INTRODUCTION. Milano, Italy. Italy

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1 Microbiology (2015), 161, DOI /mic The vintage effect overcomes the terroir effect: a three year survey on the wine yeast biodiversity in Franciacorta and Oltrepò Pavese, two northern Italian vine-growing areas Ileana Vigentini, 1 3 Gabriella De Lorenzis, 2 3 Vincenzo Fabrizio, 1 Federica Valdetara, 1 Monica Faccincani, 3 Carlo Alberto Panont, 4 Claudia Picozzi, 1 Serena Imazio, 5 Osvaldo Failla 2 and Roberto Foschino 1 Correspondence Roberto Foschino roberto.foschino@unimi.it 1 Department of Food, Environmental and Nutrition Sciences, Università degli Studi di Milano, Milano, Italy 2 Department of Agricultural and Environmental Sciences, Università degli Studi di Milano, Milano, Italy 3 Consorzio per la Tutela del Franciacorta, Erbusco, Brescia, Italy 4 ex Consorzio Tutela Vini Oltrepò Pavese, Torrazza Coste, Pavia, Italy 5 Department of Life Sciences, Università degli Studi di Modena e Reggio Emilia, Italy Received 27 September 2014 Accepted 10 November 2014 A three year survey on the dominant yeast populations in samples of air, must and wine in different vineyards and cellars of two northern Italian vine-growing territories (six sites in Franciacorta and eight sites in Oltrepò Pavese areas) was carried out. A total of 505 isolates were ascribed to 31 different species by RFLP analysis of the ITS1 5.8SrRNA ITS2 region and partial sequence analysis of the 26S rrna gene. The most commonly found species were Saccharomyces cerevisiae (frequency, F %; incidence, I %), Hanseniaspora uvarum (F %; I955.3 %), Metschnikowia fructicola (F %; I 55.0 %) and Torulaspora delbrueckii (F %; I 53.8 %). Among 270 S. cerevisiae new isolates, 156 (57.8 %) revealed a different genetic pattern through polymorphism analysis of the interdelta regions by capillary electrophoresis, while 47 isolates (17.4 %) were clones of starter cultures. By considering the Shannon Wiener index and results of principal component analysis (PCA) analyses, the year of isolation (vintage) proved to be a factor that significantly affected the biodiversity of the yeast species, whereas the geographical site (terroir) was not. Seventy-five per cent of S. cerevisiae isolates gathered in a unique cluster at a similarity level of 82 %, while the remaining 25 % were separated into minor groups without any evident relationship between d-pcr profile and territory, year or source of isolation. However, in six cases a similar strain appeared at the harvesting time both in Franciacorta and Oltrepò Pavese areas, whereas surprisingly no strain was reisolated in the same vineyard or cellar for consecutive years. INTRODUCTION In winemaking, yeasts are essential for the transformation of grape sugars into ethanol and carbon dioxide through alcoholic fermentation; nonetheless, due to their specific 3These authors contributed equally to this paper. Abbreviations: ADY, active dry yeast; CE, capillary electrophoresis; ITS, internal transcribed spacer; LSD, least significant difference; PCA, principal component analysis; UPGMA, unweighted pair group method with arithmetic means. Two supplementary figures are available with the online Supplementary Material. enzymic activities and cell autolysis, they can also generate typical sensorial characteristics in wine, like secondary flavours and smoothness (Romano et al., 2003a). Although selected Saccharomyces strains are usually added by oenologists as starter cultures to control the fermentative process, several micro-organisms enter the must from the vineyard environment, winery facilities and cellar equipment, and these can affect the quality of the end product. Nowadays, for a certain style of wines, the use of the so called autochthonous yeasts is considered essential in providing for the valorization and preservation of the environmental microbial biodiversity (Pretorius, 2000). In G 2015 The Authors Printed in Great Britain

2 Autochthonous yeasts may not exist in wine environments fact, it has been suggested that the land from which the grapes are grown imparts a unique quality to the wine, especially when spontaneous fermentations are carried out (Csoma et al., 2010; Di Maio et al., 2012). According to an OIV resolution (International Organization of Vine and Wine, 2010), terroir refers to an area in which collective knowledge of the interactions between the identifiable physical and biological environments and applied viticultural and oenological practices develops, giving distinctive characteristics for the products originating from this area. This assumption is at the base of the Appellation of Origin systems around the globe, with a strong impact on the wine market since they drive consumer choices. Many research groups have explored the opportunity to isolate, select and use indigenous strains with technological properties and quality traits as a strategic asset for wine-makers to unequivocally link a wine with its environment of production (Furdíkova et al., 2014; Martínez et al., 2004; Rodríguez- Palero et al., 2013; Settanni et al., 2012; Tosi et al., 2009; Tristezza et al., 2012). This experimental activity might also be interesting for the manufacturers of starter cultures, because it is the basis for genetic improvement and formulation of new products (Giudici et al., 2005; Mannazzu et al., 2002). However, the isolation of new strains with novel oenological properties