Pourcelot, E. | bioRxiv Science

bioRxiv2024

S. cerevisiae serves as keystone species for spoilage resistance in experimental synthetic wine yeast communities

Species diversity is a commonly stated contributor to the fate of an invader, and thus community resistance, in both microbial and non-microbial communities. Termed the "diversity-invasion hypothesis", a positive relationship between diversity and resistance to invasion is observed when an introduced species exhibits lower levels of survival in resident communities with higher species richness. The diversity-invasion hypothesis is an attractive perspective with convincing theory and examples, yet an "invasion paradox" of contrasting results means that a positive role of diversity against invasion is still not a certainty and under debate. In this study we investigated the relationship between resistance to invasion and resident community species richness versus species identity (i.e., keystone species). Using synthetic communities comprised of combinations of four wine yeasts (Saccharomyces cerevisiae, Lachancea thermotolerans, Torulaspora delbrueckii, Starmerella bacillaris), we tracked over 21 days the presence of introduced Brettanomyces bruxellensis spoilage yeast and Lactiplantibacillus plantarum lactic acid bacteria to ask the following: 1. Does yeast community species richness impact the establishment of B. bruxellensis yeast and L. plantarum bacteria during wine fermentation? 2. How does yeast species identity influence such establishment? We found that species identity rather than richness drove the prevention of establishment of B. bruxellensis and L. plantarum, with S. cerevisiae playing a critical keystone species role. Aside from spoilage prevention by S. cerevisiae, the four resident yeast species demonstrated a strict dominance ranking of competitive exclusion regardless of background community composition. Our research lends evidence against the commonly predicted positive relationship between species richness and resistance to invasion. Furthermore, as spontaneously fermented natural wines and diverse starter cultures gain popularity, our findings support a remaining importance of S. cerevisiae in preventing B. bruxellensis spoilage..

ecology↗

bioRxiv2024

Design of a new model yeast consortium for ecological studies of enological fermentation

Wine fermentation involves complex microbial communities of non-Saccharomyces yeast species besides the well-known Saccharomyces cerevisiae. While extensive research has enhanced our understanding of S. cerevisiae, the development of multi-species fermentation starters has led to increased interest in yeast interactions and the role of microbial diversity in winemaking. Consequently, molecular methods have emerged to identify the different species at different stages of the winemaking process. Model microbial communities or consortia, which provide simplified systems resembling natural microbial diversity, offer opportunities to investigate population dynamics and understand the role of community diversity in ecosystem performance. Here, this work aims to design a yeast consortium reflecting the diversity of wine yeasts and to develop a method for accurately tracking their population dynamics during fermentation. We developed and characterized a six-species consortium, with S. cerevisiae, Hanseniaspora uvarum, Starmerella bacillaris, Metschnikowia pulcherrima, Lachancea thermotolerans and Torulaspora delbrueckii. By tagging each yeast species with distinct fluorescent markers, the study enables real-time monitoring of individual species within the consortium using flow cytometry. We have carried out a complete analysis of this consortium, studying the evolution of populations over time and examining factors such as metabolite production and fermentation kinetics. In addition, the yeast consortium was used to test the diversity-function relationship as a proof of concept. We sought to determine the impact of the initial evenness on communities performances subjected to osmotic stress. To this end, ten randomly designed consortia with varying initial species proportions were followed in enological fermentation with 200 and 280 g/L of initial sugars. The initial proportion of certain species affected the population dynamics and metabolite production however no demonstrable effect of the initial evenness on the response to osmotic stress was shown. These results demonstrated the usefulness of the presented consortium, which is now available to the scientific community and can contribute to future work trying to decipher multispecies dynamics and the role of yeast diversity in wine fermentation.

microbiology↗