Competition for Nitrogen Resources: An Explanation of the Effects of a Bioprotective Strain Metschnikowia pulcherrima on the Growth of Hanseniaspora Genus in Oenology

As a biological alternative to the antimicrobial action of SO2, bioprotection has been proposed to winemakers as a means to limit or prevent grape musts microbial alteration. Competition for nitrogenous nutrients and for oxygen are often cited as potential explanations for the effectiveness of bioprotection. This study analyses the effect of a bioprotective M. pulcherrima strain on the growth of one H. valbyensis strain and one H. uvarum strain. Bioprotection efficiency was observed only against H. valbyensis inoculated at the two lowest concentrations. These results indicate a potential species-dependent efficiency of the bioprotective strain and a strong impact of the initial ratio between bioprotective and apiculate yeasts. The analysis of the consumption of nitrogen compounds revealed that leucine, isoleucine, lysine and tryptophan were consumed preferentially by all three strains. The weaker assimilation percentages of these amino acids observed in H. valbyensis at 24 h growth suggest competition with M. pulcherrima that could negatively affects the growth of the apiculate yeast in co-cultures. The slowest rate of O2 consumption of H. valbyensis strain, in comparison with M. pulcherrima, was probably not involved in the bioprotective effect. Non-targeted metabolomic analyses of M. pulcherrima and H. valbyensis co-culture indicate that the interaction between both strains particularly impact lysin and tryptophan metabolisms.

Exploring future applications of the apiculate yeast Hanseniaspora

As a metaphor, lemons get a bad rap; however the proverb 'if life gives you lemons, make lemonade' is often used in a motivational context. The same could be said of Hanseniaspora in winemaking. Despite its predominance in vineyards and grape must, this lemon-shaped yeast is underappreciated in terms of its contribution to the overall sensory profile of fine wine. Species belonging to this apiculate yeast are known for being common isolates not just on grape berries, but on many other fruits. They play a critical role in the early stages of a fermentation and can influence the quality of the final product. Their deliberate addition within mixed-culture fermentations shows promise in adding to the complexity of a wine and thus provide sensorial benefits. Hanseniaspora species are also key participants in the fermentations of a variety of other foodstuffs ranging from chocolate to apple cider. Outside of their role in fermentation, Hanseniaspora species have attractive biotechnological possibilities as revealed through studies on biocontrol potential, use as a whole-cell biocatalyst and important interactions with Drosophila flies. The growing amount of 'omics data on Hanseniaspora is revealing interesting features of the genus that sets it apart from the other Ascomycetes. This review collates the fields of research conducted on this apiculate yeast genus.

Pantothenate Auxotrophy in a Naturally Occurring Biocontrol Yeast

The genus Hanseniaspora is characterized by some of the smallest genomes among budding yeasts. These fungi are primarily found on plant surfaces and in fermented products and represent promising biocontrol agents against notorious fungal plant pathogens. In this work, we identify pantothenate auxotrophy of a Hanseniaspora meyeri isolate that shows strong antagonism against the plant pathogen Fusarium oxysporum. Furthermore, strong biocontrol activity in vitro required both pantothenate and biotin in the growth medium. We show that the H. meyeri isolate APC 12.1 can obtain the vitamin from plants and other fungi. The underlying reason for the auxotrophy is the lack of two key pantothenate biosynthesis genes, but six genes encoding putative pantothenate transporters are present in the genome. By constructing and using a Saccharomyces cerevisiae reporter strain, we identified one Hanseniaspora transporter that conferred pantothenate uptake activity to S. cerevisiae. Pantothenate auxotrophy is rare and has been described in only a few bacteria and in S. cerevisiae strains that were isolated from sake. Such auxotrophic strains may seem an unexpected and unlikely choice as potential biocontrol agents, but they may be particularly competitive in their ecological niche and their specific growth requirements are an inherent biocontainment strategy preventing uncontrolled growth in the environment. Auxotrophic strains, such as the H. meyeri isolate APC 12.1, may thus represent a promising strategy for developing biocontrol agents that will be easier to register than prototrophic strains, which are normally used for such applications. IMPORTANCE As a precursor of the essential coenzyme A (CoA), pantothenate is present in all organisms. Plants, bacteria, and fungi are known to synthesize this vitamin, while animals must obtain it through their diet. Pantothenate auxotrophy has not been described in naturally occurring, environmental fungi and is an unexpected property for an antagonistic yeast. Here, we report that yeasts from the genus Hanseniaspora lack key enzymes for pantothenate biosynthesis and identify a transporter responsible for the acquisition of pantothenate from the environment. Hanseniaspora isolates are strong antagonists of fungal plant pathogens. Their pantothenate auxotrophy is a natural biocontainment feature that could make such isolates interesting candidates for new biocontrol approaches and allow easier registration as plant protection agents than prototrophic strains.

