Yeast Community Structures and Dynamics in Healthy andBotrytis-Affected Grape Must Fermentations

Abstract

Indigenous yeast population dynamics during the fermentation of healthy and Botrytis-affected grape juice samples from two regions in Greece, Attica and Arcadia, were surveyed. Species diversity was evaluated by using restriction fragment length polymorphism and sequence analyses of the 5.8S internal transcribed spacer and the D1/D2 ribosomal DNA (rDNA) regions of cultivable yeasts. Community-level profiles were also obtained by direct analysis of fermenting samples through denaturing gradient gel electrophoresis of 26S rDNA amplicons. Both approaches revealed structural divergences in yeast communities between samples of different sanitary states or geographical origins. In all cases, Botrytis infection severely perturbed the bioprocess of fermentation by dramatically altering species heterogeneity and succession during the time course. At the beginning and middle of fermentations, Botrytis-affected samples possessed higher levels of biodiversity than their healthy counterparts, being enriched with fermentative and/or spoilage species, such as Zygosaccharomyces bailii and Issatchenkia spp. or Kluyveromyces dobzhanskii and Kazachstania sp. populations that have not been reported before for wine fermentations. Importantly, Botrytis-affected samples exposed discrete final species dominance. Selection was not species specific, and two different populations, i.e., Saccharomyces cerevisiae in samples from Arcadia and Z. bailii in samples from Attica, could be recovered at the end of Botrytis-affected fermentations. The governing of wine fermentations by Z. bailii is reported for the first time and could elucidate the origins and role of this particular spoilage microbe for the wine industry. This is the first survey to compare healthy and Botrytis-affected spontaneous fermentations by using both culture-based and -independent molecular methods in an attempt to further illuminate the complex yeast ecology of grape must fermentations.Grape must fermentations are governed by dynamic yeast species assemblages, whose physiognomy is influenced by several chemical constraints and biological attributes. Among these factors, the chemical composition of the must, particular enological practices, and primary species richness/heterogeneity in the grape juice have been shown to determine yeast succession during the fermentation course and the final species dominance (12, 13). Accumulating data reveal additional factors that may designate the boundaries of yeast inhabitants, such as the grape variety and the geographical location of the vineyard (6,12,31,33,38). Biological invasions also influence resident yeast biota and may stimulate forces that shape community diversity, yet their impact on must fermentation has been underestimated in earlier literature (12,20). Botrytis is an important grape pathogen that dramatically changes the physicochemical state of berries and consequently may alter the structure of the yeast community (12,27). It has also been postulated that Botrytis infection may affect species succession during alcoh...

Botrytized wines – current perspectives

“…In other years, using terminal restriction fragment length polymorphism (RFLP) in the same wine type, the C. zemplinina population was not as pronounced at the beginning, although it was found to increase in the microbiota by the end of fermentation. 23 Long prevalence of C. zemplinina was also found in fermenting Tokaji Aszú, 38 Greek botrytized wine, 45 and passito wine. 36 Although C. zemplinina is known to be particularly associated with high sugar musts or wines, it is common on nonbotrytized grapes as well, although in lower populations.…”

“…or Kluyveromyces dobzhanskii, 45 are present and contribute to the fermentation, although to a lesser extent and for a shorter time than C. zemplinina in general. Several M. pulcherrima are capable of making a positive contribution to volatile thiol release (3SH) in wines, essentially during the prefermentation stage in winemaking, when this microbiological subpopulation is dominant.…”

“…48 Apart from C. zemplinina, a persistent dominance of Z. bailii throughout the fermentation was also reported in Botrytis-affected fermentation. 45 Being sugar tolerant and resistant to various chemical preservatives, this species is considered an important spoilage yeast in winemaking.…”

“…[40][41][42][43][44] In botrytized wine fermentation, C. zemplinina frequently initiates the spontaneous fermentation and survives long after Saccharomyces strains have begun to dominate, particularly at lower temperatures. 22,45 Its main contribution to the quality of botrytized wine is to lend a beneficial modification of the glucose-fructose ratio and enhance glycerol production. 38 Its importance in the aroma composition of Tokaji Aszú was not confirmed, 46 but seems significant in other wine styles.…”

Microbial Succession in Spontaneously Fermented Grape Must Before, During and After Stuck Fermentation

“…For a better understanding of the interactions between the different microorganisms, knowledge about the succession of the microbiota in the fermenting must is important. Saccharomyces cerevisiae was assigned to play a main role during the fermentation, although other organisms have been isolated from grape must (Du Toit & Lambrechts, 2002;Lopez et al, 2003;Nisioutou et al, 2007;Renouf et al, 2007;Lopandic et al, 2008). In general, non-Saccharomyces yeasts start the fermentation (high sugar concentration) and are substituted by S. cerevisiae strains when the alcohol concentration increases.…”