Insights into the ecology of Schizosaccharomyces species in natural and artificial habitats

The fission yeast genus Schizosaccharomyces contains important model organisms for biological research. In particular, S. pombe is a widely used model eukaryote. So far little is known about the natural and artificial habitats of species in this genus. Finding out where S. pombe and other fission yeast species occur and how they live in their habitats can promote better understanding of their biology. Here we investigate in which substrates S. pombe, S. octosporus, S. osmophilus and S. japonicus are present. To this end about 2100 samples consisting of soil, tree sap fluxes, fresh fruit, dried fruit, honey, cacao beans, molasses and other substrates were analyzed. Effective isolation methods that allow efficient isolation of the above mentioned species were developed. Based on the frequency of isolating different fission yeast species in various substrates and on extensive literature survey, conclusions are drawn on their ecology. The results suggest that the primary habitat of S. pombe and S. octosporus is honeybee honey. Both species were also frequently detected on certain dried fruit like raisins, mango or pineapple to which they could be brought by the honey bees during ripening or during drying. While S. pombe was regularly isolated from grape mash and from fermented raw cacao beans S. octosporus was never isolated from fresh fruit. The main habitat of S. osmophilus seems to be solitary bee beebread. It was rarely isolated from raisins. S. japonicus was mainly found in forest substrates although it occurs on fruit and in fruit fermentations, too.

Lebanon's Native Oenological Saccharomyces cerevisiae Flora: Assessment of Different Aspects of Genetic Diversity and Evaluation of Winemaking Potential

A total of 296 isolates of Saccharomyces cerevisiae sampled from naturally fermenting grape musts from various locations in Lebanon were typed by interdelta fingerprinting. Of these, 88 isolates were compared with oenological strains originating from various countries, using microsatellite characterization at six polymorphic loci. These approaches evidenced a large diversity of the natural oenological Lebanese flora over the territory as well as in individual spontaneous fermentations. Several cases of dominance and perenniality of isolates were observed in the same wineries, where fermentations appeared to involve lineages of sibling isolates. Our work thus evidenced a “winery effect” on strains’ relatedness. Similarly, related or identical strains were also detected in vicinal wineries, suggesting strain circulation within small geographical areas and a further “vicinity effect”. Moreover, and despite its diversity, the Lebanese flora seemed interrelated, on the basis of microsatellite loci analysis, in comparison to worldwide communities. We finally tested the ability of 21 indigenous strains to act as potential starters for winemaking. Seven of them passed our pre-selection scheme and two of them at least may be good candidates for use provided pilot-scale assays confirm their suitability.

Vinification without Saccharomyces: Interacting Osmotolerant and "Spoilage" Yeast Communities in Fermenting and Ageing Botrytised High-Sugar Wines (Tokaj Essence)

The conversion of grape juice to wine starts with complex yeast communities consisting of strains that have colonised the harvested grape and/or reside in the winery environment. As the conditions in the fermenting juice gradually become inhibitory for most species, they are rapidly overgrown by the more adaptable Saccharomyces strains, which then complete the fermentation. However, there are environmental factors that even Saccharomyces cannot cope with. We show that when the sugar content is extremely high, osmotolerant yeasts, usually considered as “spoilage yeasts“, ferment the must. The examination of the yeast biota of 22 botrytised Tokaj Essence wines of sugar concentrations ranging from 365 to 752 g∙L⁻¹ identified the osmotolerant Zygosaccharomyces rouxii, Candida (Starmerella) lactis-condensi and Candida zemplinina (Starmerella bacillaris) as the dominating species. Ten additional species, mostly known as osmotolerant spoilage yeasts or biofilm-producing yeasts, were detected as minor components of the populations. The high phenotypical and molecular (karyotype, mtDNA restriction fragment length polymorphism (RFLP) and microsatellite-primed PCR (MSP-PCR)) diversity of the conspecific strains indicated that diverse clones of the species coexisted in the wines. Genetic segregation of certain clones and interactions (antagonism and crossfeeding) of the species also appeared to shape the fermenting yeast biota.

