Biomedical subjects

Florian F Bauer

Publications and source records attributed to Florian F Bauer.

14 recordsLinked to original sources

PubMed2006

The effect of increased yeast alcohol acetyltransferase and esterase activity on the flavour profiles of wine and distillates.

The fruity odours of wine are largely derived from the synthesis of esters and higher alcohols during yeast fermentation. The ATF1- and ATF2-encoded alcohol acetyltransferases of S. cerevisiae are responsible for the synthesis of ethyl acetate and isoamyl acetate esters, while the EHT1-encoded ethanol hexanoyl transferase is responsible for synthesizing ethyl caproate. However, esters such as these might be degraded by the IAH1-encoded esterase. The objectives of this study were: (a) to overexpress the genes encoding ester-synthesizing and ester-degrading enzymes in wine yeast; (b) to prepare Colombard table wines and base wines for distillation using these modified strains; and (c) to analyse and compare the ester concentrations and aroma profiles of these wines and distillates. The overexpression of ATF1 significantly increased the concentrations of ethyl acetate, isoamyl acetate, 2-phenylethyl acetate and ethyl caproate, while the overexpression of ATF2 affected the concentrations of ethyl acetate and isoamyl acetate to a lesser degree. The overexpression of IAH1 resulted in a significant decrease in ethyl acetate, isoamyl acetate, hexyl acetate and 2-phenylethyl acetate. The overexpression of EHT1 resulted in a marked increase in ethyl caproate, ethyl caprylate and ethyl caprate. The flavour profile of the wines and distillates prepared using the modified strains were also significantly altered as indicated by formal sensory analysis. This study offers prospects for the development of wine yeast starter strains with optimized ester-producing capability that could assist winemakers in their effort to consistently produce wine and distillates such as brandy to definable flavour specifications and styles.

Acetyltransferases↗

PubMed2006

Regulation of respiratory growth by Ras: the glyoxylate cycle mutant, cit2Delta, is suppressed by RAS2.

In Saccharomyces cerevisiae the Ras/cAMP/PKA signalling pathway controls multiple metabolic pathways, and alterations in the intracellular concentrations of cAMP through modification of signalling pathway factors can be lethal or result in severe growth defects. In this work, the important role of Ras2p in metabolic regulation during growth on the non-fermentable carbon source glycerol is further investigated. The data show that the overexpression of RAS2 suppresses the growth defect of the glyoxylate cycle citrate synthase mutant, cit2Delta. The overexpression results in enhanced proliferation and biomass yield when cells are grown on glycerol as sole carbon source, and increases citrate synthase activity and intracellular citrate concentration. Interestingly, the suppression of cit2Delta and the enhanced proliferation and biomass yield are only observed when RAS2 is overexpressed and not in strains containing the constitutively active allele RAS2(val19). However, both RAS2 and RAS2(val19)upregulated citrate synthase activity. We propose that the RAS2 overexpression results in a combination of general upregulation of respiratory growth capacity and an increase in mitochondrial citrate/citrate synthases, which together, complement the metabolic requirements of the cit2Delta mutant. The data therefore provide new evidence for the role of Ras2p as a powerful modulator of metabolism during growth on a non-fermentable carbon source.

Base Sequence↗

PubMed2006

Rapid screening of the fermentation profiles of wine yeasts by Fourier transform infrared spectroscopy.

A rapid screening method for the evaluation of the major fermentation products of Saccharomyces wine yeasts was developed using Fourier transform infrared spectroscopy and principal component factor analysis. Calibration equations for the quantification of volatile acidity, glycerol, ethanol, reducing sugar and glucose concentrations in fermented Chenin blanc and synthetic musts were derived from the Fourier transform infrared spectra of small-scale fermentations. The accuracy of quantification of volatile acidity in both Chenin blanc and synthetic must was excellent, and the standard error of prediction was 0.07 g l(-1) and 0.08 g l(-1), respectively. The respective standard error of prediction in Chenin blanc and synthetic musts for ethanol was 0.32% v/v and 0.31% v/v, for glycerol was 0.38 g l(-1) and 0.32 g l(-1), for reducing sugar in Chenin blanc must was 0.56 g l(-1) and for glucose in synthetic must was 0.39 g l(-1). These values were in agreement with the accuracy obtained by the respective reference methods used for the quantification of the components. The screening method was applied to quantify the fermentation products of glycerol-overproducing hybrid yeasts and commercial wine yeasts. Principal component factor analysis of the fermentation data facilitated an overall comparison of the fermentation profiles (in terms of the components tested) of the strains. The potential of Fourier transform infrared spectroscopy as a tool to rapidly screen the fermentative properties of wine yeasts and to speed up the evaluation processes in the initial stages of yeast strain development programs is shown.

