Abstract

Vitis vinifera L. cv. Corvina grape forms the basis for the production of unique wines, such as Amarone, whose distinctive sensory features are strongly linked to the post-harvest grape withering process. Indeed, this process increases sugar concentration and changes must characteristics. While microorganisms involved in must fermentation have been widely investigated, few data are available on the microbiota of withered grapes. Thus, in this paper, a whole metagenome sequencing (WMS) approach was used to analyse the microbial consortium associated with Corvina berries at the end of the withering process performed in two different conditions (“traditional withering,” TW or “accelerated withering,” AW), and to unveil whether changes of drying parameters could have an impact on microbial diversity. Samples of healthy undamaged berries were collected and washed, to recover microorganisms from the surface and avoid contamination with grapevine genetic material. Isolated DNA was sequenced and the data obtained were analyzed with several bioinformatics methods. The eukaryotic community was mainly composed by members of the phylum Ascomycota, including Eurotiomycetes, Sordariomycetes, and Dothideomycetes. Moreover, the distribution of the genera Aspergillus and Penicillium (class Eurotiomycetes) varied between the withered berry samples. Instead, Botryotinia, Saccharomyces, and other wine technologically useful microorganisms were relatively scarce in both samples. For prokaryotes, 25 phyla were identified, nine of which were common to both conditions. Environmental bacteria belonging to the class Gammaproteobacteria were dominant and, in particular, the TW sample was characterized by members of the family Pseudomonadaceae, while members of the family Enterobacteriaceae dominated the AW sample, in addition to Sphyngobacteria and Clostridia. Finally, the binning procedure discovered 15 putative genomes which dominated the microbial community of the two samples, and included representatives of genera Erwinia, Pantoea, Pseudomonas, Clostridium, Paenibacillus, and of orders Lactobacillales and Actinomycetales. These results provide insights into the microbial consortium of Corvina withered berries and reveal relevant variations attributable to post-harvest withering conditions, underling how WMS could open novel perspectives in the knowledge and management of the withering process of Corvina, with an impact on the winemaking of important Italian wines.

Highlights

  • Grape naturally hosts a reservoir of microorganisms that may be transferred into the winery and affect the vinification process, influencing wine quality and storage (Mills et al, 2007)

  • Several analyses were performed to analyse the characteristics of the berry microbial communities: (i) mapping shotgun reads against MG-Rapid Annotation Subsystem Technology (RAST) database and a database of species-specific genomic regions; and (ii) assembling sequences into scaffolds

  • A number of studies have demonstrated that the microbial communities on grape surfaces play an important role in grape quality, yield, and in winemaking, contributing to a regional terroir (Barata et al, 2012; Bokulich et al, 2014; Capozzi et al, 2015; Zarraonaindia et al, 2015)

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Summary

Introduction

Grape naturally hosts a reservoir of microorganisms that may be transferred into the winery and affect the vinification process, influencing wine quality and storage (Mills et al, 2007). Species present on sound ripe berries have been reported to belong mainly to the group of oxidative basidiomycetous yeasts, such as Cryptococcus spp., Rhodotorula spp., Sporobolomyces spp., and Filobasidium spp., as well as to the dimorphic ascomycetous black yeast, Aureobasidium pullulans (Prakitchaiwattana et al, 2004; Magyar and Bene, 2006; Barata et al, 2008). These yeasts are ubiquitous in the vineyard environment and they are typically associated with grapes, phyllosphere, and soil (Setati et al, 2012; Gilbert et al, 2014). Saccharomyces cerevisiae, the most relevant fermentative wine yeast, is mostly present in low number and low frequencies, even in damaged berries (Fleet, 2003)

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