is infrequent because different populations of yeasts naturally succeed each other during the must transformation (Torija et al., 2001; Vigentini et al., 2014) and they contribute in an unpredictable manner. Moreover, contamination with commercial starter cultures is possible and uncontrollable, since they are used for a long time and spread throughout the territory (Blanco et al., 2011; Cordero-Bueso et al., 2011a). Sometimes the phenomenon of codominance between autochthonous and commercial strains has been observed in spontaneous and controlled fermentations, with huge variation in the frequency of appearance of different yeast population (Beltran et al., 2002; Santamaria et al., 2008; Valero et al., 2005). The available commercial strains are numerous, and the same yeast is often called by different names or acronyms, depending on the manufacturers of the starter culture (Fernández-Espinar et al., 2001; Vigentini et al., 2009). An obvious consequence of this practice is the standardization of sensory characters resulting from the fermentation process, including in quality wines, at the expense of the originality of aromas that could be expressed from the same products by exploiting indigenous micro-organisms (Pretorius, 2000; Romano et al., 2003b). All of these considerations demonstrate that the debate on autochthonous yeasts is still open and, in any case, the development of analytical protocols for the accurate identification of strains is a requisite to demonstrating a possible link between wine and territory. The present work assesses the microbial diversity in oenological environments (vineyard air, must and base wine), in terms of yeast species and Saccharomyces sensu stricto group strains, through use of a large-scale sampling plan over a period of three consecutive years in fourteen different vineyards and respective cellars, located in two Lombard vine-growing areas (Franciacorta and Oltrepò Pavese). These territories are traditionally suited for the production of sparkling wines by the Champenoise method with the respective Italian designation of origin Franciacorta D.O.C.G and Oltrepò Pavese Metodo Classico D.O.C.G. METHODS Sampling and yeast isolation. Yeast isolates were collected during the 2009, 2010 and 2011 vintages in the Franciacorta (Brescia, Italy) and Oltrepò Pavese (Pavia, Italy) areas, which are more than 100 km apart and separated by the Po river. Each year, sampling was performed during July (air), August (must) and October (base wine) at the same places. Six vineyards (named A, B, C, D, E and F, with a maximum distance between them of 14 km) prevalently planted with Chardonnay cultivar and their related cellars in Franciacorta area, and eight vineyards (G, H, I, J, K, L, M and N, with a maximum distance among them of 18 km) prevalently planted with Pinot noir cultivar and their related cellars in Oltrepò Pavese area were involved (Fig. 1). In both territories, controlled fermentations were generally performed for the base wine production of sparkling wine by the Champenoise method through the inoculation of active dry yeast (ADY) cultures. Air sampling was carried out in July when the ripening of berries of both cultivars was advanced. In each vineyard, a 1 m 3 volume of air (two aliquots of 500 l in different points of the vineyard) was collected by an air sampler MAS 100 Eco (VWR International PBI) equipped with a support for Petri dishes. The instrument was manually transported between rows in the fields keeping it at a distance of approximately 30 cm from the plants and m from the ground (at the height of the bunches). Yeast counts and isolation were carried out using YPD medium (10 g yeast extract l 21,20g peptone l 21, 20 g glucose l 21 ) combined with 18 g agar l 21, 200 mg K 2 S 2 O 5 l 21, 100 mg chloramphenicol l 21 and adjusted to ph 3.6 with tartaric acid. The plates were incubated at 25 uc in anaerobic conditions (GasPak system, Mikrobiologie Anaerocult A, Merck) for 5 days. Must sampling was carried out in August, at the wineries that were processing the grapes of the vineyards at which the air had previously been analysed; fresh juices were collected just after crushing, before treatment with sulphur dioxide. Finally, base wine sampling was performed in October, directly from the tanks when alcoholic fermentation of the relevant must was completed. Two 100 ml aliquots of must or wine sample for each winery were transferred to laboratories, storing them at 4 uc. Count and isolation of yeasts were carried out by culture techniques according to Vigentini et al. (2014). In addition, forty samples of commercial starter cultures (ADY) sold in Lombardy by six different brands were analysed in order to isolate and recognize whether starter strains were present in the collection of new isolates (Table 1). The choice of products was made after interviewing the involved winemakers. Yeast isolates were maintained at 280 uc in YPD broth with 20 % (v/v) glycerol. Yeast identification and biodiversity evaluation. The protocol for yeast DNA extraction was described by Vigentini et al. (2012). DNA samples were stored at 220 uc. A preliminary species identification of the isolates was carried out using RFLP analysis of the ribosomal internal transcribed spacer (ITS) 1 5.8S rrna gene region ITS 2 (ITS region) according to Esteve-Zarzoso et al. (1999). A T Gradient Biometra Thermocycler (Biometra) was used for DNA amplification. Approximately 2 mg of each PCR product was digested with Hin6I restriction endonuclease (Fermentas) according to the 363

