The Impact of Saccharomyces cerevisiae on a Wine Yeast Consortium in Natural and Inoculated Fermentations

Abstract

Natural, also referred to as spontaneous wine fermentations, are carried out by the native microbiota of the grape juice, without inoculation of selected, industrially produced yeast or bacterial strains. Such fermentations are commonly initiated by non-Saccharomyces yeast species that numerically dominate the must. Community composition and numerical dominance of species vary significantly between individual musts, but Saccharomyces cerevisiae will in most cases dominate the late stages of the fermentation and complete the process. Nevertheless, non-Saccharomyces species contribute significantly, positively or negatively, to the character and quality of the final product. The contribution is species and strain dependent and will depend on each species or strain's absolute and relative contribution to total metabolically active biomass, and will therefore, be a function of its relative fitness within the microbial ecosystem. However, the population dynamics of multispecies fermentations are not well understood. Consequently, the oenological potential of the microbiome in any given grape must, can currently not be evaluated or predicted. To better characterize the rules that govern the complex wine microbial ecosystem, a model yeast consortium comprising eight species commonly encountered in South African grape musts and an ARISA based method to monitor their dynamics were developed and validated. The dynamics of these species were evaluated in synthetic must in the presence or absence of S. cerevisiae using direct viable counts and ARISA. The data show that S. cerevisiae specifically suppresses certain species while appearing to favor the persistence of other species. Growth dynamics in Chenin blanc grape must fermentation was monitored only through viable counts. The interactions observed in the synthetic must, were upheld in the natural must fermentations, suggesting the broad applicability of the observed ecosystem dynamics. Importantly, the presence of indigenous yeast populations did not appear to affect the broad interaction patterns between the consortium species. The data show that the wine ecosystem is characterized by both mutually supportive and inhibitory species. The current study presents a first step in the development of a model to predict the oenological potential of any given wine mycobiome.

Keywords: ARISA; population dynamics; wine fermentation; yeast consortium; yeast interactions.

FIGURE 1

Electropherogram of a mixed culture of 18 yeast species, generated via PCR amplification with ITS1F-ITS4 primers. The x-axis represents the fragment size (bp) and the y-axis represents the relative fluorescence intensity. The following abbreviations were used for names of yeast species. Mp, Metschnikowia pulcherrima; Pt, Pichia terricola; Ca, Candida azyma; Sb, Starmerella bacillaris; Io, Issatchenkia orientalis; Cp, Candida parapsilosis; Lt, Lachancea thermotolerans; Hv, Hanseniaspora vineae; Ka, Kazachstania aerobia; Td, Torulaspora delbrueckii; Sc, Saccharomyces cerevisiae; Cg, Candida glabrata.

FIGURE 2

Quantitative validation between the ARISA peaks of eight selected yeast species and CFU/mL. All yeast species were inoculated at 10⁵ CFU/mL. The x-axis represents the fragment size (bp) and the y-axis represents the relative fluorescence intensity.

FIGURE 3

Standard curves of individual yeast species in the consortium. The correlation between the colony forming unit and peak area (bp) was investigated at different dilutions (10³–10⁷ CFU/mL) for individual yeast species in the consortium.

FIGURE 4

Progress curves showing the kinetics of fermentations performed in the synthetic must. Fermentation performed with NS-Sc consortium is indicated with broken lines while fermentation with NS consortium is indicated with solid lines. Glucose (■), fructose (▲) and CO₂ release (●) were monitored throughout fermentation.

FIGURE 5

Relative abundance of yeast species throughout the NS-Sc fermentation in synthetic grape must. Yeast population dynamics were monitored using ARISA and plating methods.

FIGURE 6

Growth profiles of yeast population throughout NS-Sc fermentation in the synthetic must.

FIGURE 7

Relative abundance of yeast species during fermentations performed with NS-Sc and NS. Yeast population dynamics was monitored using ARISA.

FIGURE 8

Progress curves displaying the kinetics of spontaneous fermentation (●), fermentation inoculated with Sc (), and fermentation inoculated with NS-Sc consortium ().

FIGURE 9

Yeast population dynamics in Chenin blanc spontaneous fermentation (A), S. cerevisiae inoculated fermentation (B) and NS-Sc consortium fermentation (C). The following abbreviations were used for names of yeast species. Mp, M. pulcherrima; It, P. terricola; Sb, S. bacillaris; Cp, C. parapsilosis; Lt, L. thermotolerans; Hv, H. vineae; Hu, H. uvarum; IND.Sc, Indigenous S. cerevisiae.