strain during dehydration processes using synchrotron infrared spectroscopy.

For the first time, synchrotron infrared spectroscopy was performed on yeast during dehydration processes in real time with simultaneously controlled relative humidity and temperature. This led us to investigate the biochemical modification in relation to the dehydration of Saccharomyces cerevisiae. The correlation between the hydration level and yeast survival was observed. Following the test conditions, the modification of the protein structure was observed. However, no evident modification of the lipid composition resulting from dehydration was observed. Furthermore, the results showed that the medium rich in nutrients and glutathione precursors can improve yeast survival during dehydration at 45 °C. This could be related to the high relative amounts of CH3 groups in the lipid composition assigned to the low lipid oxidation level in this case. Our work demonstrated the feasibility of using S-FTIR for investigating yeast responses to dehydration processes in real time. This method can be used for understanding the effect of dehydration/rehydration on the biochemical modification of yeast.

Chemical and Volatile Composition of Mango Wines Fermented with Different Saccharomyces cerevisiae Yeast Strains

The aim of this study was to compare the chemical and volatile composition of mango wines fermented with Saccharomyces cerevisiae var. bayanus EC1118, S. cerevisiae var. chevalieri CICC1028 and S. cerevisiae var. cerevisiae MERIT.ferm. Strains EC1118 and MERIT.ferm showed similar growth patterns but strain CICC1028 grew slightly slowly. The ethanol level reached about 8% (v/v) for each mango wine and sugars (glucose, fructose and sucrose) were almost exhausted at the end of fermentation. There were only negligible changes in the concentrations of citric, succinic and tartaric acids, except for malic acid (decreased significantly). Different volatile compounds were produced, which were mainly fatty acids, alcohols and esters. Most volatiles that were present in the juice were consumed to trace amounts. The kinetic changes of volatiles were similar among the three yeasts but the concentrations of some volatiles varied with yeast. Strain MERIT.ferm produced higher amounts of higher alcohols, isoamyl and 2-phenylethyl acetates, whereas strain CICC1028 produced higher amounts of medium-chain fatty acids and ethyl esters of decanoate and dodecanoate. These results suggest that it may be possible to produce mango wines with differential characteristics using different S. cerevisiae strains.

Candida zemplinina for Production of Wines with Less Alcohol and More Glycerol

We developed a new protocol for winery mixed fermentations, using the selected Candida zemplinina yeast strain Cz3. The results of a two-year study, in which red musts (Merlot in 2010; Merlot, Nero d’Avola and Frappato in 2011) were inoculated with Cz3, is discussed. These wines were compared with wines obtained by inoculation with commercial Saccharomyces cerevisiae yeast strains (NDA21 and AR06 in 2010; NDA21 in 2011), or with those obtained by spontaneous fermentation (only in 2011). The inoculation of Cz3 always resulted in a two-phase fermentation: the first phase was driven by the C. zemplinina strain, while the second was dominated by the indigenous S. cerevisiae yeasts coming from the grapes and/or the winery. In both years the Cz3 wines contained less alcohol and more glycerol than those made with the commercial yeast strains or those obtained by spontaneous fermentation. Triangle tests showed that a sensorial difference between wines could only be achieved through the utilisation of Cz3.

Production of phenylacetic acid from l-phenylalanine in dual reactor membrane hybrid system

Some natural substances are impossible to produce directly using one strain of microorganisms; they have to be produced via one or more intermediates requiring the use of different production strains. After each separate production process, downstream processing of the product is necessary to prepare the substrate for another production step. In this work, two step bioproduction of phenylacetic acid from l-phenylalanine through precursor 2-phenylethanol was performed using a dual reactor membrane hybrid system. This hybrid system consisted of two bioreactors mutually interconnected with immersed capillary membrane modules used for precursor transport between the bioreactors. In the first bioreactor, 2-phenylethanol was produced by the yeast strain Saccharomyces cerevisiae; in the second bioreactor, 2-phenylethanol was transformed by the bacterial strain Gluconobacter oxydans. Extraction capability of the hybrid system was tested by a series of membrane extraction experiments. In such a system, biotransformation experiments with 2-phenylethanol bioproduction from l-phenylalanine and its biotransformation to phenylacetic acid in non-growth conditions were carried out using free cells of Gluconobacter oxydans and the cells immobilized in lenticular LentiKats® particles.