3 I. Vigentini and others Pavia Po River L N I F C A B Iseo Lake E D K J M G H Brescia Fig. 1. Site sampling of the 14 vineyards and related wineries, indicated by the letters A N, examined in 2009, 2010 and 2011 vintages located in the Franciacorta and Oltrepò Pavese areas. Bar, 100 km. supplier s instructions. The restriction fragments were separated and assessed by gel electrophoresis on 1.5 % agarose gels with TAE buffer (0.4M Tris/acetate, 0.01 M Na 2 EDTA, ph 8). Isolates showing the same restriction profile were grouped together and some samples per cluster were used for amplification and partial sequencing of the ITS region, as described above, or of the 26S rdna D1/D2 domain, using primers NL1 and NL4 (Spírek et al., 2003). Amplification products were sequenced by an outside provider (Primm, Milan, Italy). The sequences obtained were identified through the BLAST algorithm by comparison with sequences listed in databases ( A further analysis was performed for all yeast isolates attributed to Saccharomyces sensu stricto group to discriminate within oenological species, such as Saccharomyces bayanus, Saccharomyces cerevisiae and Saccharomyces pastorianus. A PCR protocol based on species-specific primers targeting the HO (homothallism) gene was used according to the protocol of de Melo Pereira et al. (2010). A measurement of the general diversity found in yeast communities was determined by calculating the richness of species (S ) and the Shannon Wiener index (H ) (Cordero Bueso et al., 2011a). Moreover, the frequency (F9) and the incidence (I ) were calculated according to Tristezza et al. (2013). ANOVA and Fisher s least significant difference (LSD) test were performed to assess the main effects of the investigated factors (Cordero Bueso et al., 2011a) using StatGraphics Centurion XVI statistical package. S. cerevisiae interdelta regions typing by capillary electrophoresis detection. The new isolates and those isolated from commercial starter cultures, which were attributed to S. cerevisiae strains, were subjected to typing by the amplification of interdelta (d- PCR) regions. Amplification was performed according to the protocol described by Legras & Karst (2003). The delta21 primer was 59-dyelabelled with 6-carboxyfluorescein (6-FAM; Primm) in order to detect amplification of the product in capillary electrophoresis (CE) (Tristezza et al., 2009). To determine the quality of d-pcr products, the amplification fragments were separated by electrophoresis in 2.0 % (w/v) agarose gels submitted to 100 V for 1.5 h in 16 TAE buffer and detected by ethidium bromide straining. The d-pcr products were then separated and detected by CE in an ABI Prism 310 Genetic Analyzer (Applied Biosystems Life Technologies) using POP-4 polymer, 310 Genetic Analyzer Buffer with EDTA, and a 47 cm650 mm capillary (Applied Biosystems). As reported by Vigentini et al. (2012), the samples were prepared in a solution of 0.9 ml ofd-pcr amplified fragments diluted 1 : 1000, 20 ml of formamide (Applied Biosystems) and 0.75 ml size standard GENESCAN-1200 LIZ (Applied Biosystems). The solution was incubated at 95 uc for 3 min in order to denature DNA fragments and cooled on ice for 5 min. The method used for CE was injection for 20 s at 1.5 kv and migration at 8 kv for 80 min with a run temperature of 60 uc. Data recording was performed using ABI Prism GeneMapper 3.7 software (Applied Biosystems) and fragments between 50 and 1200 bp were scored. Peaks showing a fluorescent intensity value less than 100 were not considered. The discrimination power of the CE protocol was estimated as follows: three independent DNA extractions of four different S. cerevisiae strains were performed and the genomic DNA was used as template in independent d-pcrs. The amplified fragments were then resolved in CE and d-pcr profiles were transformed in binary matrix (15presence, 05absence of amplified fragment) in order to display the similarity among replicates of each sample by cluster analysis. Based on the similarity matrix performed by GenAlEx 6.5 software (Peakall & Smouse 2006) using Dice s coefficient, a UPGMA (unweighted pair group method with arithmetic means) dendrogram was built using MEGA 5.0 software (Tamura et al. 2011). The lowest value of similarity that grouped the replicates of a same S. cerevisiae strain was used to determine the discrimination threshold among the yeast isolates. 364 Microbiology 161

4 365 Table 1. Distribution of the yeast species as number of isolates collected from air (a), must (m) and base wine (w) samples during the 2009, 2010 and 2011 vintages in two Lombard vine-growing areas Yeast species F I Franciacorta Oltrepò Pavese Franciacorta Oltrepò Pavese Franciacorta Oltrepò Pavese Aureobasidium pullulans 4 (a) 1 (a) 3.2 % 1.0 % Candida diversa 1 (m) 0.8 % 0.2 % Candida glabrata 1 (m) 0.8 % 0.2 % Candida parapsilosis 1 (m) 0.8 % 0.2 % Candida railenensis 14 (m), 4 (w) 1 (m) 9.5 % 3.8 % Candida zemplinina 1 (m) 1 (m) 1 (m) 3 (m) 4.8 % 1.2 % Cryptococcus flavescens 1 (m) 0.8 % 0.2 % Cryptococcus laurentii 4 (a) 1.6 % 0.8 % Hanseniaspora uvarum 1 (m) 13 (m), 2 (w) 4 (m), 2 (w) 1 (m) 5 (m) 14.3 % 5.5 % Hanseniaspora vinae 5 (m) 3.2 % 1.0 % Issatchenkia occidentalis 6 (m) 2 (m) 5 (m), 1 (w) 2 (m) 6.3 % 2.8 % Issatchenkia terricola 1 (a), 1 (m) 5 (m) 1 (a), 6 (m) 