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PubMed1996

Evaluating the efficacy of selenium-enriched yeast and sodium selenite on tissue selenium retention and serum glutathione peroxidase activity in grower and finisher swine.

Three experiments conducted with grower-finisher pigs evaluated sodium selenite and a Se-enriched yeast source at various dietary Se levels on Se retention, tissue and serum Se concentrations, and serum glutathione peroxidase (GSH-Px) activity. Experiment 1 was a balance trial conducted in a 2 x 3 factorial arrangement in a randomized complete block (RCB) design in six replicates. Both Se sources were added at .1, .3, or .5 ppm Se. Crossbred barrows (n = 36) averaging 35.9 kg BW were placed in individual metabolism crates and fed their treatment diets, with feces and urine collected for a 7-d test period. Selenium retention increased as dietary Se levels increased, particularly when the Se-enriched yeast was provided, resulting in a Se source x Se level interaction (P < .01). As dietary Se levels increased, urinary Se increased more when pigs were fed sodium selenite, whereas fecal Se increased more when the Se-enriched yeast was fed; both excretion routes resulting in Se level x Se source interaction responses (P < .01). Experiments 2 and 3 were conducted as RCB involving grower (n = 210) and finisher (n = 266) pigs, respectively, and evaluated the two Se sources each at .1, .3, or .5 ppm Se with a non-Se-fortified basal diet serving as a negative control. In Exp. 2, pigs were fed their treatment diets from 22.2 to 60 kg BW in five replicates, whereas in Exp. 3 diets were fed from 65.8 to 105 kg BW in six replicates. Grower pigs fed sodium selenite had serum GSH-Px activity that reached a plateau at .1 ppm Se and .3 ppm when the Se-enriched yeast source was fed, but the interaction response was not significant (P < .15). During the finisher period, serum GSH-Px activity reached a plateau at .1 ppm Se for both Se sources. Serum Se concentrations were lower at .1 ppm Se when the Se-enriched yeast source was fed, resulting in a source x level interaction response for both grower (P < .05) and finisher (P < .01) periods. Loin Se contents were higher in grower and finisher pigs as dietary Se levels increased when the Se-enriched yeast was fed, resulting in a Se source x Se level interaction (P < .01). The results suggest that more Se was retained in muscle tissue when the Se-enriched yeast source was fed, that serum GSH-Px activity reached a plateau at approximately .1 ppm Se, and that sodium selenite may be more biologically available for GSH-Px activity than the Se-enriched yeast source.

Animals↗
PubMed1993

Yeast extracellular proteases.

Many species of yeast secrete significant amounts of protease(s). In this article, results of numerous surveys of yeast extracellular protease production have been compiled and inconsistencies in the data and limitations of the methodology have been examined. Regulation, purification, characterization, and processing of yeast extracellular proteases are reviewed. Results obtained from the sequences of cloned genes, especially the Saccharomyces cerevisiae Bar protease, the Candida albicans acid protease, and the Yarrowia lipolytica alkaline protease, have been emphasized. Biotechnological applications and the medical relevance of yeast extracellular proteases are covered. Yeast extracellular proteases have potential in beer and wine stabilization, and they probably contribute to pathogenicity of Candida spp. Yeast extracellular protease genes also provide secretion and processing signals for yeast expression systems designed for secretion of heterologous proteins. Coverage of the secretion of foreign proteases such as prochymosin, urokinase, and tissue plasminogen activator by yeast in included.

Amino Acid Sequence↗
PubMed1979

Reduction of hepatic lipid deposition in laying hens by dietary selenium-yeast interaction.

