Physiological and molecular characterization of flor yeasts: Polymorphism of flor yeast populations

Abstract

Yeast strains which form velum on the surface of Sherry wine during the aging process have been isolated and characterized. According to their metabolic and molecular features most of the yeasts that were isolated belong to different races of Saccharomyces cerevisiae (beticus, cheresiensis, montuliensis and rouxii). Due to the conditions under which these yeasts were isolated, all strains have in common the capacity to develop a film as an adaptive mechanism which allows them to grow and survive in 15.5% vol. ethanol. All strains were prototrophs for amino acids and most vitamins but they gave different responses to the killer factor. However, whereas their physiological features were similar, they showed a great heterogeneity with regards to the nuclear and mitochondrial genome (mtDNA): DNA content per cell was quite variable (1.3 to 2n), electrophoretic karyotypes of nuclear genomes indicated a main pattern with some variations, and polymorphism shown by the mtDNA was very high. Under extreme conditions such as Sherry wine with 15.5% vol. ethanol, no fermentable sugar and an exclusively oxidative metabolism, cells hardly grow and the maintenance of a live population depends on survival and respiration, which in turn depend on the mtDNA. At the same time these environmental conditions are mutagenic for the mtDNA, causing an increase in variation. Thus, the polymorphism observed might reflect the enormous variability induced by the ethanol followed by the selection of those mtDNA sequences which make the mitochondria metabolically active under these conditions.

Yeast Population Dynamics during the Fermentation and Biological Aging of Sherry Wines

“…The Saccharomyces strains responsible for sherry wine aging constitute a special group of wine yeasts, which have been poorly studied at a molecular level. In this sense, only one attempt at the molecular characterization of these yeast strains using mtDNA restriction analysis and electrophoretic karyotyping has been made (11,15). In the present study, we have shown, for the first time, the evolution of yeast populations from alcoholic fermentation to biological aging in the production of fino sherry wines.…”

“…Mitochondrial DNA (mtDNA) restriction analysis and karyotyping were used to differentiate strains of S. cerevisiae. Restriction analysis of mtDNA was performed according to the work of Querol et al (19); HinfI was used as the most suitable restriction endonuclease for differentiation among S. cerevisiae flor and nonflor strains (11,15,19). DNA for electrophoretic karyotyping was prepared in agarose plugs as described by Carle and Olson (2).…”

“…Growth of yeasts on velum surfaces produces important changes in the characteristics of the wine due to the oxidative metabolism of the flor yeasts (17,18). Various microbiological studies on the fermentation (7,13,21,22,23) and aging (11,15,16) processes in the elaboration of sherry wines have been carried out. However, although some of these studies analyze the dynamics of yeast strains during the specific steps of sherry wine making (18), no complete monitoring of the whole process, from grape must to aged wine has been performed to date.…”

Mitotic Recombination and Genetic Changes inSaccharomyces cerevisiaeduring Wine Fermentation

“…The electrophoretic karyotypes of wine yeast strains differ in the number, size, and intensity of bands, allowing the identification of every strain by its chromosome pattern (37,40). Wine strains do not have a stable and defined karyotype, like flor yeasts (21), but their variability is not as high as that reported for baker's yeasts (5,10).…”

A Microtiter Plate Assay as a Reliable Method to Assure the Identification and Classification of the Veil-Forming Yeasts during Sherry Wines Ageing

“…The early methods related to taxonomy involved morphological studies and biochemical analyses of differences on fermentation and assimilation tests, where the substrates used were mainly dextrose, lactose, maltose, melibiose, raffinose, galactose and sucrose. These physiological properties were traditionally tested using Durham tubes in a liquid medium, which filled up with gas if fermentation occurred [4]. Nevertheless, both morphological and physiological characteristics may be influenced by culture conditions and spoilages and can provide ambiguous results.…”