Construction of cell factories for production of patchoulol in Saccharomyces cerevisiae / 中国中药杂志

Patchoulol is an important sesquiterpenoid in the volatile oil of Pogostemon cablin, and is also considered to be the main contributing component to the pharmacological efficacy and fragrance of P. cablin oil, which has antibacterial, antitumor, antioxidant, and other biological activities. Currently, patchoulol and its essential oil blends are in high demand worldwide, but the traditional plant extraction method has many problems such as wasting land and polluting the environment. Therefore, there is an urgent need for a new method to produce patchoulol efficiently and at low cost. To broaden the production method of patchouli and achieve the heterologous production of patchoulol in Saccharomyces cerevisiae, the patchoulol synthase(PS) gene from P. cablin was codon optimized and placed under the inducible strong promoter GAL1 to transfer into the yeast platform strain YTT-T5, thereby obtaining strain PS00 with the production of(4.0±0.3) mg·L~(-1) patchoulol. To improve the conversion rate, this study used protein fusion method to fuse SmFPS gene from Salvia miltiorrhiza with PS gene, leading to increase the yield of patchoulol to(100.9±7.4) mg·L~(-1) by 25-folds. By further optimizing the copy number of the fusion gene, the yield of patchoulol was increased by 90% to(191.1±32.7) mg·L~(-1). By optimizing the fermentation process, the strain was able to achieve a patchouli yield of 2.1 g·L~(-1) in a high-density fermentation system, which was the highest yield so far. This study provides an important basis for the green production of patchoulol.

Functional analysis on sucrose transporters in sweet potato / 生物工程学报

Sweet potato is an important food crop that can also be used as an industrial raw material. Sucrose is the main form of long-distance carbohydrate transport in plants, and sucrose transporter (SUT) regulates the transmembrane transport and distribution of sucrose during plant growth and metabolism. Moreover, SUT plays a key role in phloem mediated source-to-sink sucrose transport and physiological activities, supplying sucrose for the sink tissues. In this study, the full-length cDNA sequences of IbSUT62788 and IbSUT81616 were obtained by rapid amplification of cDNA ends (RACE) cloning according to the transcripts of the two SUT coding genes which were differentially expressed in sweet potato storage roots with different starch properties. Phylogenetic analysis was performed to clarify the classification of IbSUT62788 and IbSUT81616. The subcellular localization of IbSUT62788 and IbSUT81616 was determined by transient expression in Nicotiana benthamiana. The function of IbSUT62788 and IbSUT81616 in sucrose and hexose absorption and transport was identified using yeast functional complementarity system. The expression pattern of IbSUT62788 and IbSUT81616 in sweet potato organs were analyzed by real-time fluorescence quantitative PCR (RT-qPCR). Arabidopsis plants heterologous expressing IbSUT62788 and IbSUT81616 genes were obtained using floral dip method. The differences in starch and sugar contents between transgenic and wild-type Arabidopsis were compared. The results showed IbSUT62788 and IbSUT81616 encoded SUT proteins with a length of 505 and 521 amino acids, respectively, and both proteins belonged to the SUT1 subfamily. IbSUT62788 and IbSUT81616 were located in the cell membrane and were able to transport sucrose, glucose and fructose in the yeast system. In addition, IbSUT62788 was also able to transport mannose. The expression of IbSUT62788 was higher in leaves, lateral branches and main stems, and the expression of IbSUT81616 was higher in lateral branches, stems and storage roots. After IbSUT62788 and IbSUT81616 were heterologously expressed in Arabidopsis, the plants grew normally, but the biomass increased. The heterologous expression of IbSUT62788 increased the soluble sugar content, leaf size and 1 000-seed weight of Arabidopsis plants. Heterologous expression of IbSUT81616 increased starch accumulation in leaves and root tips and 1 000-seed weight of seeds, but decreased soluble sugar content. The results obtained in this study showed that IbSUT62788 and IbSUT81616 might be important genes regulating sucrose and sugar content traits in sweet potato. They might carry out physiological functions on cell membrane, such as transmembrane transport of sucrose, sucrose into and out of sink tissue, as well as transport and unloading of sucrose into phloem. The changes in traits result from their heterologous expression in Arabidopsis indicates their potential in improving the yield of other plants or crops. The results obtained in this study provide important information for revealing the functions of IbSUT62788 and IbSUT81616 in starch and glucose metabolism and formation mechanism of important quality traits in sweet potato.