Optimization of fermentation conditions for Chinese bayberry wine by response surface methodology and its qualities

Colour and flavour are both important challenges for bayberry wine production because of a shortage of selected strains. The yeast Saccharomyces cerevisiae strain YF152, separated from a natural Chinese bayberry fermentation mash [alcohol tolerance capacity (18.0%), SO2 (200 mg/L), sugar content (40%) and pH (2.50)] was employed to brew Chinese bayberry wine. Response surface methodology was used to simultaneously analyse the effects of the fermentation conditions on Chinese bayberry wine. The optimum conditions were found to be a temperature of 26.5 °C, an initial sugar content of 22.0°Brix, an inoculum size of 4.0% and an initial pH of 2.90. Under these conditions, the final alcohol content of the bayberry wine was 13.4%, the anthocyanin content was 77 mg/L and the residual sugar content was 1 g/L. These numbers agreed well with the predicted values. The major characteristic flavour components of the wine were 3-methyl-1-butanol, 2-phenylethanol, ethyl acetate, 2-methylbutyl acetate and acetic acid. Copyright © 2016 The Institute of Brewing & Distilling

Cell wall polysaccharides released during the alcoholic fermentation by Schizosaccharomyces pombe and S. japonicus: quantification and characterization

The present work demonstrates that yeasts belonging to the Schizosaccharomyces genus release a high quantity of polysaccharides of cell wall origin starting from the onset of the alcoholic fermentation. By the end of the alcoholic fermentation, all of the Schizosaccharomyces yeast strains released a quantity of polysaccharides approximately 3–7 times higher than that released by a commercial Saccharomyces cerevisiae yeast strain under the same fermentative conditions of synthetic juice. A higher content of polysaccharide was found in media fermented by Schizosaccharomyces japonicus with respect to that of Schizosaccharomyces pombe. Some of the strains evaluated were also able to produce high levels of pyruvic acid, which has been shown to be an important compound for color stability of wine. The presence of strains with different malic acid consumption patterns along with high polysaccharide release would enable production of naturally modified wines with enhanced mouth feel and reduced acidity. The chemical analysis of the released polysaccharides demonstrated divergence between the two yeast species S. pombe and S. japonicus. A different mannose/galactose ratio and a different percentage of proteins was observed on the polysaccharides released by S. pombe as compared to S. japonicus. Analysis of the proteins released in the media revealed the presence of a glycoprotein with a molecular size around 32–33 kDa only for the species S. japonicus. Mass spectrometry analysis of carbohydrate moieties showed similar proportions among the N-glycan chains released in the media by both yeast species but differences between the two species were also observed. These observations suggest a possible role of rapid MALDI-TOF screening of N-glycans compositional fingerprint as a taxonomic tool for this genus. Polysaccharides release in the media, in particular galactomannoproteins in significant amounts, could make these yeasts particularly interesting also for the industrial production of exogenous polysaccharide preparations.

Impact of Commercial Strain Use on Saccharomyces cerevisiae Population Structure and Dynamics in Pinot Noir Vineyards and Spontaneous Fermentations of a Canadian Winery.

Wine is produced by one of two methods: inoculated fermentation, where a commercially-produced, single Saccharomyces cerevisiae (S. cerevisiae) yeast strain is used; or the traditional spontaneous fermentation, where yeast present on grape and winery surfaces carry out the fermentative process. Spontaneous fermentations are characterized by a diverse succession of yeast, ending with one or multiple strains of S. cerevisiae dominating the fermentation. In wineries using both fermentation methods, commercial strains may dominate spontaneous fermentations. We elucidate the impact of the winery environment and commercial strain use on S. cerevisiae population structure in spontaneous fermentations over two vintages by comparing S. cerevisiae populations in aseptically fermented grapes from a Canadian Pinot Noir vineyard to S. cerevisiae populations in winery-conducted fermentations of grapes from the same vineyard. We also characterize the vineyard-associated S. cerevisiae populations in two other geographically separate Pinot Noir vineyards farmed by the same winery. Winery fermentations were not dominated by commercial strains, but by a diverse number of strains with genotypes similar to commercial strains, suggesting that a population of S. cerevisiae derived from commercial strains is resident in the winery. Commercial and commercial-related yeast were also identified in the three vineyards examined, although at a lower frequency. There is low genetic differentiation and S. cerevisiae population structure between vineyards and between the vineyard and winery that persisted over both vintages, indicating commercial yeast are a driver of S. cerevisiae population structure. We also have evidence of distinct and persistent populations of winery and vineyard-associated S. cerevisiae populations unrelated to commercial strains. This study is the first to characterize S. cerevisiae populations in Canadian vineyards.