7.1 % 2.8 % Lachancea thermotolerans 2 (m) 1 (m) 2.4 % 0.6 % Meyerozyma guillermondii 1 (m) 0.8 % 0.2 % Metschnikowia fructicola 15 (m) 2 (m) 8 (m) 11.1 % 5.0 % Metschnikowia pulcherrima 3 (m) 1.6 % 0.6 % Pichia fermentans 1 (a), 5 (m), 3 (w) 6.3 % 1.8 % Pichia fluxuum 3 (w) 2 (m), 4 (w) 4.0 % 1.8 % Pichia kluyveri 10 (m) 1 (m) 4.0 % 2.2 % Pichia kudriavzevii 1 (w) 2 (m) 1.6 % 0.6 % Pichia manshurica 1 (w) 0.8 % 0.2 % Pichia membranefaciens 9 (w) 4 (w) 1 (m) 3 (w) 1 (m), 1 (w) 9.5 % 3.8 % Rhodotorula glutinis 4 (a) 3.2 % 0.8 % Rhodotorula graminis 2 (m) 0.8 % 0.4 % Rhodotorula nothofagi 1 (a) 0.8 % 0.2 % Saccharomyces cerevisiae 21 (m), 34 (w) 7 (a), 13 (m), 50 (w) 27 (m), 11 (w) 1 (a), 17 (m), 6 (w) 31 (m), 19 (w) 1 (a), 16 (m), 16 (w) 58.7 % 53.5 % Torulaspora delbrueckii 1 (w) 4 (m) 5 (m) 6 (m) 3 (m) 10.3 % 3.8 % Wickerhamomyces 3 (m) 1 (m) 2.4 % 0.8 % anomalus Zygoascus hellenicus 1 (m) 0.8 % 0.2 % Zygoascus bailii 10 (m), 1 (w) 2 (m), 1 (w) 1 (w) 2 (w) 1 (w) 8.7 % 3.6 % Zygoascus parabailii 1 (m), 1 (w) 1 (m) 2.4 % 0.6 % Autochthonous yeasts may not exist in wine environments

5 I. Vigentini and others Data analysis. To investigate a possible correlation between species diversity and abiotic factors such as year, area or material of isolation, a principal component analysis (PCA; Price et al. 2006) was performed by using GenAlEx 6.5 software. The dataset was created on the frequencies of the single species found in the air and must samples; the isolates collected from wine samples were excluded from the calculation, since S. cerevisiae species is normally added with ADY cultures to control fermentation. As regards the diversity within S. cerevisiae species, the d-pcr profile per each isolate obtained by CE was transformed in binary matrix. To display the genetic similarity among isolates and discriminate the strains, a cluster analysis was carried out, as already described above for the assessment of the discrimination power of the CE protocol. Moreover, the data obtained from the isolates that were not clones of commercial strains were subjected to PCA (Price et al., 2006) by GenAlEx 6.5 software (Peakall & Smouse, 2006), starting with the SSR correlation matrix. The SPSS 21.0 program (SPSS) was used to display a 2D representation of genetic relationship among genotypes. A structure analysis was performed using STRUCTURE software package (Pritchard et al., 2000). To estimate the K value (K number of ancestral genetic groups), the algorithm was run 10 times per each K value from 1 to 10, using the following parameters: burn-in steps (i.e. an initiation phase without result recording) and steps for data acquisition, assuming admixture. According to Evanno et al. (2005), the K value was chosen estimating the highest value of DK as the mean of the absolute values of L (K) averaged over 10 runs, divided by the SD of L(K), DK5m[L(K+1)22 L(K)+ L(K21)] s 21 [L(K)]. L(K) is an estimate of the posterior probability of the data for a given K; L (K) is the rate of change of the likelihood function with respect to K [L (K)5L(K)2L(K21)]; L (K) is the absolute value of the difference between successive values of L (K). Based on the percentage of membership assignment, each sample is probabilistically assigned to a population (membership values higher than 0.8), or jointly to two or more populations indicating admixture. RESULTS Evaluation of species biodiversity A total of 505 yeast isolates (278 from Franciacorta and 227 from Oltrepò Pavese areas) were ascribed to 31 different species (Table 1). In particular, 26 isolates found in the air samples were attributed to seven yeast species, 297 isolates collected from the must samples belonged to 26 species and 182 isolates retrieved in base wine samples were representative of 12 species. Since the RFLP analysis of the ITS region, and the partial sequencing of ITS region or 26S rdna gene, may be insufficient to discriminate among the oenological species of Saccharomyces sensu stricto group, an investigation on the HO gene by species-specific PCR-based assay was performed. Results revealed that all 270 Saccharomyces isolates could be ascribed to S. cerevisiae, as they generated a single amplicon of approximately 400 bp with ScHO set primers, while no amplification products were obtained with LgHO primer pairs (de Melo Pereira et al., 2010). In general, the yeast species most frequently isolated and with the highest incidence were S. cerevisiae (F %, I %), Hanseniaspora uvarum (F %, I 55.5 %), Metschnikowia fructicola (F %, I 55.0 %) and Torulaspora delbrueckii (F %, I 53.8 %) (Table 1), in accordance with recent literature (Barata et al., 2012; Zott et al., 2010). The air sampling was carried out in the same vineyards every year after the grape veraison, depending on the cultivar. Following our protocol, 27 samples did not reveal the presence of yeasts in 1 m 3, whereas 15 samples showed a log mean count value of 0.95±0.45 per m 3, with different isolation rates for some species, such as S. cerevisiae (F %, I %), Aureobasidium pullulans (F %, I %), Rhodotorula glutinis (F959.5 %, I %) and Cryptococcus laurentii (F954.8 %, I %). The climatic conditions, rainfall and phytosanitary treatments (Cordero-Bueso et al., 2011a; Milanović et al., 2013) probably affect the presence of fungi in the air, since clear differences were found throughout territories and vintages: in particular, S. cerevisiae was consistently isolated in