Experiments were conducted to study the effect of chromiun and selenium on liver lipid deposition and incidence of liver hemorrhage in caged layers. Commercial strains of layers were fed ad libitum equicaloric and isonitrogenous diets. Corn-torula dried yeast diets containing added selenium (.1 microgram/g) with or without supplementary chromium (10 microgram/g) significantly reduced total liver lipid and liver hemorrhage. The effects of protein source (soybean meal vs. yeast) and selenium were separated in a factorial experiment which showed that the hepatic lipid response to selenium results from an interaction of selenium with an unidentified factor in torula yeast. The addition of selenium to diets with each protein source significantly elevated glutathione peroxidase (GSHPx) activity. Inclusion of 5% brewers yeast in the corn-soy diet or vitamin E (50 IU/kg) to the corn-torula dried yeast reduced liver lipid similar to that seen in birds fed the torula-yeast diet containing .1 microgram Se/g. Comparison of oral glucose tolerance of birds fed corn-soy and corn-soy brewers yeast diets showed no significant difference. None of the dietary treatments significantly altered body weight, egg production, egg weight, or feed consumption. The results indicate that the metabolic role of selenium in relation to its role in hepatic lipid metabolism is mediated through an interaction with a dietary factor(s) present in yeast.

Animal Feed↗
PubMed1999

[Establishment of mouse p53 yeast functional assay and evaluation of its detectability of p53 gene mutation].

Mice have widely been used as an experimental model for carcinogenesis induced by chemicals or irradiation. Recently, transgenic mice expressing oncogene proteins and knockout mice lacking for tumor suppressor genes are available, and used for the analysis of mechanisms underlying carcinogenesis. In such experimental carcinogenesis, a rapid and sensitive method for screening p53 mutations is desired. In human carcinogenesis, p53 yeast functional assay has been proved to be a very useful method for screening p53 mutations. However, the p53 yeast functional assay has been unsuccessful in mice because of the high background mutations in them. In the present study, the author developed a mouse p53 yeast functional assay by reducing the background mutations. Initially, 25.8 +/- 2.8% of background mutant red colonies were given by total RNA from normal mouse liver. The background level was lowered to 13.6 +/- 3.3% by improvement of RT-PCR conditions. Then the p53 cDNA-containing plasmids were rescued from the red colonies and the cDNA sequences were determined. The analysis revealed that many background mutations were caused by insertions of extra adenine (A) and thymine (T) at A and T homopolymeric runs, respectively. Majority of the insertion mutations occurred at 5' terminus of murine p53 cDNA. Based on these findings, we constructed a new vector and designed an optimal PCR primer set to exclude 5' terminal sequence in the yeast assay. Finally, the background mutation rate was reduced to 8.0 +/- 1.4%, which was comparable with the rate of 5.2 +/- 2.7% in human p53 yeast functional assay. Using the murine p53 yeast functional assay, we screened several cell lines for p53 mutations and determined those mutations by DNA sequencing. Furthermore, we investigated p53 mutations in UV-irradiated skins of XPC-gene-knockout mice. The yeast functional assay followed by DNA sequencing analysis revealed predominant mutations in dipyrimidines in the p53 coding sequence. These results indicate that mouse p53 yeast functional assay will be very useful for the analysis of p53 mutations in experimental carcinogenesis.

Animals↗
PubMed2002

[Transcriptional activation function of hepatitis B virus Pre S1 protein in yeast].

BACKGROUND: To explore the feasibility of cloning of the hepatocyte receptor interacting with the Pre S1 protein of HBV by two hybrid system. METHODS: Yeast expression plasmids encoding fusion proteins of full length or portions of Pre S1 of HBV and DNA binding domain of yeast protein GAL4 were constructed and used to transform yeast reporter strain SFY526. Reporter gene product ?galactosidase activity was assayed as a measure of transcription activation in yeast. Mammalian expression plasmid encoding fusion proteins of full length Pre S1 and DNA binding domain of GAL4 was constructed and used to cotransfect hepatoma cell line Huh?7 together with CAT reporter plasmid. Cell extracts were assayed for CAT activity by thin?layer chromatography. RESULTS: The fusion proteins of full length Pre S1 protein and GAL4 DNA binding domain present transcriptional activation function in yeast. The transcription activating sequence is localized to the 21 to 47 amino acids of Pre S1 protein Fusion proteins of full length Pre S 1 and GAL 4 DNA binding domain do not show transcriptional activation function in mammalian cells. CONCLUSION: The transcriptional activating sequence of HBVPre S1 protein in yeast overlaps the hepatocyte receptor binding site. The transcriptional activation function of HBV Pre S1 protein in yeast may prevent researchers?from using yeast two hybrid system to clone HBV receptor interacting with Pre S1 protein. However, the Pre S1 protein does not show transcriptional activation function in mammalian cells. Mammalian two?hybrid system may be a practical method to clone the HBV hepatocyte receptor interacting with Pre S1 protein.