Ecology and population dynamics of yeast starter cultures in cocoa beans fermentation

This study aimed to investigate controlled fermentation of cocoa beans with selected yeasts as starter cultures via integrating microbiological, biochemical, and chromatographic analyses. The steps involved in the yeast starter culture test were of the following order: 1) counting, isolation, purification, and biochemical identification of yeasts, 2) selection of ethanol-producing yeasts, 3) selection of thermotolerant yeasts, and 4) evaluation of physicochemical parameters of the selected yeasts in controlled fermentation of cocoa (F1 - Saccharomyces ssp. and Hanseniaspora ssp. and F2 - spontaneous fermentation - control). A total of 32 yeasts were isolated from three sampling points (M1, M2, and M3), which comprised 50% Candida ssp., 9.4% Rhodotorula ssp., 18.8% Saccharomyces ssp., and 18.8% Hanseniaspora ssp. The yeasts identified as Saccharomyces ssp. (n = 6) were subjected to the ethanol production test. Saccharomyces spp. CLV09 showed the highest concentration of ethanol in the simulated cocoa medium (3.5% v/v). Hanseniaspora spp. CVL20 and CVL19 strains showed the highest thermotolerance at 42°C after 72 h of growth. The starter cultures with Saccharomyces ssp. and Hanseniaspora ssp. showed a similar growth rate of the mesophilic aerobic population in both F1 and F2. Fermentation of the starter culture showed a higher production of organic acids than spontaneous fermentation (F2). Thus, Saccharomyces ssp. and Hanseniaspora ssp. can be used as a starter culture in cocoa fermentation.

Synthesis of Aroma Compounds as a Function of Different Nitrogen Sources in Fermentations Using Non-Saccharomyces Wine Yeasts

Non-Saccharomyces yeasts are prevalent at the onset of grape must fermentations and can have a significant influence on the final wine product. In contrast to Saccharomyces cerevisiae, the biosynthetic pathways leading to aroma compound formation in these non-conventional yeasts, in particular those that are derived from amino acid metabolism, remains largely unexplored. Within a synthetic must environment, we investigated the amino acid utilization of four species (Hanseniaspora uvarum, Hanseniaspora osmophila, Zygosaccharomyces rouxii, Starmerella bacillaris) and S. cerevisiae. We report on the differential uptake preferences for amino acids with H. uvarum displaying the most rapid uptake of most amino acids. To investigate the fate of amino acids and their direct contribution to aroma synthesis in H. uvarum, H. osmophila and Z. rouxii, musts were supplemented with single amino acids. Aroma profiling undertaken after three days showed the synthesis of specific aroma compounds by the respective yeast was dependent on the specific amino acid supplementation. H. osmophila showed similarities to S. cerevisiae in both amino acid uptake and the synthesis of aroma compounds depending on the nitrogen sources. This study shows how the uptake of specific amino acids contributes to the synthesis of aroma compounds in wine fermentations using different non-Saccharomyces yeasts.