Leveraging Genetic-Background Effects in Saccharomyces cerevisiae To Improve Lignocellulosic Hydrolysate Tolerance.

A major obstacle to sustainable lignocellulosic biofuel production is microbe inhibition by the combinatorial stresses in pretreated plant hydrolysate. Chemical biomass pretreatment releases a suite of toxins that interact with other stressors, including high osmolarity and temperature, which together can have poorly understood synergistic effects on cells. Improving tolerance in industrial strains has been hindered, in part because the mechanisms of tolerance reported in the literature often fail to recapitulate in other strain backgrounds. Here, we explored and then exploited variations in stress tolerance, toxin-induced transcriptomic responses, and fitness effects of gene overexpression in different Saccharomyces cerevisiae (yeast) strains to identify genes and processes linked to tolerance of hydrolysate stressors. Using six different S. cerevisiae strains that together maximized phenotypic and genetic diversity, first we explored transcriptomic differences between resistant and sensitive strains to identify common and strain-specific responses. This comparative analysis implicated primary cellular targets of hydrolysate toxins, secondary effects of defective defense strategies, and mechanisms of tolerance. Dissecting the responses to individual hydrolysate components across strains pointed to synergistic interactions between osmolarity, pH, hydrolysate toxins, and nutrient composition. By characterizing the effects of high-copy gene overexpression in three different strains, we revealed the breadth of the background-specific effects of gene fitness contributions in synthetic hydrolysate. Our approach identified new genes for engineering improved stress tolerance in diverse strains while illuminating the effects of genetic background on molecular mechanisms. Recent studies on natural variation within Saccharomyces cerevisiae have uncovered substantial phenotypic diversity. Here, we took advantage of this diversity, using it as a tool to infer the effects of combinatorial stress found in lignocellulosic hydrolysate. By comparing sensitive and tolerant strains, we implicated primary cellular targets of hydrolysate toxins and elucidated the physiological states of cells when exposed to this stress. We also explored the strain-specific effects of gene overexpression to further identify strain-specific responses to hydrolysate stresses and to identify genes that improve hydrolysate tolerance independent of strain background. This study underscores the importance of studying multiple strains to understand the effects of hydrolysate stress and provides a method to find genes that improve tolerance across strain backgrounds.

Antioxidant activity of thermal or non-thermally treated strawberry and mango juices by Saccharomyces cerevisiae growth based assays

The antioxidant activity of strawberry or mango juice [untreated or treated by high intensity pulsed electric fields (HIPEF) or heat] has been studied on a Saccharomyces cerevisiae yeast strain exposed to different oxidants (tert-butyl hydroperoxide, diamide and diethyl maleate). Cellular biomass production was higher in the juices compared to the synthetic medium, which contained all required amino acids, nitrogen bases and vitamins needed for growth, indicating that growth-limiting nutrient concentrations in the natural juices were higher. In addition, the inhibitory effect of tert-butyl hydroperoxide or diamide in yeast growth was lower in the juices compared to synthetic medium, supporting an antioxidant effect of both juices. In contrast, juices did not confer significant protection against diethyl maleate. HIPEF or thermal treatments did not negatively influence the antioxidant activity of the juices. In fact, HIPEF-treated strawberry juices presented enhanced antioxidant effect on yeast cell growth in the presence of tert-butyl hydroperoxide compared to fresh juice in terms of adaptation period and the final cellular biomass.