Showing papers on "Yeast published in 2019"
TL;DR: This review is dedicated to discuss on significant characteristics of the most common methylotrophic and non-methylotrophic yeast expression systems with an emphasis on their advantages and new developments.
Abstract: Yeasts are outstanding hosts for the production of functional recombinant proteins with industrial or medical applications. Great attention has been emerged on yeast due to the inherent advantages and new developments in this host cell. For the production of each specific product, the most appropriate expression system should be identified and optimized both on the genetic and fermentation levels, considering the features of the host, vector and expression strategies. Currently, several new systems are commercially available; some of them are private and need licensing. The potential for secretory expression of heterologous proteins in yeast proposed this system as a candidate for the production of complex eukaryotic proteins. The common yeast expression hosts used for recombinant proteins' expression include Saccharomyces cerevisiae, Pichia pastoris, Hansenula polymorpha, Yarrowia lipolytica, Arxula adeninivorans, Kluyveromyces lactis, and Schizosaccharomyces pombe. This review is dedicated to discuss on significant characteristics of the most common methylotrophic and non-methylotrophic yeast expression systems with an emphasis on their advantages and new developments.
101 citations
TL;DR: This study constructed a PPD-producing chassis via modular engineering of the mevalonic acid pathway and optimization of P450 expression levels and established a series of cell factories to produce ginsenoside Rh2, which was optimized by improving the C3–OH glycosylation efficiency.
Abstract: Synthetic biology approach has been frequently applied to produce plant rare bioactive compounds in microbial cell factories by fermentation. However, to reach an ideal manufactural efficiency, it is necessary to optimize the microbial cell factories systemically by boosting sufficient carbon flux to the precursor synthesis and tuning the expression level and efficiency of key bioparts related to the synthetic pathway. We previously developed a yeast cell factory to produce ginsenoside Rh2 from glucose. However, the ginsenoside Rh2 yield was too low for commercialization due to the low supply of the ginsenoside aglycone protopanaxadiol (PPD) and poor performance of the key UDP-glycosyltransferase (UGT) (biopart UGTPg45) in the final step of the biosynthetic pathway. In the present study, we constructed a PPD-producing chassis via modular engineering of the mevalonic acid pathway and optimization of P450 expression levels. The new yeast chassis could produce 529.0 mg/L of PPD in shake flasks and 11.02 g/L in 10 L fed-batch fermentation. Based on this high PPD-producing chassis, we established a series of cell factories to produce ginsenoside Rh2, which we optimized by improving the C3–OH glycosylation efficiency. We increased the copy number of UGTPg45, and engineered its promoter to increase expression levels. In addition, we screened for more efficient and compatible UGT bioparts from other plant species and mutants originating from the direct evolution of UGTPg45. Combining all engineered strategies, we built a yeast cell factory with the greatest ginsenoside Rh2 production reported to date, 179.3 mg/L in shake flasks and 2.25 g/L in 10 L fed-batch fermentation. The results set up a successful example for improving yeast cell factories to produce plant rare natural products, especially the glycosylated ones.
95 citations
TL;DR: It is demonstrated that acetate uptake pathway in oleaginous yeast (Yarrowia lipolytica) could function as an acetyl-CoA shortcut to achieve metabolic optimality in producing polyketides and highlights that low-cost acetic acid could be sustainably upgraded to high-value polyketide species in an eco-friendly and cost-efficient manner.
94 citations
TL;DR: This review argues the importance and benefits of xylose utilization as not only a way of expanding a substrate range, but also an effective environmental perturbation for the efficient production of advanced biofuels and chemicals in yeasts.
87 citations
TL;DR: The level of yeast biocontrol efficacy through the production of volatiles could be the result of a synergistic effect between VOCs and carbon dioxide in the packaging environment.
77 citations
TL;DR: In this article, the importance of yeast in the production of functional food and development of bioprocesses for the production high value nutraceuticals is discussed. But, there is a need for exploration of novel yeast strains that have the ability to produce novel and efficient biocatalysts from traditional fermented foods for advances in food industry bio-processes.