the air of Oltrepò Pavese vineyards, while no yeast was collected in 2010 and 2011 in the Franciacorta area. The musts were sampled immediately after the drainage of the grape juice and before the addition of sulfur dioxide, in order to collect samples at the harvesting time from a large mass of raw materials, deriving from the vineyard where the air sampling was done. The log mean value of yeast counts was 6.25±0.66 per ml, with most isolates belonging to S. cerevisiae (F %, I %), H. uvarum (F %, I 58.1 %), Met. fructicola (F %, I 58.4 %), T. delbrueckii (F %, I 56.1 %) and Candida railenensis species (F %, I 55.1 %). The sampling of wines was performed at the end of the alcoholic fermentation from the tanks in which the relevant must, previously analysed, was processed. The log mean count was 3.75±0.93 per ml. The reason for this low value is because the samples were taken from the top of the tanks without mixing the vinous mass to meet the precautions intended by winemakers. As expected, S. cerevisiae was the predominant species (F %, I %); interestingly, the isolation of minor species like Pichia membranefaciens (F %, I 59.3 %), Pichia fluxuum (F959.5 %, I 53.8 %) and Zygosaccharomyces bailii (F959.5 %, I %) were shown to be detectable at an ethanol level.10.5 %, v/v, and total SO 2.40 mg l 21. The presence of some yeast species was discontinuous along the timeframe studied. Only S. cerevisiae was found during all three investigated years in both territories, whereas Candida zemplinina, H. uvarum, Issatchenkia occidentalis, P. membranefaciens, T. delbrueckii and Z. bailii were detected for at most two years. Excluding the species represented by one isolate, Cryptococcus laurentii, Hanseniaspora vinae, Pichia kudriavzevii and Rhodotorula graminis were recovered only in the Franciacorta area at different vintages, while Metschnikowia pulcherrima, Pichia fermentans and R. glutinis were detected only in the Oltrepò Pavese area, but all of these yeasts were not found in more than one year. Forty-eight isolates were obtained from ADY samples and all of them were ascribed to S. cerevisiae species. 366 Microbiology 161

6 % 2 3 Autochthonous yeasts may not exist in wine environments On the basis of the number of identified species deriving from air and must samples, the richness (S) and the Shannon Wiener indexes (H ) were calculated. The isolates collected from base wine samples and those recognized as commercial starter cultures (see next paragraph) were omitted from the calculation, because they would have introduced a bias in the biodiversity assessment. The richness index in the Franciacorta area was higher than that found in Oltrepò Pavese, since 25 vs 20 different yeast species were isolated, respectively. Although data from the Franciacorta territory showed a level of yeast biodiversity (H 52.38) greater than those from Oltrepò Pavese (H 52.08), ANOVA revealed that this difference was not significant (P50.62). Conversely, the vintage proved to be a factor that significantly affected the yeast biodiversity since the values of the Shannon Wiener index determined for each year were different (P,0.05); in particular, the H calculated in 2010 (H 52.38) was different from those of 2009 (H 51.26) and 2011 (H 51.54) vintages, by applying the LSD test (at 95 %). In order to uncover relationships between microbial diversity and vintage or terroir, data describing 30 species frequencies in different years, areas or materials of isolation were processed by PCA. The first three principal components explained over 66 % of the total variability (Fig. 2). In the scatter plot, a distribution of the samples according to the year of isolation was noticed. In particular, the data from the samples collected in 2009 were grouped in the negative quadrant of the first two coordinates, while those observed in 2010 proved to be the most dispersed ones, confirming the results previously pointed out by the Shannon Wiener index. On the contrary, a clear connection among frequencies of yeast species and vine-growing area or material of isolation was not found (data not shown). S. cerevisiae strain diversity by d-pcr typing A preliminary evaluation of the discriminating power of the d-pcr typing technique in our experimental conditions was carried out. The analysis of electrophoretic profiles allowed determination of a size range of 2 bp as a sensibility threshold of the molecular marker used. Three independent d-pcrs per four different S. cerevisiae strains were performed. In the UPGMA dendrogram obtained (Fig. S1, available with the online Supplementary Material), the replicates of each strain were grouped correctly in the same cluster; particularly, similarity values within the cluster ranged from 98.0 % to 100 %. Therefore, the lowest value of similarity grouping the replicates of the same yeast (98.0 %) was assumed to be the threshold limit of the protocol to separate strains. In other words, isolates having a similarity value higher than this limit were considered clones of the same strain. The new isolates (270) and those obtained from starter cultures (48), that were previously identified as S. cerevisiae, were analysed by the d-pcr typing protocol. For each sample, a clear and unambiguous amplification pattern was generated and separated by CE. A total of 220 polymorphic d-pcr products were scored among new and commercial S. Year % % Fig. 2. Scatter plot obtained from PCA applied to 299 yeast isolates collected from air and must samples during the 2009, 2010 and 2011 vintages in the Franciacorta and Oltrepò Pavese areas. The axes represent the first three principal components (PCs) and the variability explained by each PC is reported as a percentage of the total variability