Advances in the production of chemicals by organelle compartmentalization in Saccharomyces cerevisiae / 生物工程学报

As a generally-recognized-as-safe microorganism, Saccharomyces cerevisiae is a widely studied chassis cell for the production of high-value or bulk chemicals in the field of synthetic biology. In recent years, a large number of synthesis pathways of chemicals have been established and optimized in S. cerevisiae by various metabolic engineering strategies, and the production of some chemicals have shown the potential of commercialization. As a eukaryote, S. cerevisiae has a complete inner membrane system and complex organelle compartments, and these compartments generally have higher concentrations of the precursor substrates (such as acetyl-CoA in mitochondria), or have sufficient enzymes, cofactors and energy which are required for the synthesis of some chemicals. These features may provide a more suitable physical and chemical environment for the biosynthesis of the targeted chemicals. However, the structural features of different organelles hinder the synthesis of specific chemicals. In order to ameliorate the efficiency of product biosynthesis, researchers have carried out a number of targeted modifications to the organelles grounded on an in-depth analysis of the characteristics of different organelles and the suitability of the production of target chemicals biosynthesis pathway to the organelles. In this review, the reconstruction and optimization of the biosynthesis pathways for production of chemicals by organelle mitochondria, peroxisome, golgi apparatus, endoplasmic reticulum, lipid droplets and vacuole compartmentalization in S. cerevisiae are reviewed in-depth. Current difficulties, challenges and future perspectives are highlighted.

Advances on the production of organic acids by yeast / 生物工程学报

Organic acids are organic compounds that can be synthesized using biological systems. They often contain one or more low molecular weight acidic groups, such as carboxyl group and sulphonic group. Organic acids are widely used in food, agriculture, medicine, bio-based materials industry and other fields. Yeast has unique advantages of biosafety, strong stress resistance, wide substrate spectrum, convenient genetic transformation, and mature large-scale culture technology. Therefore, it is appealing to produce organic acids by yeast. However, challenges such as low concentration, many by-products and low fermentation efficiency still exist. With the development of yeast metabolic engineering and synthetic biology technology, rapid progress has been made in this field recently. Here we summarize the progress of biosynthesis of 11 organic acids by yeast. These organic acids include bulk carboxylic acids and high-value organic acids that can be produced naturally or heterologously. Finally, future prospects in this field were proposed.

Homeopathy on cultures of Saccharomyces cerevisiaeand impact on fermentation

Studies have shownthat homeopathy modulates the activity of both single-and multi-celled organisms;therefore, we propose a study into the action of Arnica Montanaand S. cerevisiae fungus nosode on growth "in vitro", and on the fermentation of S. cerevisiaeon brewer's wort. Methods:250 µL of medication in 30% alcohol were placed in 5 mL of Sabouraud Broth (SB) or wort, with 20 µL of fungus ata McFarland standard of 0.5 and in a dilution of 1:100. Fungal growth was evaluated via spectrophotometry at 600 nm or a cell count in a Neubauer chamber in a kinetic of 1 to 5 days' incubation at 25ºC. The production of alcohol by the fungus was evaluated using the BRIX index in the samekinetic. 1x107fungi/mL were previously incubated with medication for 5 days and, afterwards, placed in 20 mL of fresh wort, incubated at 25ºC for 7 days and evaluated for growth and sugar consumption. Resultsand Discussion: The SB results revealed that after 2days incubation with Arnica30CH, an increase in fungal growth was observed (p<0.0001), whilewith nosode 6 and 30CH there was a reduction in growth after 2 and 5 days incubation (p<0.001). The fungi incubated with Arnica30CH exhibited increased sugar consumption after 2 and5 days incubation (p<0.05), while the nosode 30CH resulted in lower sugar consumption after 2 and 3 days incubation (p<0.05). The results for fungal growth and sugar consumption with the wort were similar to those using SB.The fungalcultures previously incubated with homeopathic medication and subsequent incubation with fresh wortindicated a loss of distinction, bothin terms of fungal growth and sugar consumption. This piece of data may suggest action by the homeopathic medication only when in contact with the cells. Conclusion: The treatment of the S. cerevisiae fungus using Arnica and the S. cerevisiae nosode produced a significant modulation in fungal growth and sugar consumption.