Wine yeast selection in the Iberian Peninsula: Saccharomyces and non-Saccharomyces as drivers of innovation in Spanish and Portuguese wine industries

Yeast selection for the wine industry in Spain started in 1950 for the understanding of the microbial ecology, and for the selection of optimal strains to improve the performance of alcoholic fermentation and the overall wine quality. This process has been strongly developed over the last 30 years, firstly on Saccharomyces cerevisiae, and, lately, with intense activity on non-Saccharomyces. Several thousand yeast strains have been isolated, identified and tested to select those with better performance and/or specific technological properties. The present review proposes a global survey of this massive ex-situ preservation of eukaryotic microorganisms, a reservoir of biotechnological solutions for the wine sector, overviewing relevant screenings that led to the selection of strains from 12 genera and 22 species of oenological significance. In the first part, the attention goes to the selection programmes related to relevant wine-producing areas (i.e. Douro, Extremadura, Galicia, La Mancha and Uclés, Ribera del Duero, Rioja, Sherry area, and Valencia). In the second part, the focus shifted on specific non-Saccharomyces genera/species selected from different Spanish and Portuguese regions, exploited to enhance particular attributes of the wines. A fil rouge of the dissertation is the design of tailored biotechnological solutions for wines typical of given geographic areas.

Native yeast and non-yeast fungal communities of Cabernet Sauvignon berries from two Washington State vineyards, and persistence in spontaneous fermentation

To address a knowledge gap about the grape berry mycobiome from Washington State vineyards, next-generation sequencing of the internal transcribed spacer region (ITS1) was used to identify native yeast and fungal species on berries of cultivar 'Cabernet Sauvignon' from two vineyards at veraison and harvest in 2015 and 2016. Four hundred fifty-six different yeast amplicon sequence variants (ASV), representing 184 distinct taxa, and 2467 non-yeast fungal ASV (791 distinct taxa) were identified in this study. A set of 50 recurrent yeast taxa, including Phaeococcomyces, Vishniacozyma and Metschnikowia, were found at both locations and sampling years. These yeast species were monitored from the vineyard into laboratory-scale spontaneous fermentations. Taxa assignable to Metschnikowia and Saccharomyces persisted during fermentation, whereas Curvibasidium, which also has possible impact on biocontrol and wine quality, did not. Sulfite generally reduced yeast diversity and richness, but its effect on the abundance of specific yeasts during fermentation was negligible. Among the 106 recurring non-yeast fungal taxa, Alternaria, Cladosporium and Ulocladium were especially abundant in the vineyard. Vineyard location was the primary factor that accounted for the variation among both communities, followed by year and berry developmental stage. The Washington mycobiomes were compared to those from other parts of the world. Sixteen recurrent yeast species appeared to be unique to Washington State vineyards. This subset also contained a higher proportion of species associated with cold and extreme environments, relative to other localities. Certain yeast and non-yeast fungal species known to suppress diseases or modify wine sensory properties were present in Washington vineyards, and likely have consequences to vineyard health and wine quality.

nov., an ascomycetous yeast isolated from Tibet

Eight apiculate strains isolated from Tibet, PR China, were identified as Hanseniaspora taiwanica and a novel species of Hanseniaspora based on the sequence analysis of the ITS region, the D1/D2 domains of the LSU rRNA and the translation elongation factor 1-a (TEF1) gene. Among them, four strains with identical sequences of D1/D2 and ITS formed a separate branch from the known Hanseniaspora species in the phylogenetic trees, and differed from the known species by at least 17 (3 %) nucleotide (nt) substitutions in the D1/D2 domains and more than 6 % substitutions and inserts/deletes in the ITS region. The phylogenetic analysis indicated that those four strains represent a novel species of Hanseniaspora, for which the names Hanseniaspora terricola sp. nov. (holotype CGMCC 2.6175^T; MycoBank MB 834591) is proposed. The other four strains belonging to H. taiwanica produce spherical, void or fusiform ascospores, which differ from the original description that ascospores are absent.