Abstract: Background Biotechnological potential of yeasts can be evidenced by the rich history of its application in food fermentation. Several yeast species isolated from fermented foods have been characterised and applied as starter/co-starter in functional food industries. The outcome of modern research in the recent past on nutraceuticals and development of functional foods using yeasts suggests its bright future in food biotechnology. Scope and approach In this article, bioactive compounds produced using yeasts including β-glucan, carotenoids, glutathione, bioactive peptides, γ-aminobutyric acid, organic selenium, prebiotic oligosaccharides and free polyphenols, are discussed. Yeast species having probiotic potential as well as therapeutic properties are highlighted in the manuscript. Recent studies on metabolic engineering approaches applied to develop yeast strains with additional functional properties with higher industrial importance have also been reviewed. Key Findings and Conclusions: The current review summarizes the importance of yeast in the production of functional food and development of bioprocesses for the production of high value nutraceuticals. The review also highlights the importance of yeast as a single starter as well as a component of mixed starter cultures in production of bioactive metabolites. However, there is a need of exploration of novel yeast strains that have the ability to produce novel and efficient biocatalysts from traditional fermented foods for advances in food industry bioprocesses.
76 citations
TL;DR: The recent advances in the use of the four most popular oleaginous yeasts for making lipids and other potential fuels are described - Yarrowia lipolytica, Lipomyces starkeyi, Rhodosporidium toruloides, and Cutaneotrichosporon oleaginosus.
70 citations
TL;DR: The results, as well the availability of endogenous NAD-dependent formate dehydrogenase, indicate that yeast might be an especially suitable host for engineering growth on formate, and find the reductive glycine pathway to be highly active in this host.
Abstract: One-carbon (C1) compounds are attractive microbial feedstocks as they can be efficiently produced from widely available resources. Formate, in particular, represents a promising growth substrate, as it can be generated from electrochemical reduction of CO2 and fed to microorganisms in a soluble form. We previously identified the synthetic reductive glycine pathway as the most efficient route for aerobic growth on formate. We further demonstrated pathway activity in Escherichia coli after expression of both native and foreign genes. Here, we explore whether the reductive glycine pathway could be established in a model microorganism using only native enzymes. We used the yeast Saccharomyces cerevisiae as host and show that overexpression of only endogenous enzymes enables glycine biosynthesis from formate and CO2 in a strain that is otherwise auxotrophic for glycine. We find the pathway to be highly active in this host, where 0.125 mM formate is sufficient to support growth. Notably, the formate-dependent g...
69 citations
TL;DR: It is demonstrated that improving phosphoenolpyruvate supply by expressing pyruvates kinase variants and eliminating the formation of p-hydroxy-phenylethanol without creating tyrosine auxotrophy significantly contributed to improve 2PE production in S. cerevisiae.
69 citations
TL;DR: The design and construction of artificial PUFA biosynthetic gene clusters (BGCs) encoding polyketide synthase-like PUFA synthases from myxobacteria adapted for the oleaginous yeast Y. lipolytica capable of producing a high concentration of PUFAs are demonstrated.
Abstract: Long-chain polyunsaturated fatty acids (LC-PUFAs), particularly the omega-3 LC-PUFAs eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA), have been associated with beneficial health effects. Consequently, sustainable sources have to be developed to meet the increasing demand for these PUFAs. Here, we demonstrate the design and construction of artificial PUFA biosynthetic gene clusters (BGCs) encoding polyketide synthase-like PUFA synthases from myxobacteria adapted for the oleaginous yeast Yarrowia lipolytica. Genomic integration and heterologous expression of unmodified or hybrid PUFA BGCs yielded different yeast strains with specific LC-PUFA production profiles at promising yield and thus valuable for the biotechnological production of distinct PUFAs. Nutrient screening revealed a strong enhancement of PUFA production, when cells were phosphate limited. This represents, to the best of our knowledge, highest concentration of DHA (16.8 %) in total fatty acids among all published PUFA-producing Y. lipolytica strains. Sustainable sources are needed to meet the demand for long-chain polyunsaturated fatty acids. Here the authors construct an artificial biosynthetic gene cluster in Y. lipolytica capable of producing a high concentration of PUFAs.
