## 4 Discussion  
_Terroir_ is an expression in viticulture used to describe the unique contribution of regional features such as cultivar, vintage, and climate, that define wine sensory characteristics and product identity in a particular region. Although much is known about _terroir_ relative to _Vitis vinifera_ varieties, much is unknown about hybrid grapes. In this work, 29 species were identified from 120 isolates and distinct patterns of microbial composition in three PA vineyards were observed. In support of a parallel study on Chambourcin microbiome, these results highlight unique differences in microbial populations even within a small geographic area (radius about 90 km) [60]. In 15 vineyards across southern Australia (5-400 km part), distinct microbial profiles were found in environmental samples collected from soil, plant, must, and across fermentation stages [61]. Previous studies also demonstrate that microbial populations can impact wine quality [62]. For example, _Starmerella bacillus and Metschnikowia pulcherrima_ isolated from multiple regions of Italy were found to increase production of higher alcohols such as \(\beta\)-phenylethyl alcohol corresponding to floral odor through coinoculation [12]. _Kazachstania aerobia_ and _K. servazzii_ in Shiraz grape must from southern Australia were found to have increased production of esters, such as phenylethyl acetate and isoamyl acetate associated to rose and fruity aroma [63]. These examples prompted us to ask whether microbial populations on Chambourcin hybrid grapes in PA vineyards can shape wine characteristics of the region. _Hanseniispora_ spp. and _Pichia_ spp. were the most dominant species identified during spontaneous fermentation of Chambourcin with relative abundances of 42% and 11% of total isolates, respectively (Figure 1 and Table S1). Previous studies have reported the dominance of _Hanseniispora_ and _Pichia_ species on various grape varieties (i.e., _V. vinifera_, _V. labrusca_, and hybrid grapes), in grape must, and at early stages of fermentation [30; 38; 64; 65; 66]. The abundance of _Hanseniispora_ spp. and _Pichia_ spp. appear as core non-_Saccharomyces_ yeasts on wine grapes and could be related to nutrient availability of mature grape berries which supports fast growth of these species while suppressing other microorganisms [62]. In early stages of spontaneous fermentation, high abundance of \(H\). _uvarum_, _P. klyuveri_, _P. novegenisis_, and _P. guilliermondii_ were found on _V. vinifera_ (Iashel and Bordeaux), and hybrid grapes (Zweigelt, cross between St. Laurent and Blaufrankisch) [65; 66; 67]. Therefore, our findings on the dominance of _Hanseniispora_ spp. and _Pichia_ spp. further suggest these two species are the conserved components in microbial _terroir_ of Chambourcin hybrid grapes. Tolerance to sulfite and ethanol are two characteristics important in non-_Saccharomyces_ strains for potential use in winemaking. In particular, _P. kudriazvezii_ PSWCC102 can tolerate 10% (\(v/v\)) ethanol comparable to the control strain _S. cerevisiae_, whereas _Hanseniispora_ species PSWCC70 and PSWCC64 can tolerate up to 8% (\(v/v\)) ethanol. Several studies have indicated increased ethanol tolerance of up to 6% in some non-_Saccharomyces_ yeasts such as _H. guilliermondii_ and _C. stellate_[68]. Although there are fewer studies on mechanism of higher ethanol tolerance on non-_Saccharomyces_ yeasts, increased ethanol tolerance in _S. cerevisiae_ has been positively linked to the improvement of fermentation capacity and production of wine important flavor compounds [69; 70]. Thus, it would be interesting in future studies to add _H. uvarum_ PSWCC70, _H. ountiae_ PSWCC64, and _P. kudriazvezii_ PSWCC102 in sequence or in combination with _S. cerevisiae_ to assess improvement of flavor profile in wine fermentation.