How gut microbiome interactions affect nutritional traits of Drosophila melanogaster

Most research on the impact of the gut microbiome on animal nutrition is designed to identify the effects of single microbial taxa and single metabolites of microbial origin, without considering the potentially complex network of interactions among co-occurring microorganisms. Here, we investigated how different microbial associations and their fermentation products affect host nutrition, using Drosophila melanogaster colonized with three gut microorganisms (the bacteria Acetobacter fabarum and Lactobacillus brevis, and the yeast Hanseniaspora uvarum) in all seven possible combinations. Some microbial effects on host traits could be attributed to single taxa (e.g. yeast-mediated reduction of insect development time), while other effects were sex specific and driven by among-microbe interactions (e.g. male lipid content determined by interactions between the yeast and both bacteria). Parallel analysis of nutritional indices of microbe-free flies administered different microbial fermentation products (acetic acid, acetoin, ethanol and lactic acid) revealed a single consistent effect: that the lipid content of both male and female flies is reduced by acetic acid. This effect was recapitulated in male flies colonized with both yeast and A. fabarum, but not for any microbial treatment in females or males with other microbial complements. These data suggest that the effect of microbial fermentation products on host nutritional status is strongly context dependent, with respect to both the combination of associated microorganisms and host sex. Taken together, our findings demonstrate that among-microbe interactions can play a critically important role in determining the physiological outcome of host-microbiome interactions in Drosophila and, likely, in other animal hosts.

Genome-wide identification, characterization and expression analysis of lineage-specific genes within Hanseniaspora yeasts

Lineage-specific genes (LSGs) are defined as genes with sequences that are not significantly similar to those in any other lineage. LSGs have been proposed, and sometimes shown, to have significant effects in the evolution of biological function. In this study, two sets of Hanseniaspora spp. LSGs were identified by comparing the sequences of the Kloeckera apiculata genome and of 80 other yeast genomes. This study identified 344 Hanseniaspora-specific genes (HSGs) and 109 genes ('orphan genes') specific to K. apiculata. Three thousand three hundred thirty-one K. apiculata genes that showed significant similarity to at least one sequence outside the Hanseniaspora were classified into evolutionarily conserved genes. We analyzed their sequence features, functional categories, gene origin, gene structure and gene expression. We also investigated the predicted cellular roles and Gene Ontology categories of the LSGs using functional inference. The patterns of the functions of LSGs do not deviate significantly from genome-wide average. The results showed that a few LSGs were formed by gene duplication, followed by rapid sequence divergence. Many of the HSGs and orphan genes exhibited altered expression in response to abiotic stress. Studying these LSGs might be helpful for understanding the molecular mechanism of yeast adaption.

Into the wild: new yeast genomes from natural environments and new tools for their analysis

Genomic studies of yeasts from the wild have increased considerably in the past few years. This revolution has been fueled by advances in high-throughput sequencing technologies and a better understanding of yeast ecology and phylogeography, especially for biotechnologically important species. The present review aims to first introduce new bioinformatic tools available for the generation and analysis of yeast genomes. We also assess the accumulated genomic data of wild isolates of industrially relevant species, such as Saccharomyces spp., which provide unique opportunities to further investigate the domestication processes associated with the fermentation industry and opportunistic pathogenesis. The availability of genome sequences of other less conventional yeasts obtained from the wild has also increased substantially, including representatives of the phyla Ascomycota (e.g. Hanseniaspora) and Basidiomycota (e.g. Phaffia). Here, we review salient examples of both fundamental and applied research that demonstrate the importance of continuing to sequence and analyze genomes of wild yeasts.

Two Gut-Associated Yeasts in a Tephritid Fruit Fly have Contrasting Effects on Adult Attraction and Larval Survival