68 citations
TL;DR: In this article, the potential effects of yeast and carrot extracts, and their associated mechanisms in the alleviation of seawater-induced salt stress in maize, were investigated, and it was shown that pretreatment of maize seeds with yeast or carrot extract provided maize plants with enormous abilities in reducing growth inhibition and biomass loss when exposed to seawater.
Abstract: Damage to plant productivity due to soil salinity is a major agricultural problem, necessitating the development of effective salinity management measures. Here, we sought the potential effects of yeast and carrot extracts, and their associated mechanisms in the alleviation of seawater-induced salt stress in maize. Pretreatment of maize seeds with yeast or carrot extract provided maize plants with enormous abilities in reducing growth inhibition and biomass loss when exposed to seawater. The better growth performance of yeast extract- and carrot extract-primed plants under saline conditions coincided with improved protection of the photosynthetic pigments, chlorophylls and carotenoids. The primed plants also restricted Na+ accumulation in both roots and shoots while maintaining a higher K+ content and lower Na+/K+ ratio when compared with that of non-primed plants. Yeast extract and carrot extract also potentiated salt tolerance mechanisms by accelerating the production of osmolytes, as evidenced by accumulating levels of total free amino acids and soluble sugars, especially in the roots of primed plants during salinity. The enhanced levels of ascorbic acid and phenolic compounds, and the heightened activities of reactive oxygen species-detoxifying enzymes superoxide dismutase, catalase, and ascorbate peroxidase with concurrent reduction of lipid peroxidation in the leaves of primed plants clearly indicated a positive impact of yeast extract- and carrot extract-priming on the antioxidant system of maize under salt stress. Our results together suggest decisive roles of yeast extract and carrot extract in the management of salt-induced adverse effects in economically important maize, and perhaps other crops.
TL;DR: Functional analysis of the four metagenomic data sets was possible to link the production of lactic acid, acetic acid, ethanol, and carbon dioxide to subgroups of the microbial species found, including L. aquikefiri, whereas glycerol production was associated with S. cerevisiae.
Abstract: Water kefir is a fruity, sour, slightly alcoholic and carbonated beverage, which is made by fermentation of an aqueous sucrose solution in the presence of dried figs and water kefir grains. These polysaccharide grains contain lactic acid bacteria (LAB), yeasts, and sometimes bifidobacteria and/or acetic acid bacteria, which consume sucrose to produce exopolysaccharides, lactic acid, acetic acid, ethanol, and carbon dioxide. Shotgun metagenomic sequencing was used to examine the microbial species diversity present at two time points during water kefir fermentation in detail, both in the water kefir liquor and on the water kefir grains, hence representing four samples. Lactobacillus harbinensis, Lactobacillus hilgardii, Lactobacillus nagelii, Lactobacillus paracasei, and a Lactobacillus species similar to Lactobacillus hordei/mali were present in the water kefir examined, along with Bifidobacterium aquikefiri and two yeast species, namely Saccharomyces cerevisiae and Dekkera bruxellensis. In addition, evidence for a novel Oenococcus species related to Oenococcus oeni and Oenococcus kitaharae was found. Its genome was derived from the metagenome and made available under the name of Candidatus Oenococcus aquikefiri. Through functional analysis of the four metagenomic data sets, it was possible to link the production of lactic acid, acetic acid, ethanol, and carbon dioxide to subgroups of the microbial species found. In particular, the production of mannitol from fructose was linked to L. hilgardii, Candidatus O. aquikefiri, and B. aquikefiri, whereas glycerol production was associated with S. cerevisiae. Also, there were indications of cross-feeding, for instance in the case of amino acid supply. Few bacterial species could synthesize a limited number of cofactors, making them reliant on the figs or S. cerevisiae. The LAB species in turn were found to be capable of contributing to water kefir grain growth, as dextransucrase-encoding genes were attributed to L. hilgardii, L. hordei/mali, and Candidatus O. aquikefiri.
TL;DR: The consequences of nitrogen addition are presented, discussing the sources, time of addition, transcriptome changes, and effect on volatile compound composition.
TL;DR: This work discovered that head-modifying CoQ pathway components selectively colocalize to multiple resolvable domains in vivo, representing supramolecular assemblies and suggests that CoQ domains function to facilitate substrate accessibility for processive and efficient CoQ production and distribution in cells.