DNA-Binding Proteins↗
PubMedDate not supplied

[Selenium tolerance of yeasts].

Selenium tolerance of yeasts widely varies: the growth of some yeasts can be inhibited by a selenium concentration as low as 10(-4) M, whereas others can grow in the presence of 10(-1) M selenium. Homogeneous yeast taxa are characterized by a certain level of selenium tolerance, and heterogeneous taxa show a variable level of tolerance to selenium. In general, ascomycetous yeasts are more tolerant to selenium than basidiomycetous yeasts. Among the ascomycetous yeasts, the genera Dekkera and Schizosaccharomyces exhibited the lowest and the species Candida maltosa, Hanseniaspora valbyensis, Kluyveromyces marxianus, and Yarrowia lipolytica the highest tolerance to selenium. Among the basidiomycetous yeasts, the genera Bullera, Cryptococcus, and Holtermannia showed the lowest and the species Cryptococcus curvatus, Cr. humicola, and Trichosporon spp. the highest tolerance to selenium. The selenium tolerance of yeasts depends on the composition of the growth medium, in particular, on the presence of sulfate, sulfur-containing amino acids, and glutamine in the medium.

Adaptation, Physiological↗
PubMed2003

Transcriptional activation function of hepatitis B virus Pre S1 protein in yeast.

OBJECTIVE: To explore the feasibility of cloning of the hepatocyte receptor interacting with the Pre S1 protein of HBV by two-hybrid system. METHODS: Yeast expression plasmids encoding fusion proteins of full length or portions of Pre S1 of HBV and DNA binding domain of yeast protein GAL4 were constructed and used to transform yeast reporter strain SFY526. Reporter gene product beta-galactosidase activity was assayed as a measure of transcriptional activation in yeast. Mammalian expression plasmid encoding fusion proteins of full length Pre S1 and DNA binding domain of GAL4 was constructed and used to cotransfect hepatoma cell line Huh-7 together with CAT reporter plasmid. Cell extracts were assayed for CAT activity by thin-layer chromatography. RESULTS: The fusion proteins of full length Pre S1 protein and GAL4 DNA binding domain presented transcriptional activation function in yeast. The transcription activating sequence was localized to the 21 to 47 amino acids of Pre S1 protein. Fusion proteins of full length Pre S1 and GAL4 DNA binding domain did not show transcriptional activation function in mammalian cells. CONCLUSIONS: The transcription activating sequence of HBV Pre S1 protein in yeast overlaps the hepatocyte receptor binding site. The transcriptional activation function of HBV Pre S1 protein in yeast may prevent researchers from using yeast two-hybrid system to clone HBV receptor interacting with Pre S1 protein. However, the Pre S1 protein does not show transcriptional activation function in mammalian cells. Mammalian two-hybrid system may be a practical method to clone the HBV hepatocyte receptor interacting with Pre S1 protein.

Animals↗
PubMed2002

Cloning and expression of the gene of augmenter of liver regeneration in yeast cells.