Ethanol↗

PubMed2006

The regulation of Saccharomyces cerevisiae FLO gene expression and Ca2+ -dependent flocculation by Flo8p and Mss11p.

The ability of many microorganisms to modify adhesion-related properties of their cell surface is of importance for many processes, including substrate adhesion, cell-cell adhesion, invasive growth, pathogenic behaviour and biofilm formation. In the yeast Saccharomyces cerevisiae, a group of structurally related, cell-wall associated proteins encoded by the FLO gene family are directly responsible for many of the cellular adhesion phenotypes displayed by this organism. Previous research has suggested that the differential transcription of FLO genes determines specific adhesion phenotypes. However, the transcriptional regulation of most FLO genes remains poorly understood. Here we show that the transcriptional activator Mss11p, which has previously been shown to be involved in the regulation of starch degradation, the formation of pseudohyphae and haploid invasive growth, also acts as a strong inducer of flocculation. The data indicate that Mss11p induces flocculation together with Flo8p, and that FLO1 is the dominant target gene of the two factors in this process. The deletion of MSS11 leads to a non-flocculent phenotype, and specific domains of Mss11p that are critical for the induction of flocculation are identified. The data clearly show that several essential transcription factors are shared by at least two flocculation genes that control different adhesion phenotypes.

Calcium↗

PubMed2006

The effect of increased branched-chain amino acid transaminase activity in yeast on the production of higher alcohols and on the flavour profiles of wine and distillates.

In Saccharomyces cerevisiae, branched-chain amino acid transaminases (BCAATases) are encoded by the BAT1 and BAT2 genes. BCAATases catalyse the transfer of amino groups between those amino acids and alpha-keto-acids. alpha-Keto-acids are precursors for the biosynthesis of higher alcohols, which significantly influence the aroma and flavour of yeast-derived fermentation products. The objective of this study was to investigate the influence of BAT-gene expression on general yeast physiology, on aroma and flavour compound formation and on the sensory characteristics of wines and distillates. For this purpose, the genes were overexpressed and deleted in a laboratory strain, BY4742, and overexpressed in an industrial wine yeast strain, VIN13. The data show that, with the exception of a slow growth phenotype observed for the BAT1 deletion strain, the fermentation behaviour of the strains was unaffected by the modifications. The chemical and sensory analysis of fermentation products revealed a strong correction between BAT gene expression and the formation of many aroma compounds. The data suggest that the adjustment of BAT gene expression could play an important role in assisting winemakers in their endeavour to produce wines with specific flavour profiles.

Alcohols↗

PubMed2005

Characteristics of Flo11-dependent flocculation in Saccharomyces cerevisiae.

The FLO11-encoded flocculin is required for a variety of important phenotypes in Saccharomyces cerevisiae, including flocculation, adhesion to agar and plastic, invasive growth, pseudohyphae formation and biofilm development. We present evidence that Flo11p belongs to the Flo1-type class of flocculins rather than to the NewFlo class. Both Flo1-type and NewFlo yeast flocculation are inhibited by mannose. NewFlo flocculation, however, is also inhibited by several other carbohydrates including glucose, maltose and sucrose. These differences have in at least one case been shown to reflect differences in the structure of the carbohydrate-binding site of the flocculins. We report that Flo11p-dependent flocculation is inhibited by mannose, but not by glucose, maltose or sucrose. Furthermore, Flo11p contains a peptide sequence highly similar to one that has been shown to characterise Flo1-type flocculins. Further characterisation of the properties of Flo11p-dependent flocculation revealed that it is dependent on calcium, occurs only at cell densities greater than 1 x 10(8) ml(-1), and only occurs at acidic pH.

Amino Acid Sequence↗

PubMed2004

Mss11p is a central element of the regulatory network that controls FLO11 expression and invasive growth in Saccharomyces cerevisiae.