Abstract: Coenzyme Q (CoQ) lipids are ancient electron carriers that, in eukaryotes, function in the mitochondrial respiratory chain. In mitochondria, CoQ lipids are built by an inner membrane-associated, multicomponent, biosynthetic pathway via successive steps of isoprenyl tail polymerization, 4-hydroxybenzoate head-to-tail attachment, and head modification, resulting in the production of CoQ. In yeast, we discovered that head-modifying CoQ pathway components selectively colocalize to multiple resolvable domains in vivo, representing supramolecular assemblies. In cells engineered with conditional ON or OFF CoQ pathways, domains were strictly correlated with CoQ production and substrate flux, respectively, indicating that CoQ lipid intermediates are required for domain formation. Mitochondrial CoQ domains were also observed in human cells, underscoring their conserved functional importance. CoQ domains within cells were highly enriched adjacent to ER-mitochondria contact sites. Together, our data suggest that CoQ domains function to facilitate substrate accessibility for processive and efficient CoQ production and distribution in cells.
TL;DR: In conclusion, the yeast grown in media with potato wastewater supplemented with 3% or 5% glycerol synthesized carotenoids, and their content in biomass did not exceed 230 μg/gd, and the level of pollution reduction by media was determined to be low.
Abstract: The objective of this study was to determine the possibility of simultaneous biosynthesis of lipids and carotenoids by the Rhodotorula yeast strains in media with waste glycerol and deproteinized potato wastewater and to determine the level of pollution reduction by media. On the basis of results obtained during the yeast microcultures in the Bioscreen C system, it was found that potato wastewater and glycerol can be used as components of media for Rhodotorula glutinis, Rhodotorula mucilaginosa, and Rhodotorula gracilis yeast strains. The amount of glycerol added to media higher than 10% significantly decreased the growth rate of yeast. The results of yeast culture in the laboratory shaker flasks showed a possibility of simultaneous production of lipids and carotenoids by R. glutinis, R. mucilaginosa, and R. gracilis yeast strains during cultivation in media containing only waste glycerol and deproteinized potato wastewater. A higher intracellular lipid content (approximately 15 g/100 gd.w.) was obtained for R. mucilaginosa and R. gracilis yeast biomass after cultivation in experimental media with waste glycerol and potato wastewater. In conclusion, the yeast grown in media with potato wastewater supplemented with 3% or 5% glycerol synthesized carotenoids, and their content in biomass did not exceed 230 μg/gd.w.
TL;DR: In this paper, the authors explored the possibilities of using unconventional and cost-effective substrates as well as nitrogen supplements in high gravity and very high gravity (VHG) fermentations.
TL;DR: Phenolic acid metabolism in sourdoughs was enhanced by co-fermentation with strains exhibiting complementary metabolic activities, and results may enable improvement of bread quality by targeted conversion of phenolic acids during Sourdough fermentation.
TL;DR: Results identify Snf2 as a regulator of antifungal activity and pulcherriminic acid biosynthesis in M. pulcherima and provide a starting point for deciphering the molecular functions underlying the antagonistic activity of this yeast.
Abstract: Metschnikowia pulcherrima synthesises the pigment pulcherrimin, from cyclodileucine (cyclo(Leu-Leu)) as a precursor, and exhibits strong antifungal activity against notorious plant pathogenic fungi. This yeast therefore has great potential for biocontrol applications against fungal diseases; particularly in the phyllosphere where this species is frequently found. To elucidate the molecular basis of the antifungal activity of M. pulcherrima, we compared a wild-type strain with a spontaneously occurring, pigmentless, weakly antagonistic mutant derivative. Whole genome sequencing of the wild-type and mutant strains identified a point mutation that creates a premature stop codon in the transcriptional regulator gene SNF2 in the mutant. Complementation of the mutant strain with the wild-type SNF2 gene restored pigmentation and recovered the strong antifungal activity. Mass spectrometry (UPLC HR HESI-MS) proved the presence of the pulcherrimin precursors cyclo(Leu-Leu) and pulcherriminic acid and identified new precursor and degradation products of pulcherriminic acid and/or pulcherrimin. All of these compounds were identified in the wild-type and complemented strain, but were undetectable in the pigmentless snf2 mutant strain. These results thus identify Snf2 as a regulator of antifungal activity and pulcherriminic acid biosynthesis in M. pulcherrima and provide a starting point for deciphering the molecular functions underlying the antagonistic activity of this yeast.