OBJECTIVE: To study the function of augmenter of liver regeneration (ALR) as a regulatory factor that specifically stimulates hepatic cell regeneration, we constructed yeast expressive vector of ALR and expressed it in yeast cells. METHODS: Total RNA was extracted from HepG2 cells, and reverse transcription polymerase chain reaction (RT-PCR) was performed to amplify the coding region of ALR. The products were cloned into PGEM-T vector and sequenced, then cloned into PGBK T7 vector. The recombinant plasmid PGBK T7-ALR was transformed into yeast AH109. The yeast protein was extracted and analyzed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting hybridization technique. RESULTS: DNA sequencing results confirmed that the coding region of ALR was correctly inserted into the yeast expression vector, and Western blotting assay showed that recombinant ALR was successfully expressed in yeast. Its molecular weight was identical to the theoretical value of 15 000 Da; the protein was found inside the yeast cells. CONCLUSION: The successful expression of ALR in yeast cells makes it possible to study further on its biological function.

Blotting, Western↗
PubMedDate not supplied

[Groups and sources of yeasts in house dust].

House dust contains bacteria, mycelial fungi, microarthropods, and yeasts. The house dust samples collected in 25 apartments in Moscow and the Moscow region were found to contain yeasts belonging to the genera Candida, Cryptococcus, Debaryomyces, Rhodotorula, Sporobolomyces, and Trichosporon. The most frequently encountered microorganisms were typical epiphytic yeasts, such as Cryptococcus diffluens and Rhodotorula mucilaginosa, which are capable of long-term preservation in an inactive state. The direct source of epiphytic yeasts occurring in the house dust might be the indoor plants, which were contaminated with these yeasts, albeit to a lesser degree than outdoor plants. Along with the typical epiphytic yeasts, the house dust contained the opportunistic yeast pathogens Candida catenulata, C. guillermondii, C. haemulonii, C. rugosa, and C. tropicalis, which are known as the causal agents of candidiasis. We failed to reveal any correlation between the abundance of particular yeast species in the house dust, residential characteristics, and the atopic dermatitis of the inhabitants.

Air Microbiology↗
PubMed2005

[Screening of HBeAgTP interacting proteins in hepatocytes with yeast-two hybrid technique].

OBJECTIVE: To screen proteins in hepatocytes interacting with HBeAg transactivated protein (HBeAgTP) with yeast-two hybrid technique for investigating the biological functions of HBeAgTP. METHODS: Suppression subtractive hybridization (SSH) and bioinformatics techniques were used for screening and cloning of the target genes transactivated by HBeAg. The HBeAgTP gene was amplified by polymerase chain reaction (PCR) and HBeAgTP bait plasmid was constructed with yeast-two hybrid system 3, and then transformed into yeast AH109. The transformed yeast mated with yeast Y187 containing liver cDNA library plasmid in 2 x YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) and synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing X-gal for selecting two times and screening. After extracting and sequencing of plasmid from blue colonies, the results were analyzed by bioinformatics. RESULTS: HBeAgTP gene was successfully cloned and expressed in yeast cells. Fifteen genes in twenty-four positive colonies were obtained using yeast-two hybrid technique. CONCLUSION: HBeAgTP conjugated protein genes were successfully cloned, along with the genes involved in transcription and translation of proteins, immunoloregulation, materials and energy metabolism in vivo.

Hepatitis B e Antigens↗
PubMed2006

Screening of genes for proteins interacting with the PS1TP5 protein of hepatitis B virus: probing a human leukocyte cDNA library using the yeast two-hybrid system.