Dynamic control of ERG20 expression to improve production of monoterpenes by engineering Saccharomyces cerevisiae / 中国中药杂志

Monoterpenes are widely used in cosmetics, food, medicine, agriculture and other fields. With the development of synthetic biology, it is considered as a potential way to create microbial cell factories to produce monoterpenes. Engineering Saccharomyces cerevisiae to produce monoterpenes has been a research hotspot in synthetic biology. In S. cerevisiae, the production of geranyl pyrophosphate(GPP) and farnesyl pyrophosphate(FPP) is catalyzed by a bifunctional enzyme farnesyl pyrophosphate synthetase(encoded by ERG20 gene) which is inclined to synthesize FPP essential for yeast growth. Therefore, reasonable control of FPP synthesis is the basis for efficient monoterpene synthesis in yeast cell factories. In order to achieve dynamic control from GPP to FPP biosynthesis in S. cerevisiae, we obtained a novel chassis strain HP001-pERG1-ERG20 by replacing the ERG20 promoter of the chassis strain HP001 with the promoter of cyclosqualene cyclase(ERG1) gene. Further, we reconstructed the metabolic pathway by using GPP and neryl diphosphate(NPP), cis-GPP as substrates in HP001-pERG1-ERG20. The yield of GPP-derived linalool increased by 42.5% to 7.6 mg·L~(-1), and that of NPP-derived nerol increased by 1 436.4% to 8.3 mg·L~(-1). This study provides a basis for the production of monoterpenes by microbial fermentation.

Identification and verification of key salt-tolerant amino acid sites of banana MaNHX5 / 生物工程学报

In order to improve the salt tolerance of banana NHX genes, we cloned a MaNHX5 gene from Musa acuminata L. AAA group and predicted the key salt-tolerant amino acid sites and mutant protein structure changes of MaNHX5 by using bioinformatics tools. The 276-position serine (S) of MaNHX5 protein was successfully mutated to aspartic acid (D) by site-directed mutagenesis, and the AXT3 salt-sensitive mutant yeast was used for a functional complementation test. The results showed that after the mutated MaNHX5 gene was transferred to AXT3 salt-sensitive mutant yeast, the salt tolerance of the mutant yeast was significantly improved under 200 mmol/L NaCl treatment. It is hypothesized that Ser276 of MaNHX5 protein plays an important role in the transport of Na+ across the tonoplast.

N-terminal truncation of prenyltransferase enhances the biosynthesis of prenylnaringenin / 生物工程学报

8-prenylnaringenin (8-PN) is a potent estrogen with high medicinal values. It also serves as an important precursor for many prenylated flavonoids. Microbial synthesis of 8-PN is mainly hindered by the low catalytic activity of prenyltransferases (PTS) and insufficient supply of precursors. In this work, a SfN8DT-1 from Sophora flavescens was used to improve the efficiency of (2S)-naringenin prenylation. The predicted structure of SfN8DT-1 showed that its main body is comprised of 9 α-helices and 8 loops, along with a long side chain formed by nearly 120 amino acids. SfN8DT-1 mutants with different side-chain truncated were tested in Saccharomyces cerevisiae. A mutant expressing the truncated enzyme at K62 site, designated as SfND8T-1-t62, produced the highest 8-PN titer. Molecular docking of SfN8DT-1-t62 with (2S)-naringenin and dimethylallyl diphosphate (DMAPP) showed that K185 was a potentially crucial residue. Alanine scanning within a range of 0.5 nm around these two substrates showed that the mutant K185A may decrease its affinity to substrates, which also indicated K185 was a potentially critical residue. Besides, the mutant K185W enhanced the affinity to ligands implied by the simulated saturation mutation, while the saturated mutation of K185 showed a great decrease in 8-PN production, indicating K185 is vital for the activity of SfN8DT-1. Subsequently, overexpressing the key genes of Mevalonate (MVA) pathway further improved the titer of 8-PN to 31.31 mg/L, which indicated that DMAPP supply is also a limiting factor for 8-PN synthesis. Finally, 44.92 mg/L of 8-PN was produced in a 5 L bioreactor after 120 h, which is the highest 8-PN titer reported to date.

