Regional distinctiveness of wines is strongly shaped by the composition and activity of site-specific microorganisms, which is known as the microbial terroir concept. For this reason, spontaneously fermented wines are gaining popularity, whereas wines relying on inoculated fermentations with commercial yeast strains tend to standardized aroma profiles and reduced sensorical complexity. Therefore the microbial dynamcis during a spontaneous fermentation of an Austrian Grüner Veltliner from a winery in Gols (Burgenland), was analyzed using long-read amplicon sequencing. Samples of unripe grapes, mash and fermenting must (every three days) were collected, DNA was extracted and then sequenced on an Oxford Nanopore platform as 16S- and ITS-amplicons. The results show that the washed grape samples and the mash sample are
strongly affected by co-amplification of chloroplast and mitochondrial Vitis vinifera rRNA genes.Over the course of fermentation, Tatumella/Pantoea (29.78-59.02%) were the most abundant genera. At fermentation start, lactic acid bacteria of the genera Lactococcus (32.63%) and Lactobacillus/Apilactobacillus (27.43%) showed high relative abundances and decreased over time,whereas Lactiplantibacillus increased with the course of fermentation. In one sample, Gluconobacter was detected at a relative abundance of 9%. The fungal community showed a transition from Hanseniaspora at the beginning of fermentation towards a Saccharomyces-dominated community from mid to end of fermentation. The study demonstrates the potential of long-read amplicon sequencing for determining the microbial composition of spontaneously fermented wine samples, but also identifies plant-associated DNA contaminations as a technical limitation that should be improved in future studies by optimized host-depletion strategies.

Co-authors: Lukas Fürnwein, Alexandra Graf