BACKGROUND: The hepatitis B virus (HBV) genome includes S, C, P and X regions. The S region is divided into four subregions of pre-pre-S, pre-S1, pre-S2 and S. PS1TP5 (human gene 5 transactivated by pre-S1 protein of HBV) is a novel target gene transactivated by the pre-S1 protein that has been screened with a suppression subtractive hybridization technique in our laboratory (GenBank accession: AY427953). In order to investigate the biological function of the PS1TP5 protein, we performed a yeast two-hybrid system 3 to screen proteins from a human leukocyte cDNA library interacting with the PS1TP5 protein. METHODS: The reverse transcription polymerase chain reaction (RT-PCR) was performed to amplify the gene of PS1TP5 from the mRNA of HepG2 cells and the gene was then cloned into the pGEM-T vector. After being sequenced and analyzed with Vector NTI 9.1 and NCBI BLAST software, the target gene of PS1TP5 was cut from the pGEM-T vector and cloned into a yeast expression plasmid pGBKT7, then "bait" plasmid pGBKT7-PS1TP5 was transformed into the yeast strain AH109. The yeast protein was isolated and analyzed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting hybridization. After expression of the pGBKT7-PS1TP5 fusion protein in the AH109 yeast strain was accomplished, a yeast two-hybrid screening was performed by mating AH109 with Y187 containing a leukocyte cDNA library plasmid. The mated yeast was plated on quadruple dropout medium and assayed for alpha-gal activity. The interaction between the PS1TP5 protein and the proteins obtained from positive colonies was further confirmed by repeating the yeast two-hybrid screen. After extracting and sequencing of plasmids from blue colonies we carried out a bioinformatic analysis. RESULTS: Forty true positive colonies were selected and sequenced, full length sequences were obtained and we searched for homologous DNA sequences from GenBank. Among the 40 positive colonies, 23 coding genes with known functions were obtained, including Homo sapien leukocyte adhesion protein p150, 95, interleukin 2 receptor gamma chain, PALM2-AKAP2 protein (PALM2-AKAP2), eukaryotic translation initiation factor 4A, beta-2-microglobin, solute carrier family 9 (sodium/hydrogen exchanger), calreticulin, asialoglycoprotein receptor 1 (ASGR1), MHC class II lymphocyte antigen, cytochrome c oxidase subunit 1, lymphocyte antigen 86 (LY86) and lymphocyte cytosolic protein 1. One novel gene with unknown function was found and named as PS1TP5BP1. After being electronically spliced, it was deposited in GenBank (accession number: DQ471327). CONCLUSIONS: Genes of proteins interacting with PS1TP5 were successfully screened from leukocyte cDNA library. These results suggested that PS1TP5 was closely correlated with immunoregulation, carbohydrate metabolism, signal transduction, the formation of hepatic fibrosis and initiation and development of tumors and also brought some new clues for further studying the biological functions of the pre-S1 protein.

Amino Acid Sequence↗
PubMed1986

Expression of cDNAs for acetylcholine receptor subunits in the yeast cell plasma membrane.

Yeast cells transformed with a plasmid containing cDNA encoding the alpha or delta subunit of the Torpedo californica acetylcholine receptor synthesize a protein. The expected molecular mass, antigenic specificity, and ligand-binding properties (in the case of the alpha subunit) of the subunits in yeast are similar to those of the subunits in T. californica membranes. The subunits are inserted into the yeast plasma membrane, demonstrating for the first time that yeast has the apparatus to express and insert foreign proteins into its plasma membrane. The alpha subunit constitutes approximately 1% of the yeast membrane proteins, and its density is about the same in the plasma membrane of yeast as in the receptor-rich electric organ of Electrophorus electricus. In view of the widely available technology for obtaining large quantities of yeast proteins, yeast cells may prove ideal for amplifying the amounts of interesting membrane-bound proteins available so that physical and biochemical studies can be made easily.

Animals↗
PubMed1981

[Response of chickens to the addition of yeasts of various origin to broiler feed mixtures].

The bioassays were aimed at testing the safety of complete starter and fattening broiler feed mixtures containing yeasts produced from sulphite liquors, synthetic ethanol and sulphite-ethanol substrate. The yeasts were included in the formulation of the mixtures at a 6% and 10% concentration and were enriched with methionine and B12. The following can be stated on the basis of the obtained results and evaluation of the over-all health state of the chickens: the effort to demonstrate a direct toxic effect of the tested yeasts on the chick organism by biochemical and haematological parameters failed,--at a 10% yeast concentration a tendency to a decreasing of chick live weight occurred towards the end of the experiment, irrespective of the origin of the yeasts,--the haemorrhages testifying to haemorrhagic diathesis, observed in different stages, might be caused by increased oxigenation of vitamin K, as suggested by our experience and by literary data: some role might also be played by stress from coccidiosis, which reduces the level of this vitamin,--the haemorrhages were more pronounced in the groups with a 10% concentration of yeasts,--although no direct toxic effect of yeasts was clearly demonstrated, it can be recommended on the basis of patho-anatomic findings that the yeasts should not constitute more than 6% of the volume of broiler mixtures and that the content of vitamin K should be increased to 400 mg per 100 kg.