The invasive and filamentous growth forms of Saccharomyces cerevisiae are adaptations to specific environmental conditions, under particular conditions of limited nutrient availability. Both growth forms are dependent on the expression of the FLO11 gene, which encodes a cell-wall-associated glycoprotein involved in cellular adhesion. A complex regulatory network consisting of signaling pathways and transcription factors has been associated with the regulation of FLO11. Mss11p has been identified as a transcriptional activator of this gene, and here we present an extensive genetic analysis to identify functional relationships between Mss11p and other FLO11 regulators. The data show that Mss11p is absolutely required for the activation of FLO11 by most proteins that have previously been shown to affect FLO11 expression, including the signaling proteins Ras2p, Kss1p, and Tpk2p, the activators Tec1p, Flo8p, and Phd1p, and the repressors Nrg1p, Nrg2p, Sok2p, and Sfl1p. The genetic evidence furthermore suggests that Mss11p activity is not dependent on the presence of any of the above-mentioned factors and that the protein also regulates other genes involved in cellular adhesion phenotypes. Taken together, the data strongly suggest a central role for Mss11p in the regulatory network controlling FLO11 expression, invasive growth, and pseudohyphal differentiation.

Cell Differentiation↗

PubMed2004

Principal component analysis applied to Fourier transform infrared spectroscopy for the design of calibration sets for glycerol prediction models in wine and for the detection and classification of outlier samples.

Principal component analysis (PCA) was used to identify the main sources of variation in the Fourier transform infrared (FT-IR) spectra of 329 wines of various styles. The FT-IR spectra were gathered using a specialized WineScan instrument. The main sources of variation included the reducing sugar and alcohol content of the samples, as well as the stage of fermentation and the maturation period of the wines. The implications of the variation between the different wine styles for the design of calibration models with accurate predictive abilities were investigated using glycerol calibration in wine as a model system. PCA enabled the identification and interpretation of samples that were poorly predicted by the calibration models, as well as the detection of individual samples in the sample set that had atypical spectra (i.e., outlier samples). The Soft Independent Modeling of Class Analogy (SIMCA) approach was used to establish a model for the classification of the outlier samples. A glycerol calibration for wine was developed (reducing sugar content < 30 g/L, alcohol > 8% v/v) with satisfactory predictive ability (SEP = 0.40 g/L). The RPD value (ratio of the standard deviation of the data to the standard error of prediction) was 5.6, indicating that the calibration is suitable for quantification purposes. A calibration for glycerol in special late harvest and noble late harvest wines (RS 31-147 g/L, alcohol > 11.6% v/v) with a prediction error SECV = 0.65 g/L, was also established. This study yielded an analytical strategy that combined the careful design of calibration sets with measures that facilitated the early detection and interpretation of poorly predicted samples and outlier samples in a sample set. The strategy provided a powerful means of quality control, which is necessary for the generation of accurate prediction data and therefore for the successful implementation of FT-IR in the routine analytical laboratory.

Calibration↗

PubMed2003

Mss11p is a transcription factor regulating pseudohyphal differentiation, invasive growth and starch metabolism in Saccharomyces cerevisiae in response to nutrient availability.

In Saccharomyces cerevisiae, the cell surface protein, Muc1p, was shown to be critical for invasive growth and pseudohyphal differentiation. The transcription of MUC1 and of the co-regulated STA2 glucoamylase gene is controlled by the interplay of a multitude of regulators, including Ste12p, Tec1p, Flo8p, Msn1p and Mss11p. Genetic analysis suggests that Mss11p plays an essential role in this regulatory process and that it functions at the convergence of at least two signalling cascades, the filamentous growth MAPK cascade and the cAMP-PKA pathway. Despite this central role in the control of filamentous growth and starch metabolism, the exact molecular function of Mss11p is unknown. We subjected Mss11p to a detailed molecular analysis and report here on its role in transcriptional regulation, as well as on the identification of specific domains required to confer transcriptional activation in response to nutritional signals. We show that Mss11p contains two independent transactivation domains, one of which is a highly conserved sequence that is found in several proteins with unidentified function in mammalian and invertebrate organisms. We also identify conserved amino acids that are required for the activation function.