URA3 affects artemisinic acid production by an engineered Saccharomyces cerevisiae in pilot-scale fermentation / 生物工程学报

CRISPR/Cas9 has been widely used in engineering Saccharomyces cerevisiae for gene insertion, replacement and deletion due to its simplicity and high efficiency. The selectable markers of CRISPR/Cas9 systems are particularly useful for genome editing and Cas9-plasmids removing in yeast. In our previous research, GAL80 gene has been deleted by the plasmid pML104-mediated CRISPR/Cas9 system in an engineered yeast, in order to eliminate the requirement of galactose supplementation for induction. The maximum artemisinic acid production by engineered S. cerevisiae 1211-2 (740 mg/L) was comparable to that of the parental strain 1211 without galactose induction. Unfortunately, S. cerevisiae 1211-2 was inefficient in the utilization of the carbon source ethanol in the subsequent 50 L pilot fermentation experiment. The artemisinic acid yield in the engineered S. cerevisiae 1211-2 was only 20%-25% compared with that of S. cerevisiae 1211. The mutation of the selection marker URA3 was supposed to affect the growth and artemisinic acid production. A ura3 mutant was successfully restored by a recombinant plasmid pML104-KanMx4-u along with a 90 bp donor DNA, resulting in S. cerevisiae 1211-3. This mutant could grow normally in a fed-batch fermentor with mixed glucose and ethanol feeding, and the final artemisinic acid yield (> 20 g/L) was comparable to that of the parental strain S. cerevisiae 1211. In this study, an engineered yeast strain producing artemisinic acid without galactose induction was obtained. More importantly, it was the first report showing that the auxotrophic marker URA3 significantly affected artemisinic acid production in a pilot-scale fermentation with ethanol feeding, which provides a reference for the production of other natural products in yeast chassis.

Engineering Saccharomyces cerevisiae for efficient production of glucaric acid / 生物工程学报

As an important dicarboxylic acids existing in nature, glucaric acid has been widely used in medical, health, and polymer materials industry, therefore it is considered as one of the "top value-added chemicals from biomass". In this study, using Saccharomyces cerevisiae as a chassis microorganism, the effects of overexpression of myo-inositol transporter Itr1, fusional expression of inositol oxygenase MIOX4 and uronate dehydrogenase Udh, and down-expression of glucose-6-phosphate dehydrogenase gene ZWF1 on the glucaric acid production were investigated. The results showed that the yield of glucaric acid was increased by 26% compared with the original strain Bga-3 under shake flask fermentation after overexpressing myo-inositol transporter Itr1. The yield of glucaric acid was increased by 40% compared with Bga-3 strain by expressing the MIOX4-Udh fusion protein. On these basis, the production of glucaric acid reached 5.5 g/L, which was 60% higher than that of Bga-3 strain. In a 5 L fermenter, the highest yield of glucaric acid was 10.85 g/L, which was increased 80% compared with that of Bga-3 strain. The application of the above metabolic engineering strategy improved the pathway efficiency and the yield of glucaric acid, which may serve as a reference for engineering S. cerevisiae to produce other chemicals.

Effect of key enzymes ubiquitination sites on the biosynthesis of naringenin / 生物工程学报

Flavonoids have a variety of biological activities and have important applications in food, medicine, cosmetics, and many other fields. Naringenin is a platform chemical for the biosynthesis of many important flavonoids. Ubiquitination plays a pivotal role in the post-translational modification of proteins and participates in the regulation of cellular activities. Ubiquitinated proteins can be degraded by the ubiquitin-protease system, which is important for maintaining the physiological activities of cells, and may also exert a significant impact on the expression of exogenous proteins. In this study, a real-time in-situ detection system for ubiquitination modification has been established in Saccharomyces cerevisiae by using a fluorescence bimolecular complementation approach. The ubiquitination level of protein was characterized by fluorescence intensity. By using the approach, the potential ubiquitination sites of proteins involved in the naringenin biosynthesis pathway have been obtained. The lysine residues of the relevant ubiquitination sites were mutated to arginine to reduce the ubiquitination level. The mutants of tyrosine ammonia-lyase (FjTAL) and chalcone synthase (SjCHS, SmCHS) showed decreased fluorescence, suggested that a decreased ubiquitination level. After fermentation verification, the S. cerevisiae expressing tyrosine ammonia-lyase FjTAL mutant FjTAL-K487R accumulated 74.2 mg/L p-coumaric acid at 72 h, which was 32.3% higher than that of the original FjTAL. The strains expressing chalcone synthase mutants showed no significant change in the titer of naringenin. The results showed that mutation of the potential ubiquitination sites of proteins involved in the naringenin biosynthesis pathway could increase the titer of p-coumaric acid and have positive effect on naringenin biosynthesis.

