Overproduction of 2-phenylethanol by industrial yeasts to improve organoleptic properties of bakers' products.

2-Phenylethanol (PEA), an important alcohol derived from phenylalanine, is involved in aroma and flavour of bakers' products. Four spontaneous mutants of an industrial bakers' yeast, V1 strain, were isolated for their resistance to p-fluoro-DL-phenylalanine (PFP), a toxic analogue of L-phenylalanine. Mutants overproduced this amino acid and showed variations in their internal pool for several other amino acids.

Overexpression of stress-related genes enhances cell viability and velum formation in Sherry wine yeasts.

Flor formation and flor endurance have been related to ability by Saccharomyces cerevisiae flor yeasts to resist hostile conditions such as oxidative stress and the presence of acetaldehyde and ethanol. Ethanol and acetaldehyde toxicity give rise to formation of reactive oxygen species (ROS) and loss of cell viability. Superoxide dismutases Sod1p and Sod2p and other proteins such as Hsp12p are involved in oxidative stress tolerance.

Selection of an autochthonous Saccharomyces strain starter for alcoholic fermentation of Sherry base wines.

Several indigenous Saccharomyces strains from musts were isolated in the Jerez de la Frontera region, at the end of spontaneous fermentation, in order to select the most suitable autochthonous yeast starter, during the 2007 vintage. Five strains were chosen for their oenological abilities and fermentative kinetics to elaborate a Sherry base wine. The selected autochthonous strains were characterized by molecular methods: electrophoretic karyotype and random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) and by physiological parameters: fermentative power, ethanol production, sugar consumption, acidity and volatile compound production, sensory quality, killer phenotype, desiccation, and sulphur dioxide tolerance.

Transcriptional regulation of fermentative and respiratory metabolism in Saccharomyces cerevisiae industrial bakers' strains.

Bakers' yeast-producing companies grow cells under respiratory conditions, at a very high growth rate. Some desirable properties of bakers' yeast may be altered if fermentation rather than respiration occurs during biomass production. That is why differences in gene expression patterns that take place when industrial bakers' yeasts are grown under fermentative, rather than respiratory conditions, were examined.

Increased biomass production of industrial bakers' yeasts by overexpression of Hap4 gene.

HAP4 encodes a transcriptional activator of respiration-related genes and so, redirection from fermentation to respiration flux should give rise to an increase in biomass production in Saccharomyces cerevisiae transformants that overexpress HAP4. With this aim, three bakers' yeasts, that is, V1 used for lean doughs, its 2-deoxy-D-glucose resistant derivative DOG21, and V3 employed for sweet doughs, were transformed with integrative cassettes that carried HAP4 gene under the control of constitutive promoter pTEF2; in addition VTH, DTH and 3TH transformants were selected and characterized. Transformants showed increased expression of HAP4 and respiration-related genes such as QCR7 and QCR8 with regard to parental, and similar expression of SUC2 and MAL12; these genes are relevant in bakers' industry.

pH and Pac1 control development and antifungal activity in Trichoderma harzianum.

In Trichoderma harzianum CECT 2413 external pH regulates essential functions such as growth rate, sporulation, cell and colony morphology, pattern of secreted proteins, gene expression or mycoparasitism-related enzymatic activities. pH regulation is mediated by the transcriptional factor Pac1 (homologous to PacC regulator in other fungi), encoded by pac1 whose expression increases with pH. Two pac1 mutants have been obtained from CECT 2413: P2.

QID74 Cell wall protein of Trichoderma harzianum is involved in cell protection and adherence to hydrophobic surfaces.

Trichoderma is widely used as biocontrol agent against phytopathogenic fungi, and as biofertilizer because of its ability to establish mycorriza-like association with plants. The key factor to the ecological success of this genus is the combination of very active mycoparasitic mechanisms plus effective defense strategies induced in plants. This work, different from most of the studies carried out that address the attacking mechanisms, focuses on elucidating how Trichoderma is able to tolerate hostile conditions.

Biocontrol mechanisms of Trichoderma strains.

The genus Trichoderma comprises a great number of fungal strains that act as biological control agents, the antagonistic properties of which are based on the activation of multiple mechanisms. Trichoderma strains exert biocontrol against fungal phytopathogens either indirectly, by competing for nutrients and space, modifying the environmental conditions, or promoting plant growth and plant defensive mechanisms and antibiosis, or directly, by mechanisms such as mycoparasitism. These indirect and direct mechanisms may act coordinately and their importance in the biocontrol process depends on the Trichoderma strain, the antagonized fungus, the crop plant, and the environmental conditions, including nutrient availability, pH, temperature, and iron concentration.

Genetic analysis of apomictic wine yeasts.

The Saccharomyces cerevisiae wine yeast IFI256 was selected because of its high fermentative capacity and tolerance to ethanol. Sporulation of the IFI256 strain produced two-spore asci unable to conjugate, but able to sporulate again and the spores produced two-spore asci in all cases. That process was studied for at least five generations.

New Saccharomyces cerevisiae baker's yeast displaying enhanced resistance to freezing.

Three procedures were used to obtain new Saccharomyces cerevisiae baker's yeasts with increased storage stability at -20, 4, 22, and 30 degrees C. The first used mitochondria from highly ethanol-tolerant wine yeast, which were transferred to baker's strains. Viability of the heteroplasmons was improved shortly after freezing.

Acetaldehyde and ethanol are responsible for mitochondrial DNA (mtDNA) restriction fragment length polymorphism (RFLP) in flor yeasts.

Flor yeasts grow and survive in fino sherry wine where the frequency of respiratory-deficient (petite) mutants is very low. Mitochondria from flor yeasts are highly acetaldehyde- and ethanol-tolerant, and resistant to oxidative stress. However, restriction fragment length polymorphism (RFLP) of mtDNA from flor yeast populations is very high and reflects variability induced by the high concentrations of acetaldehyde and ethanol of sherry wine on mtDNA.