Yeast-insect interactions have been well characterized in drosophilid flies, but not in tephritid fruit flies, which include many highly polyphagous pest species that attack ripening fruits. Using the Queensland fruit fly (Bactrocera tryoni) as our model tephritid species, we identified yeast species present in the gut of wild-collected larvae and found two genera, Hanseniaspora and Pichia, were the dominant isolates. In behavioural trials using adult female B. tryoni, a fruit-agar substrate inoculated with Pichia kluyveri resulted in odour emissions that increased the attraction of flies, whereas inoculation with Hanseniaspora uvarum, produced odours that strongly deterred flies, and both yeasts led to decreased oviposition. Larval development trials showed that the fruit-agar substrate inoculated with the 'deterrent odour' yeast species, H. uvarum, resulted in significantly faster larval development and a greater number of adult flies, compared to a substrate inoculated with the 'attractive odour' yeast species, P. kluyveri, and a yeast free control substrate. GC-MS analysis of volatiles emitted by H. uvarum and P. kluyveri inoculated substrates revealed significant quantitative differences in ethyl-, isoamyl-, isobutyl-, and phenethyl- acetates, which may be responsible for the yeast-specific olfactory responses of adult flies. We discuss how our seemingly counterintuitive finding that female B. tryoni flies avoid a beneficial yeast fits well with our understanding of female choice of oviposition sites, and how the contrasting behavioural effects of H. uvarum and P. kluyveri raises interesting questions regarding the role of yeast-specific volatiles as cues to insect vectors. A better understanding of yeast-tephritid interactions could assist in the future management of tephritid fruit fly pests through the formulation of new "attract and kill" lures, and the development of probiotics for mass rearing of insects in sterile insect control programs.

Sequential Inoculation of Native Non-Saccharomyces and Saccharomyces cerevisiae Strains for Wine Making

The use of non-Saccharomyces yeast for wine making is becoming a common trend in many innovative wineries. The application is normally aimed at increasing aromas, glycerol, reducing acidity, and other improvements. This manuscript focuses on the reproduction of the native microbiota from the vineyard in the inoculum. Thus, native selected yeasts (Hanseniaspora uvarum, Metschnikowia pulcherrima, Torulaspora delbrueckii, Starmerella bacillaris species and three different strains of Saccharomyces cerevisiae) were inoculated sequentially, or only S. cerevisiae (three native strains together or one commercial) was used. Inoculations were performed both in laboratory conditions with synthetic must (400 mL) as well as in industrial conditions (2000 kg of grapes) in red winemaking in two different varieties, Grenache and Carignan. The results showed that all the inoculated S. cerevisiae strains were found at the end of the vinifications, and when non-Saccharomyces yeasts were inoculated, they were found in appreciable populations at mid-fermentation. The final wines produced could be clearly differentiated by sensory analysis and were of similar quality, in terms of sensory analysis panelists' appreciation.

Yeasts Harbored by Vespine Wasps in the Pacific Northwest

The ecological role of social wasps has been extensively studied, but little is known about symbiotic relationships of these wasps with microbes. Recently, it was shown that vespid wasps in Europe carry yeasts, predominantly Saccharomyces cerevisiae, in their gastrointestinal (GI) tract. Interestingly, this niche allowed for sexual recombination of yeasts to occur and the formation of novel hybrid species. Our goals were 1) to survey the GI tract of eusocial wasps in the Pacific Northwest for the presence of yeasts and 2) to compare the diversity of such yeasts to that described for wasps in Europe. The GI tracts of 19 individual wasps from five species were plated, and 27 yeast-like colonies were identified to the species level. Yeasts in the genera Lachancea and Hanseniaspora each comprised ∼30% of the isolates; ∼25% were identified as Metschnikowia spp., with the remaining 10% belonging to Rhodotorula. Four bacterial isolates were identified as Escherichia coli, Enterococcus faecalis, and two isolates of Stenotrophomonas maltophilia. Yeasts were present at all life stages of the wasps except for two unfed gynes of Dolichovespula maculata (L.) that contained only bacteria. The presence of a particular yeast species was not correlated with any wasp species. Furthermore, S. cerevisiae was not found in any wasp species. This highlights an interesting difference in the life cycle of both S. cerevisiae and wasps in Europe and the Pacific Northwest, and prompts further studies on the interactions of these microbes with their host wasps.