TL;DR: Findings suggest that yeast polysaccharides have potentials as anti-inflammatory drugs or adjuvants in the intestinal inflammation therapy.
TL;DR: The results indicate that selenium may induce lipid peroxidation, which consequently affects the loss of integrity of the cytoplasmic membrane and can be used to prepare a novel formula of dietary supplements, which can be applied directly to various diets for both humans and animals.
Abstract: This article discusses the effect of selenium in aqueous solutions on aspects of lipid and amino acid metabolism in the cell biomass of Saccharomyces cerevisiae MYA-2200 and Candida utilis ATCC 9950 yeasts. The yeast biomass was obtained by using waste products (potato wastewater and glycerol). Selenium, at a dose of 20 mg/L of aqueous solution, affected the differentiation of cellular morphology. Yeast enriched with selenium was characterized by a large functional diversity in terms of protein and amino acid content. The protein content in the biomass of S. cerevisiae enriched with selenium (42.6%) decreased slightly as compared to that in the control sample without additional selenium supplementation (48.4%). Moreover, yeasts of both strains enriched with selenium contained a large amount of glutamic acid, aspartic acid, lysine, and leucine. Analysis of fatty acid profiles in S. cerevisiae yeast supplemented with selenium showed an increase in the unsaturated fatty acid content (e.g., C18:1). The presence of margaric acid (C17:0) and hexadecanoic acid (C17:1) was found in the C. utilis biomass enriched with selenium, in contrast to that of S. cerevisiae. These results indicate that selenium may induce lipid peroxidation, which consequently affects the loss of integrity of the cytoplasmic membrane. Yeast enriched with selenium with optimal amino acid and lipid composition can be used to prepare a novel formula of dietary supplements, which can be applied directly to various diets for both humans and animals.
TL;DR: It is demonstrated that the yeast species Saccharomyces cerevisiae and Yarrowia lipolytica both can be engineered to produce 2'-fucosyllactose (2'FL), which is the most abundant oligosaccharide in human breast milk, at high titer and productivity.
TL;DR: In this paper, the authors aimed at isolating and identifying yeast species from two types of traditional kefir grains and establishing some potential probiotic properties including survival in the gastrointestinal tract, auto-aggregation, hydrophobicity and hydrolytic enzymes production.
TL;DR: Three different technologies are combined to develop a more efficient conversion process for each of these feedstocks, including diluted alkaline deacetylation process, combined thermochemical and mechanical shear pretreatment, and fermentation using a combined inoculum of two commercial Saccharomyces yeast strains.
TL;DR: It is proved that the de novo purine biosynthesis genes are useful targets for metabolic engineering of yeast stress tolerance and can be employed for efficient lignocellulosic biorefinery to produce biofuels and biochemicals.
Abstract: Yeast strains that are tolerant to multiple environmental stresses are highly desired for various industrial applications. Despite great efforts in identifying key genes involved in stress tolerance of budding yeast Saccharomyces cerevisiae, the effects of de novo purine biosynthesis genes on yeast stress tolerance are still not well explored. Our previous studies showed that zinc sulfate addition improved yeast acetic acid tolerance, and key genes involved in yeast stress tolerance were further investigated in this study. Three genes involved in de novo purine biosynthesis, namely, ADE1, ADE13, and ADE17, showed significantly increased transcription levels by zinc sulfate supplementation under acetic acid stress, and overexpression of these genes in S. cerevisiae BY4741 enhanced cell growth under various stress conditions. Meanwhile, ethanol productivity was also improved by overexpression of the three ADE genes under stress conditions, among which the highest improvement attained 158.39% by ADE17 overexpression in the presence of inhibitor mixtures derived from lignocellulosic biomass. Elevated levels of adenine-nucleotide pool “AXP” ([ATP] + [ADP] + [AMP]) and ATP content were observed by overexpression of ADE17, both under control condition and under acetic acid stress, and is consistent with the better growth of the recombinant yeast strain. The global intracellular amino acid profiles were also changed by overexpression of the ADE genes. Among the changed amino acids, significant increase of the stress protectant γ-aminobutyric acid (GABA) was revealed by overexpression of the ADE genes under acetic acid stress, suggesting that overexpression of the ADE genes exerts control on both purine biosynthesis and amino acid biosynthesis to protect yeast cells against the stress. We proved that the de novo purine biosynthesis genes are useful targets for metabolic engineering of yeast stress tolerance. The engineered strains developed in this study with improved tolerance against multiple inhibitors can be employed for efficient lignocellulosic biorefinery to produce biofuels and biochemicals.