Higher alcohols metabolism by Saccharomyces cerevisiae: a mini review / 生物工程学报

Higher alcohols are one of the main by-products of Saccharomyces cerevisiae in brewing. High concentration of higher alcohols in alcoholic beverages easily causes headache, thirst and other symptoms after drinking. It is also the main reason for chronic drunkenness and difficulty in sobering up after intoxication. The main objective of this review is to present an overview of the flavor characteristics and metabolic pathways of higher alcohols as well as the application of mutagenesis breeding techniques in the regulation of higher alcohol metabolism in S. cerevisiae. In particular, we review the application of metabolic engineering technology in genetic modification of amino transferase, α-keto acid metabolism, acetate metabolism and carbon-nitrogen metabolism. Moreover, key challenges and future perspectives of realizing optimization of higher alcohols metabolism are discussed. This review is intended to provide a comprehensive understanding of metabolic regulation system of higher alcohols in S. cerevisiae and to provide insights into the rational development of the excellent industrial S. cerevisiae strains producing higher alcohols.

Effect of RIM21 gene disruption on flocculation of lager yeast / 生物工程学报

Lager yeast is the most popular yeast strain used for beer production in China. The flocculation of yeast plays an important role in cell separation at the end of fermentation. Therefore, appropriately enhancing the flocculation capability of the lager yeast without affecting its fermentation performance would be desirable for beer industry. Our previous study showed that the defect of gene RIM21 might contribute to the enhanced flocculation capability of a lager yeast G03. To further investigate the role of the RIM21 gene in flocculation of strain G03, this study constructed a RIM21-deleted mutant strain G03-RIM21Δ through homologous recombination. Deletion of RIM21 improved the flocculation capability of strain G03 during wort fermentation at 11 °C without changing its fermentation performance significantly. The expression of FLO5, Lg-FLO1 and some other genes involved in cell wall integrity pathway were up-regulated in strain G03-RIM21Δ. In addition, the disruption of RIM21 enhanced resistance of yeast cells to cell wall inhibitors. These results provide a basis for elucidating the flocculation mechanism of lager yeast under low-temperature fermentation conditions.

Overexpression of a leucine transfer RNA gene tL(CAA)K improves the acetic acid tolerance of Saccharomyces cerevisiae / 生物工程学报

Acetic acid is a common inhibitor present in lignocellulosic hydrolysate. Development of acetic acid tolerant strains may improve the production of biofuels and bio-based chemicals using lignocellulosic biomass as raw materials. Current studies on stress tolerance of yeast Saccharomyces cerevisiae have mainly focused on transcription control, but the role of transfer RNA (tRNA) was rarely investigated. We found that some tRNA genes showed elevated transcription levels in a stress tolerant yeast strain. In this study, we further investigated the effects of overexpressing an arginine transfer RNA gene tR(ACG)D and a leucine transfer RNA gene tL(CAA)K on cell growth and ethanol production of S. cerevisiae BY4741 under acetic acid stress. The tL(CAA)K overexpression strain showed a better growth and a 29.41% higher ethanol productivity than that of the control strain. However, overexpression of tR(ACG)D showed negative influence on cell growth and ethanol production. Further studies revealed that the transcriptional levels of HAA1, MSN2, and MSN4, which encode transcription regulators related to stress tolerance, were up-regulated in tL(CAA)K overexpressed strain. This study provides an alternative strategy to develop robust yeast strains for cellulosic biorefinery, and also provides a basis for investigating how yeast stress tolerance is regulated by tRNA genes.