Modulating Wine Pleasantness Throughout Wine-Yeast Co-Inoculation or Sequential Inoculation

Wine sensory experience includes flavor, aroma, color, and (for some) even acoustic traits, which impact consumer acceptance. The quality of the wine can be negatively impacted by the presence of off-flavors and aromas, or dubious colors, or sediments present in the bottle or glass, after pouring (coloring matter that precipitates or calcium bitartrate crystals). Flavor profiles of wines are the result of a vast number of variations in vineyard and winery production, including grape selection, winemaker’s knowledge and technique, and tools used to produce wines with a specific flavor. Wine color, besides being provided by the grape varieties, can also be manipulated during the winemaking. One of the most important “tools” for modulating flavor and color in wines is the choice of the yeasts. During alcoholic fermentation, the wine yeasts extract and metabolize compounds from the grape must by modifying grape-derived molecules, producing flavor-active compounds, and promoting the formation of stable pigments by the production and release of fermentative metabolites that affect the formation of vitisin A and B type pyranoanthocyanins. This review covers the role of Saccharomyces and non-Saccharomyces yeasts, as well as lactic acid bacteria, on the perceived flavor and color of wines and the choice that winemakers can make by choosing to perform co-inoculation or sequential inoculation, a choice that will help them to achieve the best performance in enhancing these wine sensory qualities, avoiding spoilage and the production of defective flavor or color compounds.

The impact of active dry yeasts in commercial wineries from the Denomination of Origen "Vinos de Madrid", Spain

This paper has studied the success of implantation for 16 commercial active dry yeasts (ADYs) during industrial fermentation (30) and the impact of these yeasts during spontaneous fermentations (19) in 10 wineries from the Denomination of Origin "Vinos de Madrid" over two consecutive years. Yeasts strains were identified by molecular techniques, pulsed field electrophoresis and microsatellite analysis. According to these techniques, all the ADYs were different with the exceptions of two strains, L2056 and Rh, which showed the same karyotype and loci size. The results showed that inoculating fermentations with ADYs did not ensure their dominance throughout the fermentation; the implantation level of ADYs was above 80% in only 9 of the 30 commercial fermentations studied; while in 16 fermentations, the dominance of the inoculated ADYs was below 50%. The type of vinification with the best implantation results overall were those associated with red wine fermentations. ADYs affected spontaneous fermentations, although their impact was observed to decrease in the second year of the study. Therefore, specific adaptation studies are necessary before using commercial yeasts during the fermentation process. At the same time, a study was carried out on the frequency of commercial strains in IMIDRA's yeast collection, made up of strains isolated from spontaneous fermentations of the different areas and cellars since the beginning of the Denomination of Origin "Vinos de Madrid" in 1990. Six different ADYs were found with a frequency of less than 5%.

Effects of Pure and Mixed Autochthonous Torulaspora delbrueckii and Saccharomyces cerevisiae on Fermentation and Volatile Compounds of Narince Wines

The cultivar of Narince is a native white grape variety of Vitis vinifera, grown in Tokat city, the Mid-Black Sea Region of Anatolia. In this study, the effects of pure and mixed autochthonous Torulaspora delbrueckii-214 and Saccharomyces cerevisiae-1088 cultures on the fermentation behavior and aroma compounds of Narince wines were investigated. Volatile compounds formed in wines were extracted using a liquid–liquid extraction method and determined by GC-MS-FID. Narince grape must was fermented in duplicate, under the following three conditions. Two pure cultures of T. delbrueckii-214 and S. cerevisiae-1088 and a mixture of T. delbrueckii-214 and S. cerevisiae-1088 (1:1). The presence of the non-Saccharomyces T. delbrueckii-214 yeast slowed down the fermentation and produced a lower level of ethanol and a higher levels of glycerol and volatile acid. Only the pure culture of T. delbrueckii-214 was unable to finish fermentation. On the other hand, mixed culture fermentation improved the aroma intensity and complexity of wine due to increased levels of higher alcohols and esters. According to sensory analysis, wine fermented with mixed culture was the most preferred wine followed by wine inoculated with pure S. cerevisiae-1088. This study confirms the role of T. delbrueckii in wine aroma and the potential of non-Saccharomyces use in winemaking.