Blotting, Northern↗

PubMed2003

Cellular differentiation in response to nutrient availability: The repressor of meiosis, Rme1p, positively regulates invasive growth in Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, the transition from a nutrient-rich to a nutrient-limited growth medium typically leads to the implementation of a cellular adaptation program that results in invasive growth and/or the formation of pseudohyphae. Complete depletion of essential nutrients, on the other hand, leads either to entry into a nonbudding, metabolically quiescent state referred to as G0 in haploid strains or to meiosis and sporulation in diploids. Entry into meiosis is repressed by the transcriptional regulator Rme1p, a zinc-finger-containing DNA-binding protein. In this article, we show that Rme1p positively regulates invasive growth and starch metabolism in both haploid and diploid strains by directly modifying the transcription of the FLO11 (also known as MUC1) and STA2 genes, which encode a cell wall-associated protein essential for invasive growth and a starch-degrading glucoamylase, respectively. Genetic evidence suggests that Rme1p functions independently of identified signaling modules that regulate invasive growth and of other transcription factors that regulate FLO11 and that the activation of FLO11 is dependent on the presence of a promoter sequence that shows significant homology to identified Rme1p response elements (RREs). The data suggest that Rme1p functions as a central switch between different cellular differentiation pathways.

Base Sequence↗

PubMed2002

Selectivity in overlapping MAP kinase cascades.

Some protein kinases operate in more than one mitogen-activated protein-kinase (MAPK) cascade. We here address the question whether specificity of the cascades necessitates physical sequestration of these "promiscuous" kinases (e.g. by binding to scaffolds). A model is constructed, in which two MAPK cascades depend on a single MAP-kinase kinase that is not sequestered in two subpopulations. We show that in this model selective signal transduction is possible provided that there is an additional interaction at the MAP-kinase level, there is no simultaneous activation of more than one response by either signal. We discuss a number of additional interactions that can generate the selectivity, as well as some kinetic features by which this mechanism may be recognized experimentally.

Adaptation, Physiological↗

PubMed2002

Carnitine biosynthesis in Neurospora crassa: identification of a cDNA coding for epsilon-N-trimethyllysine hydroxylase and its functional expression in Saccharomyces cerevisiae.

The biosynthesis of L-carnitine in eukaryotic organisms was first elucidated in the ascomycete Neurospora crassa. The first step of the pathway is catalysed by epsilon-N-trimethyllysine hydroxylase (TMLH), which converts epsilon-N-trimethyllysine into beta-hydroxy-N-epsilon-trimethyllysine in a reaction dependent on alpha-ketoglutarate, Fe2+ and oxygen. Here we report on the cloning of the N. crassa TMLH cDNA and its functional expression in Saccharomyces cerevisiae. The TMLH cDNA contains an open reading frame of 1413 base pairs encoding a predicted polypeptide of 471 amino acids. The Michaelis-Menten constants of the heterologously expressed enzyme were determined for epsilon-N-trimethyllysine, alpha-ketoglutarate, Fe2+ and correspond to 0.33 mM, 133 microM and 46 microM, respectively.

Amino Acid Sequence↗

PubMed2002

Meeting the consumer challenge through genetically customized wine-yeast strains.

Wine producers are facing intensifying competition brought about by a widening gap between wine production and wine consumption, a shift of consumer preferences away from basic commodity wine to top quality wine, and economic globalization. Consequently, they are calling for a total revolution in the 'magical' world of wine. The process of transforming the wine industry from a production- to a market-orientated industry results in an increasing dependence on, amongst others, biotechnological innovation. Market-orientated wine-yeast strains are currently being developed for the cost-competitive production of wine with minimized resource inputs, improved quality and low environmental impact. The emphasis is on the development of Saccharomyces cerevisiae strains with improved fermentation, processing and biopreservation abilities, and capacities for an increase in the wholesomeness and sensory quality of wine.

Consumer Behavior↗

PubMed2002

The sensing of nutritional status and the relationship to filamentous growth in Saccharomyces cerevisiae.

Heterotrophic organisms rely on the ingestion of organic molecules or nutrients from the environment to sustain energy and biomass production. Non-motile, unicellular organisms have a limited ability to store nutrients or to take evasive action, and are therefore most directly dependent on the availability of nutrients in their immediate surrounding. Such organisms have evolved numerous developmental options in order to adapt to and to survive the permanently changing nutritional status of the environment. The phenotypical, physiological and molecular nature of nutrient-induced cellular adaptations has been most extensively studied in the yeast Saccharomyces cerevisiae. These studies have revealed a network of sensing mechanisms and of signalling pathways that generate and transmit the information on the nutritional status of the environment to the cellular machinery that implements specific developmental programmes. This review integrates our current knowledge on nutrient sensing and signalling in S. cerevisiae, and suggests how an integrated signalling network may lead to the establishment of a specific developmental programme, namely pseudohyphal differentiation and invasive growth.

Adaptation, Physiological↗