Interactions between trans-resveratrol and CpLIP2 lipase/acyltransferase: Evidenced by fluorescence and in silico.

We have examined the trans-resveratrol/lipase interaction by quantitative and qualitative analyses of fluorescence spectra, molecular docking and quantum-chemical calculations at DFT level. Interactions of CpLIP2 from C. parapsilosis CBS 604 and trans-resveratrol were confirmed with a major contribution of tryptophan residues to fluorescence quenching. A thermodynamic study across a wide temperature range was consistent with the presence of a single binding site with a binding free energy of -24 kJ/mol. Nevertheless, trans-resveratrol competitively inhibited CpLIP2 activity. Molecular docking and quantum-chemical calculations were consistent with a strong binding of trans-resveratrol to the CpLIP2 catalytic site via electrostatic and hydrophobic forces. The structural analysis quantitatively revealed an energy transfer from W51 and W350 to trans-resveratrol with a distance of 32 Å. Precise understanding of trans-resveratrol/CpLIP2 interactions has important implications on lipases for screening of stilbenoid.

Population structure and comparative genome hybridization of European flor yeast reveal a unique group of Saccharomyces cerevisiae strains with few gene duplications in their genome.

Wine biological aging is a wine making process used to produce specific beverages in several countries in Europe, including Spain, Italy, France, and Hungary. This process involves the formation of a velum at the surface of the wine. Here, we present the first large scale comparison of all European flor strains involved in this process. We inferred the population structure of these European flor strains from their microsatellite genotype diversity and analyzed their ploidy. We show that almost all of these flor strains belong to the same cluster and are diploid, except for a few Spanish strains. Comparison of the array hybridization profile of six flor strains originating from these four countries, with that of three wine strains did not reveal any large segmental amplification. Nonetheless, some genes, including YKL221W/MCH2 and YKL222C, were amplified in the genome of four out of six flor strains. Finally, we correlated ICR1 ncRNA and FLO11 polymorphisms with flor yeast population structure, and associate the presence of wild type ICR1 and a long Flo11p with thin velum formation in a cluster of Jura strains. These results provide new insight into the diversity of flor yeast and show that combinations of different adaptive changes can lead to an increase of hydrophobicity and affect velum formation.

Validation of a predictive model for the growth of Botrytis cinerea and Penicillium expansum on grape berries.

The objective of this study was to develop and to validate a model for predicting the combined effect of temperature and a(w) on the radial growth rate, mu, of Botrytis cinerea and Penicillium expansum on grape berries. The proposed strategy was based on the gamma-concept developed previously [Zwietering, M.H., Wijtzes, T., de Wit, J.C., van't Riet, K. 1992. A decision support system for prediction of the microbial spoilage in foods. Journal of Food Protection. 12, 973-979]: mu=mu(opt).gamma(T).gamma(a(w)), where the gamma functions were cardinal models with inflection (CMI), mu(opt) the radial growth rate on grape berries. Firstly, the cardinal temperatures and a(w)'s were estimated independently from experiments carried out on Potato Dextrose Agar. Secondly, the gamma concept was validated i/ on a synthetic grape juice medium (SGJ) and ii/ on a grape juice agar (GJA). Accuracy and bias factors were closer to 1 with the latter analogue, thus suggesting that GJA should be preferred to SGJ. Thirdly, an experimental protocol taken into account the isotropic nature of fungal growth was developed for estimating mu(opt) on grape berries. This study demonstrated that CMI's can be validated on agri-food products over a wide range of temperature and a(w) using the described methodology.

French Jura flor yeasts: genotype and technological diversity.

Fifty-four Saccharomyces cerevisiae strains were isolated from Jura "Vin Jaune" velum and characterized by conventional physiological and molecular tests including ITS RFLP and sequence analysis, karyotyping and inter delta typing. ITS RFLP and sequence revealed a specific group of related strains different from the specific profile of Sherry flor yeast caused by a 24 bp deletion in the ITS1 region described by Esteve-Zarzoso et al. (Antonie Van Leeuwenhoek 85:151-158, 2004). Interdelta typing, the most discriminative method, revealed a high diversity of Jura flor yeast strains and gathered strains in clusters unequally shared between the northern and southern part of the Jura vineyard. The assessment of phenotypic diversity among the isolated strains was investigated for three wine metabolites (ethanal, acetic acid, and sotolon) from micro scale velum tests. Except at an early stage of ageing, the production of these metabolites was not correlated to the five genetic groups obtained by interdelta typing, but correlated to the cellar where strains had been isolated. The different strains isolated in a cellar produced mostly one type of velum (thin or thick, grey or white); but thin and grey velums, recognized as responsible for high quality wines, were obtained more frequently for one of the five groups of delta genotypes.