The Different Physical and Chemical Composition of Grape Juice and Marc Influence Saccharomyces cerevisiae Strains Distribution During Fermentation

During white-grape winemaking, grape marc is separated from juice immediately after crushing. Both mark and juice are obtained from the same grapes, but they differ strongly for their physical and chemical properties. Marc is mainly composed of solid residues. Its pH is usually higher than that of the juice and Saccharomyces cerevisiae strains are largely present. Therefore, it can be considered as a potential alternative environment for the selection of industrial yeasts. In order to evaluate the effect of different pH and physical state of the two matrices on grapes yeast population composition, the isolation of S. cerevisiae, from both grape juice and marc during simultaneous fermentations, was performed. After yeast identification and genotyping, strains present at high frequencies were tested in fermentation at different pH values. Biofilm production was also tested to evaluate strain ability to develop on a solid matrix. Genotype analysis showed that high-frequency strains were always more abundant in one of the two environments, suggesting the existence of a selective effect. Generally, fermentations at different pH revealed that the best fermentation performance of each strain, in terms of CO₂ production, was in the pH range of its original environment. Only one strain, mostly present in grape marc, produced a high biofilm level. Therefore, biofilm production does not seem to favor strain adaptation to grape marc condition.

PRACTICAL APPLICATION

These results demonstrate that grape juice and marc represent two different environments able to influence yeast strains distribution. The pH level can be included among the selection factors acting on yeast strains distribution. Grape marc can be considered a yeasts reservoir and its fermentation can be used for the development and isolation of new strains, genetically and physiologically different from those present in the grape juice.

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

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.

Molecular and Technological Characterization of Saccharomyces cerevisiae Strains Isolated from Natural Fermentation of Susumaniello Grape Must in Apulia, Southern Italy

The characterization of autochthonous Saccharomyces cerevisiae strains is an important step towards the conservation and employment of microbial biodiversity. The utilization of selected autochthonous yeast strains would be a powerful tool to enhance the organoleptic and sensory properties of typical regional wines. In fact, indigenous yeasts are better tailored to a particular must and because of this they are able to praise the peculiarities of the derived wine. The present study described the biodiversity of indigenous S. cerevisiae strains isolated from natural must fermentations of an ancient and recently rediscovered Apulian grape cultivar, denoted as "Susumaniello." The yeast strains denoted by the best oenological and technological features were identified and their fermentative performances were tested by either laboratory assay. Five yeast strains showed that they could be excellent candidates for the production of industrial starter cultures, since they dominated the fermentation process and produced wines characterized by peculiar oenological and organoleptic features.

Biodiversity and safety aspects of yeast strains characterized from vineyards and spontaneous fermentations in the Apulia Region, Italy

This work is the first large-scale study on vineyard-associated yeast strains from Apulia (Southern Italy). Yeasts were identified by Internal Transcribed Spacer (ITS) ribotyping and bioinformatic analysis. The polymorphism of interdelta elements was used to differentiate Saccharomyces cerevisiae strains. Twenty different species belonging to 9 genera were identified. Predominant on the grape surface were Metschnikowia pulcherrima, Hanseniaspora uvarum and Aureobasidium pullulans, whereas M. pulcherrima and H. uvarum were dominant in the early fermentation stage. A total of 692 S. cerevisiae isolates were identified and a number of S. cerevisiae strains, ranging from 26 to 55, was detected in each of the eight fermentations. The strains were tested for biogenic amines (BAs) production, either in synthetic media or grape must. Two Pichia manshurica, an Issatchenkia terricola and a M. pulcherrima strains were able to produce histamine and cadaverine, during must fermentation. The production of BAs in wine must was different than that observed in the synthetic medium. This feature indicate the importance of an "in grape must" assessment of BAs producing yeast. Overall, our results suggest the importance of microbiological control during wine-making to reduce the potential health risk for consumer represented by these spoilage yeasts.