Animal Feed↗
PubMed1997

A crossreactivity at the immunoglobulin E level of the cell wall mannoproteins of Candida albicans with other pathogenic Candida and airborne yeast species.

BACKGROUND: Candida albicans crossreacts with Saccharomyces cerevisiae or Pityrosporum ovale at the IgE level. However, the extent of crossreactivity of C. albicans with other yeast species is not known. OBJECTIVE: The crossreactivity at the immunoglobulin E (IgE) level of Candida albicans with other pathogenic Candida species and to the airborne yeast species Cryptococcus and Rhodotorula was studied by immunoblot analysis. METHODS: Crude antigens, designated as heat extract, were prepared from 13 different yeast species and a dot blot test was performed to detect IgE antibodies against each of the heat extracts in 349 patients with allergies who were positive for IgE antibodies against C. albicans in a CAP system. RESULTS: In the dot blot test, most of the sera reacted with the heat extracts of not only C. albicans but also those prepared from the other yeast species. The sera of 41 of the 349 patients (11.7%) reacted with the heat extracts of all 13 yeast species. The extent of the binding of IgE antibodies to multiple yeast species correlated with both the fluorescence intensities measured in the CAP system and the intensities of dots generated by the heat extract of C. albicans in the dot blot test. In an inhibition dot blot test, mannoproteins, but not proteins, of C. albicans strongly inhibited the subsequent binding of IgE antibodies to all yeast species. CONCLUSION: Our data suggest that the C. albicans mannoproteins are responsible for the crossreactivity among these yeast species at the IgE level.

Air Microbiology↗
PubMed1995

Oral yeast flora of a Kalahari population.

During an epidemiological survey of 181 individuals working or residing in the Kalahari National Gemsbok Park, swabs were taken from the dorsal surfaces of their tongues to determine a possible association between oral yeasts and clinically observed oral lesions as well as other underlying conditions detectable by serum chemistry. Identification of yeasts was performed with a commercially available identification system, namely the ATB 32C (Montalieu, Vercieu). Yeasts were isolated from 30.4 per cent (n = 55) of individuals, of whom 43.6 per cent (n = 24) had only Candida albicans, 3.6 per cent (n = 2) had C. albicans together with other yeasts and 52.7 per cent (n = 29) had other yeasts. Many of these yeasts were not the commonly encountered clinical isolates. The results revealed a significant association (p < 0.02) between yeasts (n = 55) and low serum iron concentrations (n = 50). A highly significant (p < 0.001) association was also found between smoking (n = 112) and the presence of clinically detectable oral lesions, notably leukoplakia (n = 21) and mucosal atrophy. The findings of this study reveal that a significant association exists between the oral yeast flora and serum iron and glucose, as well as between smoking and oral mucosal lesions.

Adolescent↗
PubMed1998

Functional comparison of the yeast scERV1 and scERV2 genes.