TL;DR: The aim of this study was to present well-known yeast species Y. lipolytica as a rare opportunistic fungal pathogen and possible pathogenicity and epidemiology of this yeast species were discussed.
Abstract: Yarrowia lipolytica is one of the most studied "non-conventional" yeast species capable of synthesizing a wide group of valuable metabolites, in particular lipases and other hydrolytic enzymes, microbial oil, citric acid, erythritol and γ-decalactone. Processes based on the yeast have GRAS status ("generally recognized as safe") given by Food and Drug Administration. The majority of research communications regarding to Y. lipolytica claim that the yeast species is non-pathogenic. In spite of that, Y. lipolytica, like other fungal species, can cause infections in immunocompromised and critically ill patients. The yeast possess features that facilitate invasion of the host cell (particularly production of hydrolytic enzymes), as well as the protection of the own cells, such as biofilm formation. The aim of this study was to present well-known yeast species Y. lipolytica as a rare opportunistic fungal pathogen. Possible pathogenicity and epidemiology of this yeast species were discussed. Antifungal drugs susceptibility and increasing resistance to azoles in Y. lipolytica yeasts were also presented.
TL;DR: It is demonstrated that high doses of selenium causes oxidative stress in yeasts, thereby increasing the process of lipid peroxidation inYeasts and encouraging future research on the possibility of a thorough understanding of antioxidant system functioning in yeast cells.
Abstract: Selenium exhibits health-promoting properties in humans and animals. Therefore, the development of selenium-enriched dietary supplements has been growing worldwide. However, it may also exhibit toxicity at higher concentrations, causing increased oxidative stress. Different species of yeasts may exhibit different tolerances toward selenium. Therefore, in this study, we aimed to determine the effect of selenium on growth and on the antioxidative system in Candida utilis ATCC 9950 and Saccharomyces cerevisiae ATCC MYA-2200 yeast cells. The results of this study have demonstrated that high doses of selenium causes oxidative stress in yeasts, thereby increasing the process of lipid peroxidation. In addition, we obtained an increased level of GSSG from aqueous solutions of yeast biomass grown with selenium supplementation (40–60 mg/L). Increased levels of selenium in aqueous solutions resulted in an increase in the activity of antioxidant enzymes, including glutathione peroxidase and glutathione reductase. These results should encourage future research on the possibility of a thorough understanding of antioxidant system functioning in yeast cells.
TL;DR: This study demonstrates the potential of a co-culture of strain LW419a and yeast to rapidly ferment all the sugars in pretreated biomass slurries to ethanol at their respective highest rates.
TL;DR: A sugarcane distillery waste isolate Saccharomyces cerevisiae NGY10 demonstrated high potential for ethanol production, C5 metabolic engineering and developing strategies for SSF, SScF and CBP.
