Genome structure reveals the diversity of mating mechanisms in Saccharomyces cerevisiae x Saccharomyces kudriavzevii hybrids, and the genomic instability that promotes phenotypic diversity.

Interspecific hybridization has played an important role in the evolution of eukaryotic organisms by favouring genetic interchange between divergent lineages to generate new phenotypic diversity involved in the adaptation to new environments. This way, hybridization between Saccharomyces species, involving the fusion between their metabolic capabilities, is a recurrent adaptive strategy in industrial environments. In the present study, whole-genome sequences of natural hybrids between Saccharomyces cerevisiae and Saccharomyces kudriavzevii were obtained to unveil the mechanisms involved in the origin and evolution of hybrids, as well as the ecological and geographic contexts in which spontaneous hybridization and hybrid persistence take place. Although Saccharomyces species can mate using different mechanisms, we concluded that rare-mating is the most commonly used, but other mechanisms were also observed in specific hybrids. The preponderance of rare-mating was confirmed by performing artificial hybridization experiments. The mechanism used to mate determines the genomic structure of the hybrid and its final evolutionary outcome. The evolution and adaptability of the hybrids are triggered by genomic instability, resulting in a wide diversity of genomic rearrangements. Some of these rearrangements could be adaptive under the stressful conditions of the industrial environment.

Aroma production and fermentation performance of S. cerevisiae × S. kudriavzevii natural hybrids under cold oenological conditions.

This work aims to describe the wine fermentation characteristics of 23 natural S. cerevisiae × S. kudriavzevii hybrid yeasts related to fermentative environments isolated from different regions and their significance for the aroma spectra of the produced wines. Fermentations were performed at 12 °C in artificial must, and S. cerevisiae and S. kudriavzevii pure species strains were used for comparison purposes. We determined the relevant kinetic parameters of fermentation, the concentration of the main metabolites and the main aroma-related compounds produced after fermentation. The results revealed that some strains that show well-rounded characteristics could be profitable yeast starters for low-temperature fermentation in winemaking, such as wine hybrid SPG172 but, surprisingly, also beer hybrid CECT11002, adding the efficient fermentative kinetics to the high production of aroma-related compounds. In addition, a novel metabolic correlation between fermentation performance and aroma production is described.

A comparison of the performance of natural hybrids Saccharomyces cerevisiae × Saccharomyces kudriavzevii at low temperatures reveals the crucial role of their S. kudriavzevii genomic contribution.

Fermentation performance at low temperature is a common approach to obtain wines with better aroma, and is critical in industrial applications. Natural hybrids S. cerevisiae × S. kudriavzevii, isolated from fermentations in cold-climate European countries, have provided an understanding of the mechanisms of adaptation to grow at low temperature. In this work, we studied the performance of 23 S. cerevisiae × S. kudriavzevii hybrids at low temperature (8, 12 and 24 °C) to characterize their phenotypes. Kinetic parameters and spot tests revealed a different ability to grow at low temperature. Interestingly, the genome content of the S. kudriavzevii in hybrids was moderately correlated with a shorter lag phase, and the genetic origin of hybrids influenced their performance at low temperature (8 °C). The parental expression of cold marker genes (NSR1, GUT2 and GPD1) showed that the relative expression of the S. kudriavzevii alleles was higher than the expression of the S. cerevisiae alleles in hybrids with a better growth at low-temperatures. These results suggest that the genomic contribution of S. kudriavzevii to hybrids is important for improving the fitness of these strains at low temperature.

Effect of solid substrate fermentation on the nutritional quality of agro-industrial residues

El objetivo de este trabajo fue evaluar la composición química y la producción de gas in vitro de cinco residuos agro-industriales, antes y después de aplicar un proceso de fermentaci¢n en medio sólido. Paja de avena, paja de haba, rastrojo de maíz, bagaso de manzana y bagaso de agave fueron tratados usando dos hongos filamentosos, Trichoderma harzianum y Phanaerochaete chrysosporium. Los análisis químicos realizados fueron: determinación de proteína cruda, fibra detergente neutro, fibra detergente ácido, lignina, celulosa y hemicelulosa. Para la determinación de la producción de gas in vitro se utilizaron jeringuas de cristal calibradas, mientras que el perfil de ácidos grasos volátiles (AGV's) fue obtenido por cromatografía de gases. Los datos de producción de gas in vitro fueron ajustados usando las ecuaciones p=a+b(1-e-ct) propuesta por Orskov y McDonald y G=A/(1+[B/t]) propuesta por France et al (2000). Se observaron aumentos en el contenido de proteína cruda (P<0,05) al tratar paja de avena (20 por ciento), paja de haba (83 por ciento) y rastrojo de maíz (16 por ciento) con P. chrysosporium. El contenido de fibra detergente neutro fue reducido un 9,5 por ciento en paja de avena por los tratamientos (P<0,05). Con respecto a los parámetros de la producción del gas, los valores de b y c en bagaso de agave fueron mayores (57,4 por ciento y 7,5 por ciento, respectivamente) en el substrato tratado con P. chrysosporium en relación con otros tratamientos. De manera similar, valores más altos para el parámetro de A fueron observados en rastrojo de maíz (+22 por ciento) y bagaso de agave (+13 por ciento) tratados con P. chrysosporium. A pesar de estas diferencias aisladas, el análisis realizado demostró que la composición química, principalmente carbohidratos estructurales, no fue modificada bajo las condiciones de este estudio.