DNA adduct formation in Saccharomyces cerevisiae following exposure to environmental pollutants, as in vivo model for molecular toxicity studies.

DNA adduction in the model yeast Saccharomyces cerevisiae was investigated after exposure to the fungicide penconazole and the reference genotoxic compound benzo(a)pyrene, for validating yeasts as a tool for molecular toxicity studies, particularly of environmental pollution. The effect of the toxicants on the yeast's growth kinetics was determined as an indicator of cytotoxicity. Fermentative cultures of S. cerevisiae were exposed to 2 ppm of Penconazole during different phases of growth; while 0.2 and 2 ppm of benzo(a)pyrene were applied to the culture medium before inoculation and on exponential cultures. Exponential respiratory cultures were also exposed to 0.2 ppm of B(a)P for comparison of both metabolisms. Penconazole induced DNA adducts formation in the exponential phase test; DNA adducts showed a peak of 54.93 adducts/109 nucleotides. Benzo(a)pyrene induced the formation of DNA adducts in all the tests carried out; the highest amount of 46.7 adducts/109 nucleotides was obtained in the fermentative cultures after the exponential phase exposure to 0.2 ppm; whereas in the respiratory cultures, 14.6 adducts/109 nucleotides were detected. No cytotoxicity was obtained in any experiment. Our study showed that yeast could be used to analyse DNA adducts as biomarkers of exposure to environmental toxicants.

Effect of temperature on Brettanomyces bruxellensis: metabolic and kinetic aspects.

The effect of temperatures ranging from 15 to 35 degrees C on a culture of Brettanomyces bruxellensis was investigated in regards to thermodynamics, metabolism, and kinetics. In this temperature range, we observed an increase in growth and production rates. The growth behavior was well represented using the Arrhenius model, and an apparent activation energy of 16.61 kcal/mol was estimated. A stuck fermentation was observed at 35 degrees C as represented by high cell death. The carbon balance established that temperature had no effect on repartition of the glucose consumption between biomass and products. Hence, the same biomass concentration was obtained for all temperatures, except at 35 degrees C. Moreover, using logistic and Luedeking-Piret models, we demonstrated that production rates of ethanol and acetic acid were partially growth associated. Parameters associated with growth (alpha eth and alpha aa) remained constant with changing temperature, whereas, parameters associated with the population (beta eth and beta aa) varied. Optimal values were obtained at 32 degrees C for ethanol and at 25 degrees C for acetic acid.

Effect of ammonium concentration on alcoholic fermentation kinetics by wine yeasts for high sugar content.

Kinetics of alcoholic fermentation by Saccharomyces cerevisiae wine strains in a synthetic medium with high sugar content were established for different nitrogen initial content and are presented for four strains. The composition of the medium was close to grape must except that the nitrogen source consisted mainly in ammonium and was varied from 120 to 290 mg N/l assimilable nitrogen. The overall nitrogen consumed was also estimated in order to determine nitrogen requirement variability. The effect of assimilable nitrogen was in general greater on sugar consumption rates than on growth and three kinds of effect on sugar consumption rates were observed: (i) existence of an optimal initial nitrogen level for a maximal sugar consumption rate (inhibition if excess), (ii) no effect of nitrogen beyond the intermediary level (saturation), (iii) sugar consumption rate proportional to the initial nitrogen level (activation). In all cases, the amount of consumed nitrogen increased with its initial concentration and so did the fructophilic capacity of the strains. The optimal requirement varied from 0.62 to 0.91 mg N/g of sugars according to different strains. There was no general correlation between the sugar assimilation rates and the nitrogen requirement.

Effects of penconazole on two yeast strains: growth kinetics and molecular studies.

The aim of this study consisted to evaluate the impact of a pesticide (penconazole) on the growth kinetics and genotoxicity on two yeast strains (Saccharomyces cerevisiae and Metschnikowia pulcherrima). When the penconazole was added at different phases of the growth of M. pulcherrima, no effect was noticed on the kinetics of yeast growth but DNA adducts were observed when penconazole was added in the exponential phase. Increasing doses (1-15 maximum residue limit) of the pesticide added at the beginning of the fermentation did not induce DNA adducts while kinetics were affected.

Influence of temperature and pH on Saccharomyces bayanus var. uvarum growth; impact of a wine yeast interspecific hybridization on these parameters.

The species Saccharomyces bayanus var. uvarum possesses interesting enological characteristics but produces high concentration of volatile fermentative compounds not desirable in Sauvignon blanc wines. Interspecific hybrids between Saccharomyces cerevisiae and S. bayanus var. uvarum were made in order to join the main parental advantages. Two hybrids were selected on the basis of their fermentation characteristics and their karyotypes, i.e. they have a different mitochondrial DNA. In order to produce these hybrids as active dry yeast to be used as starter in wine-making, their optimal environmental conditions for growth, i.e. temperature and pH, were determined as the objective of our work. Using a two-level factorial design it was found that the two parental strains have different optimal temperature but for the two strains, pH does not have a significant influence on growth. The influence of temperature on biomass productivity for hybrid strains were strictly identical, so we suppose that the main genes coding for temperature sensitivity were not contained in mitochondrial DNA, but in nuclear DNA. Moreover the reactions of hybrid strains to the temperature variations were similar to the one of S. bayanus var. uvarum. This latter strain could have a majority of genes responsible of temperature sensitivity dominant in comparison with those of the strain S. cerevisiae.

Tecnologías alternativas para a fermentaçäo alcoólica em Saccharomyces cerevisiae / Alternative tecnology for alcoholic fermentation by Saccharomyces cerevisiae

Apresenta-se uma revisäo sobre os parâmetros e técnicas da fermentaçäo alcoólica em Saccharomyces cerevisiae. Säo abordados processos de fermentaçäo em regime descontínuo (convencional e alimentado) e contínuo (fermentaçäo extrativa, com reciclagem celular, com floculaçäo de leveduras, com imobilizaçäo celular, acoplada a filtros de membranas e de fibras parosas). O processo descontínuo convencional pode levar a altos rendimentos, mas a produtividade é muito baixa, dificilmente ultrapassando 0,5 g etanol/l.h. O teor máximo no meio situa-se em geral na baixa de 80-90 g/l. Pelo processo descontínuo alimentado atenua-se a inibiçäo pelo substrato, o que permite elevar o teor de etanol no masto fermentado, além de melhorar a produtividade. As técnicas contínuas, embora ainda via de regra onerosas para a produçäo industrial de etanol em larga escala, têm tido avanças tecnológicas relevantes. Além de outras vantagens, o principal trunfo é o aumento acentuado da produtividade, que pode chegar a 80 g etanol/l.h., ou mais