Abstract: Lignocellulosic hydrolysates contain a mixture of hexose (C6)/pentose (C5) sugars and pretreatment-generated inhibitors (furans, weak acids and phenolics). Therefore, robust yeast isolates with characteristics of C6/C5 fermentation and tolerance to pretreatment-derived inhibitors are pre-requisite for efficient lignocellulosic material based biorefineries. Moreover, use of thermotolerant yeast isolates will further reduce cooling cost, contamination during fermentation, and required for developing simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SScF), and consolidated bio-processing (CBP) strategies. In this study, we evaluated thirty-five yeast isolates (belonging to six genera including Saccharomyces, Kluyveromyces, Candida, Scheffersomyces, Ogatea and Wickerhamomyces) for pretreatment-generated inhibitors {furfural, 5-hydroxymethyl furfural (5-HMF) and acetic acid} and thermotolerant phenotypes along with the fermentation performances at 40 °C. Among them, a sugarcane distillery waste isolate, Saccharomyces cerevisiae NGY10 produced maximum 49.77 ± 0.34 g/l and 46.81 ± 21.98 g/l ethanol with the efficiency of 97.39% and 93.54% at 30 °C and 40 °C, respectively, in 24 h using glucose as a carbon source. Furthermore, isolate NGY10 produced 12.25 ± 0.09 g/l and 7.18 ± 0.14 g/l of ethanol with 92.81% and 91.58% efficiency via SHF, and 30.22 g/l and 25.77 g/l ethanol with 86.43% and 73.29% efficiency via SSF using acid- and alkali-pretreated rice straw as carbon sources, respectively, at 40 °C. In addition, isolate NGY10 also produced 92.31 ± 3.39 g/l (11.7% v/v) and 33.66 ± 1.04 g/l (4.26% v/v) ethanol at 40 °C with the yields of 81.49% and 73.87% in the presence of 30% w/v glucose or 4× concentrated acid-pretreated rice straw hydrolysate, respectively. Moreover, isolate NGY10 displayed furfural- (1.5 g/l), 5-HMF (3.0 g/l), acetic acid- (0.2% v/v) and ethanol-(10.0% v/v) tolerant phenotypes. A sugarcane distillery waste isolate NGY10 demonstrated high potential for ethanol production, C5 metabolic engineering and developing strategies for SSF, SScF and CBP.
TL;DR: In this paper, the growth characteristics of probiotic yeast in the presence of wort sugars, ethanol and iso-α-bitter acids were quantified and the highest specific growth rate (μ) was observed on glucose (0.44 ± 0.03 1/h at 30°C), while on maltose and maltotriose it was lower by 34 and 89%, respectively.
Abstract: For brewers, alcohol-free beers (AFBs) are an economically attractive segment of the beer market. At the same time, it is a category of beer that allows breweries to offer innovative products to customers. So far, the use of probiotic yeast in AFB production has not been studied. In this work, the growth characteristics of probiotic yeast in the presence of wort sugars, ethanol and iso-α-bitter acids were quantified. The highest specific growth rate (μ) of probiotic yeast was observed on glucose (0.44 ± 0.03 1/h at 30 °C), while on maltose and maltotriose it was lower by 34 and 89%, respectively. Ethanol (5% v/v) and iso-α-bitter acids (50 IBU) decreased μ on glucose (30 °C) by 20 and 23%, respectively. Response surface methodology was used to identify the main fermentation conditions affecting the formation of esters and higher alcohols. Statistical analysis of the experimental data revealed that the fermentation temperature and pitching rate had the most significant effects on flavour formation. High pressure processing was shown to be a suitable method for inactivating the probiotic yeast.
TL;DR: Microarrays are used to show that TORC1 controls gene expression during steady state growth while PKA speeds up expression changes when nutrient levels change, which may enable yeast to set an exact growth rate based on the abundance of internal metabolites such as amino acids, but also adapt rapidly to changes in external nutrients.
Abstract: The growth rate of a yeast cell is controlled by the target of rapamycin kinase complex I (TORC1) and cAMP-dependent protein kinase (PKA) pathways. To determine how TORC1 and PKA cooperate to regulate cell growth, we performed temporal analysis of gene expression in yeast switched from a non-fermentable substrate, to glucose, in the presence and absence of TORC1 and PKA inhibitors. Quantitative analysis of these data reveals that PKA drives the expression of key cell growth genes during transitions into, and out of, the rapid growth state in glucose, while TORC1 is important for the steady-state expression of the same genes. This circuit design may enable yeast to set an exact growth rate based on the abundance of internal metabolites such as amino acids, via TORC1, but also adapt rapidly to changes in external nutrients, such as glucose, via PKA. Yeast cells respond to nutrients by altering expression of the protein synthesis genes and thus their growth rate. Here, the authors use microarrays to show that TORC1 controls gene expression during steady state growth while PKA speeds up expression changes when nutrient levels change.