Microbiological and physicochemical characterisation of caxiri, an alcoholic beverage produced by the indigenous Juruna people of Brazil

Caxiri is a traditional fermented alcoholic beverage produced from cassava and sweet potatoes by the indigenous Juruna or Yudjá people in Brazil. Our results showed that caxiri fermentation is invariably associated with the following: (i) an increase in the total microbial population, with yeast being the largest group detected; (ii) a decrease in reducing sugars, malic, tartaric, succinic, oxalic and propionic acid; and (iii) a final product characterised by a high content of ethanol and a high concentration of lactic acid. The microbial community dynamics were investigated by culture-based and culture-independent approaches. Fermentation was assisted by a complex microbial community that changed in structure and composition during the fermentative process. The bacterial population ranged from 3.05 to 5.33 log/mL, and the yeast population varied from 3.27 log CFU/mL to 7.34 log CFU/mL, showing that yeasts dominated the fermentation process after 48 h. A total of 343 colonies of bacteria and 205 colonies of yeasts were isolated and initially grouped by Amplified Ribosomal DNA Restriction Analysis (ARDRA) and by biochemical features. Phylogenetic analysis of the 16S rRNA gene sequences of representative isolates showed that the bacteria were mainly represented by endospore-forming low-G+C content Gram-positive bacilli (Bacillus spp.; 61.5% of the isolates), with Bacillus pumilus, Bacillus spp. (Bacillus cereus group), and Bacillus subtilis being the main species identified. The species Sphingomonas sp. and Pediococcus acidilactici were also found. The dominant yeast identified was Saccharomyces cerevisiae. Rhodotorula mucilaginosa, Pichia membranifaciens, Pichia guilliermondii and Cryptococcus luteolus were also found. According to the Polymerase Chain Reaction and Denaturing Gradient Gel Electrophoresis (PCR-DGGE) analysis, the microbial communities present during fermentation were probably from the raw materials, ambient or present on the utensils used during beverage preparation. The results indicated the necessity to combine both culture-dependent and culture-independent methods for a better description of the microbial communities in indigenous starch fermentations. Also, pH values decreased from 4.76 to 3.15 during fermentation. The ethanol concentration was 83.9 g/L and lactic acid reached 27.89 g/L by the end of the fermentation process.

Monitoring a mixed starter of Hanseniaspora vineae-Saccharomyces cerevisiae in natural must: impact on 2-phenylethyl acetate production

The effect of simultaneous or sequential inoculation of Hanseniaspora vineae CECT 1471 and Saccharomyces cerevisiae T73 in non-sterile must on 2-phenylethyl acetate production has been examined. In both treatments tested, no significant differences in Saccharomyces yeast growth were found, whereas non-Saccharomyces yeast growth was significantly different during all days of fermentation. Independently of the type of inoculation, S. cerevisiae was the predominant species from day 3 till the end of the fermentation. The dynamics of indigenous and inoculated yeast populations showed H. vineae to be the predominant non-Saccharomyces species at the beginning of fermentation in sequentially inoculated wines, whereas the simultaneous inoculation of S. cerevisiae did not permit any non-Saccharomyces species to become predominant. Differences found in non-Saccharomyces yeast growth in both fermentations influenced the analytical profiles of final wines and specifically 2-phenylethyl acetate concentration which was two-fold increased in sequentially inoculated wines in comparison to those co-inoculated. In conclusion we have shown that H. vineae inoculated as part of a sequential mixed starter is able to compete with native yeasts present in non-sterile must and modify the wine aroma profile.

Autochthonous fermentation starters for the industrial production of Negroamaro wines

The aim of the present study was to establish a new procedure for the oenological selection of Saccharomyces cerevisiae strains isolated from natural must fermentations of an important Italian grape cultivar, denoted as "Negroamaro". For this purpose, 108 S. cerevisiae strains were selected as they did not produce H(2)S and then assayed by microfermentation tests. The adopted procedure made it possible to identify 10 strains that were low producers of acetic acid and hydrogen sulphide and showed that they completed sugar consumption during fermentation. These strains were characterized for their specific oenological and technological properties and, two of them, strains 6993 and 6920, are good candidates as industrial starter cultures. A novel protocol was set up for their biomass production and they were employed for industrial-scale fermentation in two industrial cellars. The two strains successfully dominated the fermentation process and contributed to increasing the wines' organoleptic quality. The proposed procedure could be very effective for selecting "company-specific" yeast strains, ideal for the production of typical regional wines. "Winery" starter cultures could be produced on request in a small plant just before or during the vintage season and distributed as a fresh liquid concentrate culture.