Enhancement of ethanol production efficiency in repeated-batch fermentation from sweet sorghum stem juice: effect of initial sugar, nitrogen and aeration

BACKGROUND: Ethanol concentration (PE), ethanol productivity (QP) and sugar consumption (SC) are important values in industrial ethanol production. In this study, initial sugar and nitrogen (urea) concentrations in sweet sorghum stem juice (SSJ) were optimized for high PE (≥10%, v/v), QP, (≥2.5 g/L·h) and SC (≥90%) by Saccharomyces cerevisiae SSJKKU01. Then, repeated-batch fermentations under normal gravity (NG) and high gravity (HG) conditions were studied. RESULTS: The initial sugar at 208 g/L and urea at 2.75 g/L were the optimum values to meet the criteria. At the initial yeast cell concentration of ~1 × 108 cells/mL, the PE, QP and SC were 97.06 g/L, 3.24 g/L·h and 95.43%, respectively. Repeated-batch fermentations showed that the ethanol production efficiency of eight successive cycles with and without aeration were not significantly different when the initial sugar of cycles 2 to 8 was under NG conditions (~140 g/L). Positive effects of aeration were observed when the initial sugar from cycle 2 was under HG conditions (180­200 g/L). The PE and QP under no aeration were consecutively lower from cycle 1 to cycle 6. Additionally, aeration affected ergosterol formation in yeast cell membrane at high ethanol concentrations, whereas trehalose content under all conditions was not different. CONCLUSION: Initial sugar, sufficient nitrogen and appropriated aeration are necessary for promoting yeast growth and ethanol fermentation. The SSJ was successfully used as an ethanol production medium for a high level of ethanol production. Aeration was not essential for repeated-batch fermentation under NG conditions, but it was beneficial under HG conditions.

Disentangling the genetic bases of Saccharomyces cerevisiae nitrogen consumption and adaptation to low nitrogen environments in wine fermentation

The budding yeast Saccharomyces cerevisiae has been considered for more than 20 years as a premier model organ- ism for biological sciences, also being the main microorganism used in wide industrial applications, like alcoholic fermentation in the winemaking process. Grape juice is a challenging environment for S. cerevisiae , with nitrogen deficiencies impairing fermentation rate and yeast biomass production, causing stuck or sluggish fermentations, thus generating sizeable economic losses for wine industry. In the present review, we summarize some recent efforts in the search of causative genes that account for yeast adaptation to low nitrogen environments, specially focused in wine fermentation conditions. We start presenting a brief perspective of yeast nitrogen utilization under wine fermentative conditions, highlighting yeast preference for some nitrogen sources above others. Then, we give an outlook of S. cerevisiae genetic diversity studies, paying special attention to efforts in genome sequencing for population structure determination and presenting QTL mapping as a powerful tool for phenotype-genotype correlations. Finally, we do a recapitulation of S. cerevisiae natural diversity related to low nitrogen adaptation, specially showing how different studies have left in evidence the central role of the TORC1 signalling pathway in nitrogen utilization and positioned wild S. cerevisiae strains as a reservoir of beneficial alleles with potential industrial applications (e.g. improvement of industrial yeasts for wine production). More studies focused in disentangling the genetic bases of S. cerevisiae adaptation in wine fermentation will be key to determine the domestication effects over low nitrogen adaptation, as well as to definitely proof that wild S. cerevisiae strains have potential genetic determinants for better adaptation to low nitrogen conditions.

Bioremediation of heavy metals in food industry: application of Saccharomyces cerevisiae

Heavy metals are natural elements in the Earth's crust that can enter human food through industrial or agricultural processing, in the form of fertilizers and pesticides. These elements are not biodegradable. Some heavy metals are known as pollutants and are toxic, and their bioaccumulation in plant and animal tissues can cause undesirable effects for humans; therefore, their amount in water and food should always be under control. The aim of this study is to investigate the conditions for the bioremediation of heavy metals in foods. Various physical, chemical, and biological methods have been used to reduce the heavy metal content in the environment. During the last decades, bioremediation methods using plants and microorganisms have created interest to researchers for their advantages such as being more specific and environmentally friendly. The main pollutant elements in foods and beverages are lead, cadmium, arsenic, and mercury, which have their own permissible limits. Among the microorganisms that are capable of bioremediation of heavy metals, Saccharomyces cerevisiae is an interesting choice for its special characteristics and being safe for humans, which make it quite common and useful in the food industry. Its mass production as the byproduct of the fermentation industry and the low cost of culture media are the other advantages. The ability of this yeast to remove an individual separated element has also been widely investigated. In countries with high heavy metal pollution in wheat, the use of S. cerevisiae is a native solution for overcoming the problem of solution. This article summarizes the main conditions for heavy metal absorption by S. cerevisiae.