7 I. Vigentini and others cerevisiae strains, in the range of bp. The number of fragments detected ranged from 17 to 42 for each isolate, with an average of 21. No monomorphic product was found, while a 460 bp fragment was revealed to be common to 280 isolates out of 318 (88.1 %). In Fig. 3 the UPGMA dendrogram obtained with the d-pcr profiles from all S. cerevisiae isolates is shown. In general, the range of genetic similarity based on the Dice s coefficient ranged between %. One-hundred and sixty-two isolates could be considered clones of some strains, since they showed similarity values higher than the determined discrimination limit (98.0 %); on the other hand, 156 amplification patterns were distinctive and were attributed to a single strain. A proportion accounting for 75 % of S. cerevisiae isolates, including 94 % of the starter cultures investigated, grouped in a large unique cluster at a similarity level of 82 %. The remaining 25 % of isolates were separated in minor groups, some of them represented by one strain. No specific clusters could be ascribed to the geographical origin or year of isolation, but samples were casually distributed without any evident relationship between d-pcr profile and territory, year or matrix of isolation. Out of 48 isolates from starter cultures, only 18 were recognized as distinct d-pcr patterns, indicating that the manufacturers of commercial ADY often replicate the same strains or those of their competitors, by changing the names. Furthermore, among the new isolates, 47 (17.4 %) revealed a d-pcr profile undistinguishable from starter yeasts (Table 2). The most common electrophoretic profile was shared by 23 isolates: seven from commercial cultures of different producers, six isolated during the 2009 vintage in Franciacorta, three during the 2009 vintage in Oltrepò Pavese, four during the 2010 vintage in Franciacorta and three during the 2011 vintage in Franciacorta. Frequently, isolates showing an identical d-pcr pattern were collected from samples isolated from the same or neighbouring vineyards/cellars. Nevertheless, an identical amplification profile was identified in the same vintage in Franciacorta and Oltrepò Pavese in six cases (Fig. 3): the isolates 780 (cellar B), 768 (D), 539 (E), 781 (J) and 783 (K) in 2009; the isolates 788 and 790 (C), 787 and 789 (cellar F), 793 and 522 (I), 791 and 510 (K), in 2009; the isolates 813 (B), 814 and 71 (H), 521 (J), 815 and 816 (L), and 823 (M) in 2009; the isolates 848 (C) and 849 (N) in 2009; the isolates 637 (F) and 639 (J) in 2010; and the isolates 667 (B), 668 (E), 669 (H) and 670 (G) in 2010 (Table 2). On the other hand, in only two cases an undistinguishable d-pcr pattern appeared in different years within the same vine-growing area (Franciacorta): these were the isolates 782 (B) and 705 (F) present in 2009 and 632 (E) found in 2010; and the isolates 637 (F) present in 2010 and 638 (A) found in Interestingly, some S. cerevisiae strains collected from the air (the isolates 618 at vineyard K in 2009, 686 at vineyard N in 2010 and 585 at vineyard I in 2011) were then found in must samples picked up at neighbouring cellars in the same vintage (the isolates 620 at cellar G in 2009; 687 and 689 at cellar K, 688 at cellar J in 2010; and 776 at cellar in 2011, respectively). In only one case the same strain was identified both in the air (829 and 830 at vineyard L in 2009) and in wine (828 at cellar I in 2009). Analysis of population structure The genetic structure of 223 S. cerevisiae isolates was analysed using STRUCTURE software. Multiple analyses were performed using a varying number of assumed populations (K51 10). A graphic representation of the most appropriate groups inferred in this dataset is reported in Fig. 4. The maximum resolution was achieved at K52. A proportion accounting for 81.6 % of samples showed an average estimated major membership proportion.0.8. Therefore, according to their largest ancestry membership fraction, the yeast strains could be classified as mainly belonging to one of two distinct genetic groups. The other 18.4 % was considered admixed. The ancestral groups 1 (G1) and 2 (G2) clustered 11.5 % and 88.5 %, respectively, of S. cerevisiae isolates showing a membership proportion higher than 0.8. In G1, samples collected during the 2011 vintage and from air were not grouped. Considering each variable, G1 clustered 3.20 % and % of total samples collected from must and wine, respectively, % and 2.70 % of yeasts isolated during the 2009 and 2010 vintage, respectively, and 7.30 % and % of isolates collected in Franciacorta and Oltrepò Pavese areas were also clustered. The composition of G2 was very dissimilar to G1, grouping the total samples collected during the 2011 vintage and from air, % and % of samples were collected from must and wine, respectively, % and % of yeasts were isolated during the 2009 and 2010 vintage, respectively, and % and 84.8 % of isolates were collected in Franciacorta and Oltrepò Pavese. As observed for the PCA data (Fig. S2), the structure analysis discriminated the samples into two groups (a major and a minor group), where