Production of volatile metabolites by grape-associated microorganisms

Plant-associated microorganisms fulfill important functions for their hosts. Whereas promotion of plant growth and health is well-studied, little is known about the impact of microorganisms on plant or fruit flavor. To analyze the production of volatiles of grape-associated microorganisms, samples of grapes of the red cultivar 'Blaufraenkisch' were taken during harvest time from four different vineyards in Burgenland (Austria). The production of volatiles was analyzed for the total culturable microbial communities (bacteria, yeasts, fungi) found on and in the grapes as well as for single isolates. The microbial communities produced clearly distinct aroma profiles for each vineyard and phylogenetic group. Furthermore, half of the grape-associated microorganisms produced a broad spectrum of volatile organic compounds. Exemplary, the spectrum was analyzed more in detail for three single isolates of Paenibacillus sp., Sporobolomyces roseus , and Aureobasidium pullulans . Well-known and typical flavor components of red wine were detected as being produced by microbes, for example, 2-methylbutanoic acid, 3-methyl-1-butanol, and ethyl octanoate.

Profile of volatile compounds during papaya juice fermentation by a mixed culture of Saccharomyces cerevisiae and Williopsis saturnus

This study investigated the formation and utilization of volatile compounds during papaya juice fermentation by a mixed culture of Saccharomyces cerevisiae and Williopsis saturnus. Time-course papaya juice fermentations were carried out using pure cultures of S. cerevisiae var. bayanus R2 and W. saturnus var. mrakii NCYC2251 and a mixed culture of the two yeasts at a ratio of 1:1000 (R2:NCYC2251). Changes in S. cerevisiae cell population, Brix, sugar consumption and pH were similar in the mixed culture and in the S. cerevisiae monoculture. There was an early growth arrest of W. saturnus in the mixed culture fermentation. A range of volatile compounds were produced during fermentation including fatty acids, alcohols, aldehydes and esters and some volatile compounds including those initially present in the juice were utilized. The mixed culture fermentation of S. cerevisiae and W. saturnus benefited from the presence of both yeasts, with more esters being produced than the S. cerevisiae monoculture and more alcohols being formed than the W. saturnus monoculture. The study suggests that papaya juice fermentation with a mixed culture of S. cerevisiae and W. saturnus may be able to result in the formation of more complex aroma compounds and higher ethanol level than those using single yeasts.

Influence of indigenous yeasts on the fermentation and volatile profile of plum brandies

The aim of this study was to determine the influence of different yeasts isolated from fresh blue plum fruits (Aureobasidium sp.) and spontaneously fermenting plum musts (Kloeckera apiculata and Saccharomyces cerevisiae), as well as commercial wine and distillery strains, on the fermentation and chemical composition of plum brandies. Gas chromatography methods were used to detect major volatile components. The most rapid fermentation occurred in musts inoculated with S. cerevisiae. However, the highest concentration of ethanol was detected in samples after spontaneous fermentation (8.40% v/v). Plum brandies obtained after distillation contained from 66.3 (K. apiculata) up to 74.3% v/v ethanol (spontaneous fermentation). The samples after spontaneous fermentation were distinguished by a high content of acetoin, ethyl acetate and total esters, accompanied by a low level of methanol and fusel alcohols. Non-Saccharomyces yeasts were responsible for higher concentrations of esters and methanol, while S. cerevisiae strains resulted in increased levels of higher alcohols. It was also found that isolated indigenous strains of S. cerevisiae synthesized relatively low amounts of higher alcohols compared to commercial cultures. Samples obtained using the distillery strain of S. cerevisiae received the highest score (18.2) during sensory analysis and were characterized by a well-harmonised taste and aroma.