Saccharomyces and non-Saccharomyces Competition during Microvinification under Different Sugar and Nitrogen Conditions

The inoculation of wines with autochthonous yeast allows obtaining complex wines with a peculiar microbial footprint characteristic from a wine region. Mixed inoculation of non-Saccharomyces yeasts and S. cerevisiae is of interest for the wine industry for technological and sensory reasons. However, the interactions between these yeasts are not well understood, especially those regarding the availability of nutrients. The aim of the present study was to analyze the effect of nitrogen and sugar concentration on the evolution of mixed yeast populations on controlled laboratory-scale fermentations monitored by density, plate culturing, PCR-DGGE and sugar and nitrogen consumption. Furthermore, the effect of the time of inoculation of Saccharomyces cerevisiae respect the initial co-inoculation of three non-Saccharomyces yeasts was evaluated over the evolution of fermentation. Our results have shown that S. cerevisiae inoculation during the first 48 h conferred a stabilizing effect over the fermentations with non-Saccharomyces strains tested and, generally, reduced yeast diversity at the end of the fermentation. On the other hand, nitrogen limitation increased the time of fermentation and also the proportion of non-Saccharomyces yeasts at mid and final fermentation. High sugar concentration resulted in different proportions of the inoculated yeast depending on the time of S. cerevisiae inoculation. This work emphasizes the importance of the concentration of nutrients on the evolution of mixed fermentations and points to the optimal conditions for a stable fermentation in which the inoculated yeasts survived until the end.

Microbial Terroir in Chilean Valleys: Diversity of Non-conventional Yeast

In this study, the presence of non-conventional yeast associated with vineyards located between latitudes 30°S and 36°S was examined, including the valleys of Limarí, Casablanca, Maipo, Colchagua, Maule, and Itata. The microbial fingerprinting in each valley was examined based on the specific quantification of yeast of enological interest. Grape–berries were sampled to evaluate the presence and load of non-conventional yeast with enological potential, such as Metschnikowia, Hanseniaspora, Torulaspora, Debaryomyces, Meyerozyma, and Rhodotorula. These yeasts were present in all vineyards studied but with varying loads depending on the valley sampled. No identical fingerprints were observed; however, similarities and differences could be observed among the microbial profiles of each valley. A co-variation in the loads of Metschnikowia and Hanseniaspora with latitude was observed, showing high loads in the Casablanca and Itata valleys, which was coincident with the higher relative humidity or rainfall of those areas. Non-conventional yeasts were also isolated and identified after sequencing molecular markers. Potentially good aromatic properties were also screened among the isolates, resulting in the selection of mostly Metschnikowia and Hanseniaspora isolates. Finally, our results suggest that microbial terroir might be affected by climatic conditions such as relative humidity and rainfall, especially impacting the load of non-conventional yeast. In this study, the microbial fingerprint for yeast in Chilean vineyards is reported for the first time revealing an opportunity to study the contribution of this assembly of microorganisms to the final product.

Comparison of Fermentation and Wines Produced by Inoculation of Hanseniaspora vineae and Saccharomyces cerevisiae

Interest in the use of non-Saccharomyces yeasts in winemaking has been increasing due to their positive contributions to wine quality. The non-Saccharomyces yeast Hanseniaspora vineae is an apiculate yeast that has been associated with the production of wine with good aromatic properties. However, little is known about the fermentation dynamics of H. vineae in natural must and its interaction with autochthonous yeasts. In the present study, we performed semi industrial fermentations of Macabeo and Merlot musts inoculated with either H. vineae or S. cerevisiae. The yeast population dynamics were monitored by plate culturing, PCR-DGGE and massive sequencing techniques. The results obtained with these techniques show that H. vineae was able dominate the autochthonous microbiota in Macabeo must but not in Merlot must, which exhibited a larger, more diverse yeast population. The presence of H. vineae throughout most of the Macabeo fermentation resulted in more fruity and flowery wine, as indicated by the chemical analysis of the final wines, which demonstrated a strong presence of phenyl ethyl acetate at concentrations higher than the threshold of perception and approximately 50 times more than that produced in wines fermented with S. cerevisiae. This compound is associated with fruity, floral and honey aromas.