the first two coordinates, accounting for about 50 % of total variability, grouped isolated strains into a main group independently of their origin, consistent with the observed gene flow between the two geographical areas among matrices (air, must and wine) and vintages (2009, 2010 and 2011). Likewise, the PCA distribution did not cluster samples collected during the 2011 vintage and from air in the minor group. DISCUSSION Some considerations about the experimental approach adopted in this work have to be noted. Firstly, the different protocols applied to sample air, must and base wine, and the plating technique used for the enumeration and isolation of the yeasts, do not allow accurate determination of the actual biodiversity present in the different materials or to make comparisons among them. However, the attention that has been spent maintaining the same places and procedures of sampling corroborates the value of the obtained results and their representativeness as concerns the permanence of species and strains in fourteen different sites for three consecutive years. In particular, the growth conditions of the agar plates to collect micro-organisms in 368 Microbiology 161

8 Autochthonous yeasts may not exist in wine environments Fig. 3. UPGMA dendrogram obtained by cluster analysis of interdelta region profiles of 270 S. cerevisiae isolates collected from air, must and wine samples during the 2009, 2010 and 2011 vintages in the Franciacorta and Oltrepò Pavese areas, and of 48 S. cerevisiae isolated from commercial strains. The 98.0 % value (dashed line) represents the discrimination threshold (scale bar corresponds to 5 % similarity). The empty triangles represent the wild isolates; the filled circles represent the strains isolated from starter cultures. air were highly selective, so that an underestimation of the actual abundance of yeasts may have occurred. These selective conditions were preferred because preliminary tests had shown the invasive growth of moulds on the plates, which did not allow detection of yeast colonies. Nevertheless, contrary to what described by Garijo et al. (2011), S. cerevisiae species were isolated from the air of vineyards for the first time by adopting this protocol. Secondly, as shown by previous ecological studies on wine yeast biodiversity, the discrimination within the non- Saccharomyces taxa is limited at the species level, whereas it would be interesting to deepen knowledge at the strain level, as has been recently explored (Pfliegler et al. 2014; Vigentini et al., 2012). Regarding the interdelta regions typing by CE to detect differences in S. cerevisiae strains, the protocol set up by Tristezza et al. (2009) was confirmed 369

9 370 Microbiology 161 Table 2. Distribution of S. cerevisiae isolates collected from air, must and wine samples during 2009, 2010 and 2011 vintages in two Lombard vine-growing areas The isolates underlined are those recognized as commercial starter strains by d-pcr typing technique. Year of isolation Isolates in Franciacorta area Isolates in Oltrepò Pavese area Vineyard/cellar Air Must Wine Vineyard/cellar Air Must Wine 2009 A 610, 619, 672, 525, 797, 798, 825, , 748, 795, 796, 837, 839, 844, 847, 850 G 620, 621, , 606, 607, 611, 617, 622, 624 B 782, 661, 726, 833, , 813, 737, 559 H , 808, 809, 810, 811, 814, 71, 612 C 640, 650, 790, 824, 831, 758, 788, 799, 843, 604, I 842, 793, , 832, D 900, , 768, 794, 838, 841 J 792, 802, , 521, 625 E 812, 834, K 601, 515, 615, , 510, F , 787, 789, 533, 840, 603, L 829, , 785, 806, 815, 816 M , 820, , 786, 817, 818, 819, 821, 823 N , 803, 845, 846, 849, A 662, , 655, 656, 657, 678 G 670 B 544, 660, 667 H 646, 675, , 691 C 627, 631, 658, 659, 663, 681 I 628, 643, 644, 645, , 671, , 693 D 635, 652, 653, 679, 680, J 634, 639, 647, 688, , 695 E 632, 641, 651, 666, 668, K 687, , 684 F 637, 642, 648, 649, , 636 L , 602, 626 M 614 N A 638, 696, 697, 729, 730, 578, 724, 727, 728, 755 G , 590, , 745, 746, 752 B 710, 731, 732, , 756, 581 H 772, 774, , 741 C 700, 701, , 718, 757 I , 743 D 713, 719, 722, , 704, 706, 715 J 770, , 769 E 698, 711, 747, , 709 K 733, 775, , 766 F 699, 712, 714, 720, 721, , 708, L M 773, 776, , 761 N 764, , 760 Starter Pascal Biotech, AEB group 899, 856, 857, 858, 859, 860, 861, 865, 868, 871, 876, 877, 879, 880, 883, 892 cultures Anchor Yeast, Intec 862, 864, 866, 869, 881, 884, 886, 889, 891, 894 I. Vigentini and others

10 Autochthonous yeasts may not exist in wine environments Table 2. cont. Isolates in Franciacorta area Isolates in Oltrepò Pavese area Year of isolation Vineyard/cellar Air Must Wine Vineyard/cellar Air Must Wine DSM, Corimpex 898, 867, 870, 878, 882, 887, 888, 890 Laffort 895, 896 Lallemand 863, 874, 885, 897 Institut Oenologique de Champagne, Perdomini 852, 853, 854, 855, 872, 873, 875, 893 G1 Fig. 4. Inferred population structure for K52 obtained by d-pcr profiles of 223 S. cerevisiae strains using the model-based program STRUCTURE. G1 and G2 indicate two estimated ancestral genetic clusters. The y-axis shows the estimated membership proportion. Each sample is displayed as a vertical line divided into differently coloured segments representing the estimated membership proportions in the two ancestral genetic clusters, where G1 is red and G2 is green. to be reliable and robust, even if the index of discrimination obtained from our results was lower (98.7 %) than that measured by the original authors (99.8 %). Commercial yeasts are easily traceable, thanks to the application of this technique. The exploitation of the indigenous microbiota is a current topic in food quality management, in particular when spontaneous fermentations are involved in wine processing (Di Maio et al., 2012; Settanni et al., 2012). Such a trend supports safeguarding of the diversity of the local products, and has a noteworthy impact in trade, especially by those consumers seeking typical foods. In this context, the recognition and preservation of micro-organisms present in vineyards and cellars is a strategic activity for the oenologist, who aims to express their own terroir in their products. Nevertheless, what exactly is meant by autochthonous yeast is still a controversial question among researchers: it is objectively assumed that a strain should originate in a site and persist in it for a certain period. However, where should we place the boundary line in determining the membership of a strain to a territory? Shall we look at the walls of the cellar, the hill planted with the vines, or at the land included in a valley or an island? Additionally, how long does it take to consider a strain as a native micro-organism of that area? Finally, the term indigenous refers to the ability to isolate the same strain identified in the course of different vintages. Recent works that monitored yeast populations for at least three years, and in which molecular techniques suitable for discrimination at strain level were used, are limited. Analysing the results presented in the work of Versavaud et al. (1995) on the distribution of S. cerevisiae strains in the wineproducing area of Charentes, it is possible to point out that several dominant strains frequently appeared in a specific year for different sites, and only a few of them could be retrieved in different vintages. Torija et al. (2001) reported that yeast populations were different every year, though some Saccharomyces strains were found over three consecutive years in the same cellar, indicating that a G

11 I. Vigentini and others natural microbiota was consistently found in the wineries. Interestingly, the appearance of new strains within a same vintage occurred in different cellars located in regions geographically distant by about 50 km. Beltran et al. (2002), in a six year follow-up study, discovered that most of the new strains of S. cerevisiae were isolated in the same year, and that the predominance of a specific strain was more influenced by the vintage than by the grape variety or wine making process. Demuyter et al. (2004), which studied the dominance of S. uvarum during spontaneous fermentation in an Alsatian winery, also stated that the yeast populations on grapes changed from year to year, and that new non-resident strains appeared in the must during the winemaking process. Schuller & Casal (2007) demonstrated that the genetic differentiation among S. cerevisiae populations in the same vineyard in consecutive years showed a similar magnitude to the differences found among the different vineyards of the same vintage. The results obtained in our survey are consistent with those of the preceding works, confuting the current opinion that there are autochthonous strains that permanently reside in vineyards or cellars. In the samples collected during three consecutive years in two different Lombard territories, a high yeast biodiversity is recognized, either at intraspecific and at interspecific level, in the case of S cerevisiae species. The effect of the vintage overcomes the effect of the geographical area of isolation, since dominant species found in air and must change each year. Moreover, the analysis of yeast populations provided evidence of significant population structure within the sample, showing that the diversity of microbial communities could be affected by vintage. In addition, new strains of S. cerevisiae appear simultaneously in both territories although they are more than 100 km away from each other. In this regard, Stefanini et al. (2012) have recently highlighted the specific role of social wasps in the environmental dispersion of yeast cells and in the evolution of S. cerevisiae populations. Surprisingly, no strain was isolated in the same vineyard or cellar during different years, challenging the idea that yeast populations are stable in a wine environment over time (Ciani et al., 2004; Cordero-Bueso et al., 2011b). This outcome is also corroborated by the work of Bokulich et al. (2013), which observed seasonal fluctuations of the surface microbial communities in a winery equipment. Actually, compliance to the hygiene control system based on the Hazard Analysis Critical Control Points principles, through the rigorous application of cleaning and disinfection procedures, should counteract the permanence of microorganisms in oenological plants. ACKNOWLEDGEMENTS The authors gratefully thank Dr Rossana Tonesi for helpful advice, and the personnel of the wineries involved in this work for their precious collaboration, particularly the oenologists Giacomo Barbero, Stefano Capelli, Alice Colombo, Guido Gandossi, Michele Ferrari, Silvia Filisetti, Simone Fiori, Andrea Rossi, Luca Rossi, Alessandro Schiavi, Silvia Uberti, Giuseppe Vezzoli, Raffaello Vezzoli and Daniele Zangelmi, and the students Andrea Barbieri, Shirley Barrera Cardenas, Fabrizio Cadei and Federico Prevadini. 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