Optimizing the selection process of yeast starter cultures by preselecting strains dominating spontaneous fermentations

We propose an efficient and time-saving strategy for starter culture selection. Our approach is based on the accomplishment of 3 phases: (i) the selection of yeast strains dominating spontaneous fermentations, (ii) the selection among the dominant strains of those showing the best technological characteristics, and (iii) the final selection among good technological strains of those showing the desired qualitative traits. We applied this approach to wine fermentations, even though the same strategy has the potential to be employed for the selection of any type of starter culture. We isolated and identified yeast strains at the mid- and final stages of 6 spontaneous fermentations carried out in 3 different Spanish wineries. We identified all strains as Saccharomyces cerevisiae by restriction fragment length polymorphism of the ribosomal DNA internal transcribed spacer region, and subsequently distinguished each strain by analyzing the polymorphism of the inter-delta regions. Strains that were detected both at the mid- and final stages of the fermentation were considered dominant. Four dominant strains were finally selected and tested in pilot-scale fermentation, and their performance was compared with that of a commercial wine strain. All dominant strains showed good fitness and resulted suitable to be employed as starter cultures. One of the dominant strains isolated in this study is currently commercialized.

Yeast biodiversity in Slovenian wine regions: Case amino acids in spontaneous and induced fermentations of Malvasia

Microbial biodiversity can also be reflected in final product composition. The work described in this paper investigates the differences in the amino acid composition of 14 Malvasia musts/wines fermented with local and commercial starter yeasts, comparing all to the spontaneous fermentations of must of the same origin. We tried to ascertain whether the changes were dependent upon different initiations of fermentations. A comparative study of free and total amino acid evolution was prepared. The total concentration of 15 amino acids studied was 1975 mg/l, and the concentration of fraee amino acids was 1061 mg/l. Spontaneous and induced fermentations showed different fermentation rates. Three to nine days were needed to reduce sugar by 50%. Although the proline is regarded as non-assailable amino acid, decreases in concentration were observed. Lysine was the only amino acid where the concentration increased. The minimal uptakes of amino acids occurred during spontaneous fermentations, whereas the maximal uptakes were observed in the fermentations inoculated with local starters.

Wine yeasts for the future

International competition within the wine market, consumer demands for newer styles of wines and increasing concerns about the environmental sustainability of wine production are providing new challenges for innovation in wine fermentation. Within the total production chain, the alcoholic fermentation of grape juice by yeasts is a key process where winemakers can creatively engineer wine character and value through better yeast management and, thereby, strategically tailor wines to a changing market. This review considers the importance of yeast ecology and yeast metabolic reactions in determining wine quality, and then discusses new directions for exploiting yeasts in wine fermentation. It covers criteria for selecting and developing new commercial strains, the possibilities of using yeasts other than those in the genus of Saccharomyces, the prospects for mixed culture fermentations and explores the possibilities for high cell density, continuous fermentations.

Sour rot-damaged grapes are sources of wine spoilage yeasts

Yeast species of sound and sour rot-damaged grapes were analysed during fermentation and grape ripening in the vineyard, using general and selective culture media. During 2003 and 2004 vintages, microvinifications were carried out with sound grapes to which different amounts of grapes with sour rot were added. The wine spoilage species Zygosaccharomyces bailii was only recovered during fermentations with sour rot, reaching 5.00 log CFU mL(-1) (2003) and 2.48 log CFU mL(-1) (2004) at the end of fermentation. The study of yeast populations during the sour rot ripening process (2005 vintage) showed that the veraison-damaged grapes always exhibited higher total yeast counts and a much greater diversity of species. From a total of 22 ascomycetous species, 17 were present only in damaged grapes. The most frequent species were Issatchenkia occidentalis and Zygoascus hellenicus. The spoilage species Z. bailii and Zygosaccharomyces bisporus were consistently isolated exclusively from damaged grapes. This work demonstrates that one of the most dangerous wine spoilage species, Z. bailii, is strongly associated with sour rot grapes and survives during fermentation with Saccharomyces cerevisiae. The use of selective media provides a more accurate characterization of grape contamination species.

Yeast community structures and dynamics in healthy and Botrytis-affected grape must fermentations

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.

Kinetics and metabolic behavior of a composite culture of Kloeckera apiculata and Saccharomyces cerevisiae wine related strains

The kinetics and metabolic behavior of Kloeckera apiculata mc1 and Saccharomyces cerevisiae mc2 in composite culture was investigated. K. apiculata showed a higher viability through the fermentation; however the maximum cell density of both yeasts decreased. This behavior was not due to ethanol concentration, killer toxins production or competition for assimilable nitrogenous compounds between both yeasts. Despite the consistent production of secondary products by single culture of K. apiculata, an increase of these compounds was not observed in mixed culture. These results contribute to a better understanding of the behavior of non-Saccharomyces yeasts and their potential application in the wine industry.