Persistence of Two Non-Saccharomyces Yeasts (Hanseniaspora and Starmerella) in the Cellar

Different genera and/or species of yeasts present on grape berries, in musts and wines are widely described. Nevertheless, the community of non-Saccharomyces yeasts present in the cellar is still given little attention. Thus it is not known if the cellar is a real ecological niche for these yeasts or if it is merely a transient habitat for populations brought in by grape berries during the winemaking period. This study focused on three species of non-Saccharomyces yeasts commonly encountered during vinification: Starmerella bacillaris (synonymy with Candida zemplinina), Hanseniaspora guilliermondii and Hanseniaspora uvarum. More than 1200 isolates were identified at the strain level by FT-IR spectroscopy (207 different FTIR strain pattern). Only a small proportion of non-Saccharomyces yeasts present in musts came directly from grape berries for the three species studied. Some strains were found in the must in two consecutive years and some of them were also found in the cellar environment before the arrival of the harvest of second vintage. This study demonstrates for the first time the persistence of non-Saccharomyces yeast strains from year to year in the cellar. Sulfur dioxide can affect yeast populations in the must and therefore their persistence in the cellar environment.

Diversity of yeast strains of the genus Hanseniaspora in the winery environment: What is their involvement in grape must fermentation?

Isolated yeast populations of Chardonnay grape must during spontaneous fermentation were compared to those isolated on grape berries and in a winery environment before the arrival of the harvest (air, floor, winery equipment) and in the air through time. Two genera of yeast, Hanseniaspora and Saccharomyces, were isolated in grape must and in the winery environment before the arrival of the harvest but not on grape berries. The genus Hanseniaspora represented 27% of isolates in the must and 35% of isolates in the winery environment. The isolates of these two species were discriminated at the strain level by Fourier transform infrared spectroscopy. The diversity of these strains observed in the winery environment (26 strains) and in must (12 strains) was considerable. 58% of the yeasts of the genus Hanseniaspora isolated in the must corresponded to strains present in the winery before the arrival of the harvest. Although the proportion and number of strains of the genus Hanseniaspora decreased during fermentation, some strains, all from the winery environment, subsisted up to 5% ethanol content. This is the first time that the implantation in grape must of populations present in the winery environment has been demonstrated for a non-Saccharomyces genus.

Oenological prefermentation practices strongly impact yeast population dynamics and alcoholic fermentation kinetics in Chardonnay grape must

Yeast species of Hanseniaspora and Candida genus are predominant during the early stages of winemaking, while species of Metschnikowia, Pichia, Zygoascus, Issatchenkia, Torulaspora and other genera are present at lower population levels. The impact of common oenological practices on yeast dynamics during the prefermentative stage and the early stage of alcoholic fermentation (AF) remains elusive. In this work, the effect of four prefermentative oenological practices (clarification degree, temperature, sulphite and starter yeast addition) on yeast dynamics was evaluated in a Chardonnay grape must. The growth curves of four genus or species, namely Saccharomyces spp., Hanseniaspora spp., Candida zemplinina and Torulaspora delbrueckii, were followed by quantitative PCR. The fermentation kinetics were also recorded, as well as the production of acetic acid. Variance analysis allowed determining the effect of each practice and their interaction factors, as well as their relative importance on yeast dynamics and fermentation kinetics. Our experimental design showed that the population dynamics of the four species were differently impacted by the oenological practices, with some species being more sensitive than others to the clarification degree (C. zemplinina), sulphite addition (Saccharomyces spp.), starter yeast inoculation (Hanseniaspora spp.) or prefermentation temperature (T. delbrueckii). Significant interaction effects between practices were revealed, highlighting the interest of experimental design allowing interaction analysis, as some factors may buffer the effect of other ones. Hanseniaspora genus showed atypical behaviour: growth dynamics showed a decrease during AF that we interpreted as early cellular lysis. In conclusion, this study provides new insights on the impact of common oenological practices on the dynamics of non-Saccharomyces yeast that will be useful for a better management of mixed fermentation between S. cerevisiae and non-Saccharomyces yeasts.