Effective diffusion coefficients and bioconversion rates of inhibitory compounds in flocs of Saccharomyces cerevisiae

Background: Fermentation strategies for bioethanol production that use flocculating Saccharomyces cerevisiae yeast need to account for the mechanism by which inhibitory compounds, generated in the hydrolysis of lignocellulosic materials, are tolerated and detoxified by a yeast floc. Results: Diffusion coefficients and first-order kinetic bioconversion rate coefficients were measured for three fermentation inhibitory compounds (furfural, hydroxymethylfurfural, and vanillin) in self-aggregated flocs of S. cerevisiae NRRL Y-265. Thièle-type moduli and internal effectiveness factors were obtained by simulating a simple steady-state spherical floc model. Conclusions: The obtained values for the Thiéle moduli and internal effectiveness factors showed that the bioconversion rate of the inhibitory compounds is the dominant phenomenon over mass transfer inside the flocs.

Saccharomyces cerevisiae populations and other yeasts associated with indigenous beers (chicha) of Ecuador

ABSTRACT Chicha, a type of beer made mainly with maize or cassava, is a traditional fermented beverage of the Andean region. There have only been a few studies on yeasts associated with chicha fermentation, and the species diversity occurring during the production of this beverage is not known. The objective of this study was to determine the biodiversity of yeasts in chicha, and to characterize the Saccharomyces cerevisiae populations associated with the production of chicha de jora, seven-grain chicha, chicha de yuca, and chicha de morocho in Ecuador. The molecular diversity of S. cerevisiae populations was determined by restriction polymorphism mitochondrial profiles. The beverages were characterized based on their physicochemical parameters. Twenty-six species were identified, and the most prevalent species were S. cerevisiae and Torulaspora delbrueckii. Other yeast species were isolated at low frequencies. Among 121 isolates of S. cerevisiae, 68 different mtDNA molecular profiles were identified. These results showed that chichas are fermented by a high number of different strains of S. cerevisiae. Some other species provided a minor contribution to the fermentation process. The chicha presented generally similar physicochemical parameters to those observed for other traditional fermented beverages, and can be considered as an acid fermented beverage.

Síntesis y regulación de compuestos del aroma y el sabor derivados de la levadura en la cerveza: ásteres / Synthesis and regulation of flavor compounds derived from brewing yeast: Esters

Las levaduras, durante el proceso de elaboración de cerveza, producen más de 500 compuestos químicos; estos pueden impactar tanto negativa como positivamente en las características organolépticas de la cerveza. En los últimos años, y en particular gracias al avance de la biología molecular y la genómica, se han logrado progresos notables en el conocimiento de las bases moleculares y celulares de la síntesis y regulación de muchos de estos compuestos que inciden en lo que se denomina flavor (aroma y sabor) de la cerveza. Este artículo está enfocado en los ésteres responsables del aroma y el sabor floral y frutado de la cerveza. La formación de estos ésteres depende de diversas enzimas y de factores como la concentración de nutrientes presente en el mosto, la cantidad de oxígeno y dióxido de carbono disuelto, la temperatura de fermentación y, principalmente, la genética de la levadura utilizada. En esta revisión se brinda información de cómo se originan los ésteres y cómo los diferentes parámetros fermentativos impactan en las concentraciones finales de estos compuestos y en la calidad del producto terminado.

During brewing process yeast produce more than 500 chemical compounds that can negatively and positively impact beer at the organoleptic level. In recent years, and particularly thanks to the advancement of molecular biology and genomics, there has been considerable progress in our understanding about the molecular and cellular basis of the synthesis and regulation of many of these flavor compounds. This article focuses on esters, responsible for the floral and fruity beer flavor. Its formation depends on various enzymes and factors such as the concentration of wort nutrients, the amount of dissolved oxygen and carbon dioxide, fermentation temperature and mainly the genetics of the yeast used. We provide information about how the esters originate and how is the impact of different fermentative parameters on the final concentrations of these compounds and the quality of the end product.