Release of nucleotides and nucleosides during yeast autolysis: kinetics and potential impact on flavor.

Nucleotides, particularly 5'-nucleotides, are important flavoring agents found in many foods and beverages. Their precise effect on the flavor of wines aged on lees has not been examined previously. In this study nucleotides and nucleosides released by yeast during autolysis in a model wine system and in Champagne wines were identified and quantified, and their impact on wine flavor was determined. Ribonucleotides only were detected in yeast autolysate and in Champagne wines. In wines ribonucleotides were quantified by tandem mass spectrometry coupled to HPLC. The maximum concentration of total nucleotides was very low with a maximum of approximately 3 mg/L in wine aged on yeasts for 9 years. In young wines the most important nucleotide was 5'-UMP, but after 2 years of aging its concentration decreased and the concentration of 5'-GMP slowly increased. The threshold values of the most representative nucleotides in Champagne wines were higher than the concentrations found in the same wines. However, it is known that there is synergism between the different nucleotides and also in the presence of glutamic acid. This phenomenon could explain the difference observed in descriptive profiles of wines spiked with nucleotides.

Lack of correlation between trehalose accumulation, cell viability and intracellular acidification as induced by various stresses in Saccharomyces cerevisiae.

A pma1-1 mutant of Saccharomyces cerevisiae with reduced H(+)-ATPase activity and the isogenic wild-type strain accumulated high levels of trehalose in response to a temperature upshift to 40 degrees C and after addition of 10% ethanol, but only modest levels in response to a rapid drop in external pH and after addition of decanoic acid. There was, however, no correlation between the absolute levels of trehalose in the stressed cells and their viability. All these treatments induced a significant decrease in intracellular pH, and surprisingly, this decrease was very similar in both strains, indicating that intracellular acidification could not be the triggering mechanism for trehalose accumulation in response to stress. A careful investigation of metabolic parameters was carried out to explain how trehalose accumulated under the four different stress conditions tested. No single and common mechanism for trehalose accumulation could be put forward and the transcriptional activation of TPS1 was not unequivocally related to trehalose accumulation. Another finding was that a pma1-1 mutant exhibited a two- to threefold greater capacity to accumulate trehalose than the isogenic wild-type. This enhanced disaccharide synthesis could be attributed to a twofold higher trehalose-6-phosphate synthase activity, together with a fourfold higher content of intracellular UDP-Glc. In addition, this mutant showed 1.5-fold higher levels of ATP compared to the wild-type. The various stress treatments studied showed that a drop in intracellular pH does not correlate with trehalose accumulation. It is suggested that plasma membrane alteration could be the physiological trigger inducing trehalose accumulation in yeast.

Alteration in membrane fluidity and lipid composition, and modulation of H(+)-ATPase activity in Saccharomyces cerevisiae caused by decanoic acid.

Decanoic acid, a lipophilic agent, inhibited in vitro the plasma membrane H(+)-ATPase of Saccharomyces cerevisiae grown in YPD medium. Conversely, when decanoic acid (35 microM) was present in the growth medium, the measured H(+)-ATPase activity was four times higher than that of control cells. Km, and pH and orthovanadate sensitivity were the same for the two growth conditions, which indicated that H(+)-ATPase activation was not due to conformational changes in the enzyme. The activation process was not entirely reversible which showed that plasma membrane H(+)-ATPase activation is due to several mechanisms. 1,6-diphenyl-1,3,5-hexatriene anisotropy performed on protoplasts from cells grown in YPD revealed that as decanoic acid concentration was increased, anisotropy significantly decreased, i.e. membrance fluidity increased. Cells grown in media containing decanoic acid exhibited greater membrane fluidity compared with control cells. Furthermore, these cells did not show any fluidifying effect when increased concentrations of decanoic acid were added. Chemical analysis of cell membrane lipid composition revealed a modification in the distribution of the phospholipid fatty acids and sterols in cells grown in the presence of 35 microM decanoic acid compared with control cells. Our results support the view that the plasma membrane H(+)-ATPase activation induced by decanoic acid is correlated with an alteration in membrane lipid constituents.