The yeast scERV1 gene is the first representative of a new emerging gene family. Its gene product is essential for the yeast cell and is involved in the biogenesis of mitochondria and the regulation of the cell cycle. Recently the general importance of the gene for the eukaryotic cell was shown by the identification of a structural and functional human homologue. The homologous mammalian ALR (augmenter of liver regeneration) genes from man, mouse and rat are important for different developmental stages of the organism as for example in spermatogenesis and the regeneration of damaged liver organs. Latest research identified an intron with an unusual 3' branch site in the 5' region of the yeast scERV1 gene. Analysis of the now available complete genome sequence from Saccharomyces cerevisiae identified a second yeast gene with homologies to scERV1 on chromosome 16. The corresponding gene product has a length of 196 amino acids similar to the 189 residues of the scERV1 protein and exhibits 30% identical amino acid residues in the highly conserved carboxy-terminal part of the polypeptides. Because of the structural similarities the new gene will be termed scERV2 from now on. For the scERV1 gene product it has just been shown that it is associated with yeast mitochondria. Analysis of the amino-terminal part of the putative scERV2 protein also identifies a typical leader sequence for import into mitochondria. The comparison of cDNA and genomic DNA from the scERV2 gene shows that no intron is present in this gene. To investigate the functional relation between the two yeast genes disruption experiments and complementation studies of mutants from scERV1 were performed. In addition the expression of messenger RNA under 15 different growth conditions was investigated by detailed Northern hybridization studies. Both genes show a complex and distinct expression pattern for their transcripts and are highly regulated under different physiological conditions. Moreover correct and efficient splicing of the transcript from the scERV1 gene was found to vary with the physiological state of the yeast cell, as further verified by reverse transcription-polymerase chain reaction analysis of transcripts from galactose-grown yeast cells.

Blotting, Northern↗
PubMed1998

Modeling brewers' yeast flocculation

Flocculation of yeast cells occurs during the fermentation of beer. Partway through the fermentation the cells become flocculent and start to form flocs. If the environmental conditions, such as medium composition and fluid velocities in the tank, are optimal, the flocs will grow in size large enough to settle. After settling of the main part of the yeast the green beer is left, containing only a small amount of yeast necessary for rest conversions during the next process step, the lagering. The physical process of flocculation is a dynamic equilibrium of floc formation and floc breakup resulting in a bimodal size distribution containing single cells and flocs. The floc size distribution and the single cell amount were measured under the different conditions that occur during full scale fermentation. Influences on flocculation such as floc strength, specific power input, and total number of yeast cells in suspension were studied. A flocculation model was developed, and the measured data used for validation. Yeast floc formation can be described with the collision theory assuming a constant collision efficiency. The breakup of flocs appears to occur mainly via two mechanisms, the splitting of flocs and the erosion of yeast cells from the floc surface. The splitting rate determines the average floc size and the erosion rate determines the number of single cells. Regarding the size of the flocs with respect to the scale of turbulence, only the viscous subrange needs to be considered. With the model, the floc size distribution and the number of single cells can be predicted at a certain point during the fermentation. For this, the bond strength between the cells, the fractal dimension of the yeast, the specific power input in the tank and the number of yeast cells that are in suspension in the tank have to be known. Copyright 1998 John Wiley & Sons, Inc.

Journal Article↗
PubMed2005

Quantitative analysis of wine yeast gene expression profiles under winemaking conditions.

Wine fermentation is a dynamic and complex process in which the yeast cell is subjected to multiple stress conditions. A successful adaptation involves changes in gene expression profiles where a large number of genes are up- or downregulated. Functional genomic approaches are commonly used to obtain global gene expression profiles, thereby providing a comprehensive view of yeast physiology. We used SAGE to quantify gene expression profiles in an industrial strain of Saccharomyces cerevisiae under winemaking conditions. The transcriptome of wine yeast was analysed at three stages during the fermentation process, mid-exponential phase, and early- and late-stationary phases. Upon correlation with the yeast genome, we found three classes of transcripts: (a) sequences that corresponded to ORFs; (b) expressed sequences from intergenic regions; and (c) messengers that did not match the published reference yeast genome. In all fermentation phases studied, the most highly expressed genes related to energy production and stress response. For many pathways, including glycolysis, different transcript levels were observed during each phase. Different isoenzymes, including hexose transporters (HXT), were differentially induced, depending on the growth phase. About 10% of transcripts matched non-annotated ORF regions within the yeast genome and could correspond to small novel genes originally omitted in the first gene annotation effort. Up to 22% of transcripts, particularly at late-stationary phase, did not match any known location within the genome. As the available reference yeast genome was obtained from a laboratory strain, these expressed sequences could represent genes only expressed by an industrial yeast strain. Further studies are necessary to identify the role of these potential genes during wine fermentation.

Cluster Analysis↗