Evolution of the population of Saccharomyces cerevisiae from grape to wine in a spontaneous fermentation

To determine the grape or winery origin of the Saccharomyces cerevisiae involved in spontaneous fermentation, musts were collected at different stages of wine-making process and fermented. First, grapes were collected in two different vineyards and crushed at the laboratory. Second, musts were collected after crushing and clarification in the cellar. Third, musts collected in the cellar were sterilized and inoculated with tartar deposit collected in the vats. The fourth fermentation was in the cellar. For the two vineyards, two hundred of S. cerevisiae clones were isolated for each of the four fermentations, driving to a library of 1600 clones. All the library was analysed by inter-delta PCR with a basic set of primers and about 20% of the library was further analysed by inter-delta PCR with an improved set of primers. Six, and more than 30 different PCR patterns were obtained from basic- and improved-PCR analysis, respectively. The amounts of each family were analysed at the different stages of wine making. Our study demonstrates that the two vineyards present different S. cerevisiae populations. Moreover the S. cerevisiae strains involved in spontaneous fermentation in the cellar originate partly from the vineyard and partly from the winery, in amounts varying with the must.

Isolation of epiphytic yeasts with potential for biocontrol of Aspergillus carbonarius and A. niger on grape

Antagonistic yeasts were isolated from the epiphytic flora associated with grape berries cv. Negroamaro and identified at species level using molecular methods. A total of 144 yeast isolates were tested in a preliminary screening on agar to select isolates showing a killer activity against Aspergillus carbonarius and A. niger, the main species responsible for the accumulation of ochratoxin A in grape. Twenty-eight yeast isolates were selected for their inhibitory effects on the above fungal species and assayed by an in vitro nutritional competition test for their antagonistic capacity towards three selected ochratoxigenic strains. Six yeast isolates belonging to five species, namely 2 isolates of Issatchenkia orientalis and one each of Metschnikowia pulcherrima, Kluyveromyces thermotolerans, Issatchenkia terricola and Candida incommunis, were finally selected and screened on wounded grape berries for their ability to inhibit infection by ochratoxigenic moulds. With the exception of the K. thermotolerans isolate, when inoculated at 10(9) CFU/wound, the other five challenger yeasts reduced the A. carbonarius and A. niger colonization on grape berry (P<0.05). In particular, the best antagonistic activity was shown by the two I. orientalis isolates. Results suggest that antagonist yeasts with the potential to control A. carbonarius and A. niger on grape can be found among the microflora associated with the berries.

Evidence for viable but nonculturable yeasts in botrytis-affected wine

AIMS

In Botrytis-affected wine, high concentrations of SO2 are added to stop the alcoholic fermentation and to stabilize the wine. During maturing in barrels or bottle-ageing, an unwanted refermentation can sometimes occur. However, results of the usual plate count of wine samples at the beginning of maturing suggest wine microbial stability. The aim of this study was to investigate the mode of yeasts survival after the addition of SO2 and to identify surviving yeasts.

METHODS AND RESULTS

Using direct epifluorescence technique, we observed the behaviour of cells after SO2 addition and compared the cell number determined by this method with the result of plate counts. The persistent yeast species were identified using two methods: polymerase chain reaction (PCR)-restriction fragment length polymorphism and PCR-denaturing gradient gel electrophoresis. They were identified as Saccharomyces cerevisiae and Candida stellata, and after few months of maturing, other spoiling yeasts appeared, like Rhodotorula mucilaginosa or Zygosaccharomyces bailii.

CONCLUSIONS

All characteristics of the cells lead to the conclusion that yeast persisted in wine in a viable but nonculturable-like state (VBNC). Suppression of the effect of free-SO2 did not lead to the resuscitation of the cells; however, another method proved the capacity of the cells to exit from the VBNC-like state.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study permits the characterization of the presence of VBNC-like yeasts in wine. The 'refermentation' phenomenon is probably due to the exit of the VBNC state.

Predominance of Saccharomyces uvarum during spontaneous alcoholic fermentation, for three consecutive years, in an Alsatian winery

AIMS

The purpose of this study was to determine the origin of the yeasts involved in the spontaneous alcoholic fermentation of an Alsatian wine.

METHODS AND RESULTS

During three successive years, must was collected at different stages of the winemaking process and fermented in the laboratory or in the cellar. Saccharomyces yeasts were sampled at the beginning and at the end of the fermentations. Saccharomyces cerevisiae clones were genetically characterized by inter-delta PCR. Non-S. cerevisiae clones were identified as Saccharomyces uvarum by PCR-RFLP on MET2 gene and characterized at the strain level by karyotyping. The composition of the Saccharomyces population in the vineyard, after crushing and in the vat was analyzed. This led to three main results. First, the vineyard Saccharomyces population was rather homogeneous. Second, new non-resident strains had appeared in the must during the winemaking process. Finally, the yeast population in the vat only consisted in S. uvarum strains.

CONCLUSION

This 3-year study has enabled us to show the involvement of indigenous S. uvarum in the alcoholic fermentation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study gives a first insight into the polymorphism of S. uvarum strains involved in a spontaneous alcoholic fermentation.

Dynamics of indigenous yeast populations during spontaneous fermentation of wines from Mendoza, Argentina

Fermentation of wine is a complex microbial reaction, which involves the sequential development of various species of yeasts and lactic acid bacteria. Of these, yeasts are the main group responsible for alcoholic fermentation. The aim of this work was to study, under industrial conditions, the evolution of yeast populations and to describe the individual evolution of the most important yeasts during three spontaneous fermentations of Malbec musts from Argentina. This work shows the significant participation of non-Saccharomyces yeasts during spontaneous fermentation of musts, with the ubiquitous presence of three main species: Kloeckera apiculata, Candida stellata and Metschnikowia pulcherrima.

Effect of wine yeast monoculture practice on the biodiversity of non-Saccharomyces yeasts

AIMS

The objective of this work was to study the effect of the use of Saccharomyces cerevisiae monocultures over the biodiversity of non-Saccharomyces yeasts in wine-producing areas in Chile.

METHODS AND RESULTS

Microvinifications were carried out with grape musts of two areas. In one of them, the fermentation is carried out mainly in a spontaneous manner, whereas in the other the musts are inoculated with commercial yeasts. The isolated yeasts were identified by the internal transcribed (ITS)/restriction fragment length polymorphism technique. In the industrial production area less variability of yeast genera was observed as compared with the traditional area, an observation that is greatest at the end of the fermentation. Furthermore, a study of the production of extracellular enzymes was done. The majority of the yeasts showed at least one of the activities assayed with the exception of beta-glycosidase.

CONCLUSION

The results suggest that in the industrialized area the diversity of yeasts is less in the traditional area. Likewise, the potentiality of the non-Saccharomyces yeasts as enzyme producers with industrial interest has been confirmed.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows the negative effect of the use of monocultures over the biodiversity of yeasts in wine-producing regions.

Molecular identification and genetic diversity within species of the genera Hanseniaspora and Kloeckera

Three molecular methods, RAPD-PCR analysis, electrophoretic karyotyping and RFLP of the PCR-amplified ITS regions (ITS1, ITS2 and the intervening 5.8S rDNA), were studied for accurate identification of Hanseniaspora and Kloeckera species as well as for determining inter- and intraspecific relationships of 74 strains isolated from different sources and/or geographically distinct regions. Of these three methods, PCR-RFLP analysis of ITS regions with restriction enzymes DdeI and HinfI is proposed as a rapid identification method to discriminate unambiguously between all six Hanseniaspora species and the single non-ascospore-forming apiculate yeast species Kloeckera lindneri. Electrophoretic karyotyping produced chromosomal profiles by which the seven species could be divided into four groups sharing similar karyotypes. Although most of the 60 strains examined exhibited a common species-specific pattern, a different degree of chromosomal-length polymorphism and a variable number of chromosomal DNA fragments were observed within species. Cluster analysis of the combined RAPD-PCR fingerprints obtained with one 10-mer primer, two microsatellite primers and one minisatellite primer generated clusters which with a few exceptions are in agreement with the groups as earlier recognized in DNA-DNA homology studies.