## 3 Results and Discussion
### Comparison of Microbial Diversity among Samples  
HTS was used to identify the succession of the microbial community during the Cabernet Sauvignon fermentation. A total of 1,053,790 (average length = 354 bp) quality filtered sequencing reads corresponding to the ITS1F_ITS2R regions of fungal ITS rRNA genes were obtained. All sequences were clustered into 366 OTUs with 97% similarity (Supplementary Figure S1). These sequences were annotated into 299 fungal species. The alpha diversity indices, such as Chao, ACE, Shannon, Simpson and Good's coverage, were used to determine microbial diversity (Supplementary Table S1). Good's coverage of all samples reached 99%, indicating that the data coverage provided a satisfactory description of the microbial diversity. The dominant phylum across the entire eukaryotic population was _Acosomycota_, followed by _Basidiomycota_ and other fungi. Moreover, the dynamics of microbial populations of all the samples at phylum level were very similar, but the relative abundances varied during the fermentation and among different starters (Figure 1A). The distribution of the fungal genus with relative abundance above 1% is presented in Figure 1C. Fourteen fungal genera were detected in sixteen samples. With respect to the overall proportion, _Saccharomyces_, _Botrytis_, _Cladosporium_, _Vishniacozyma_ and _Alternaria_ were the most prevalent fungal taxa throughout the fermentation. There were 135 fungal genera in fermentation by CEC01; among them, 24 genera were unique, which was higher than other starters, followed by F15 (Figure 2A). The lowest number of fungi was observed in the fermentation broth inoculated with 796. A total of 65 genera coexisted in the fermentation process of four strains. CECA and CEC01 shared the most genera in the must, with 12 genera. Figure 1: Microbiota composition. (**A,B**): The Circos graphs of fungi (**A**) and bacteria (**B**) at the phylum level in 20 samples. (**C,D**): Relative abundance of fungi (**C**) and bacteria (**D**) on the genus level. _Botrytis_ and _Cladosporium_ were the predominant fungal genera in grape juice. They have also been found in grape skins and spontaneous fermentation [17; 18]. After fermentation started, _S. cerevisiae_ grew and rapidly dominated the community, while other species underwent drastic decreases in relative abundances during the fermentation. However, the relative abundance of Botrytis and Cladosporium in F2d was higher than that in other experimental groups, which was related to the slow start of fermentation by F15, and the inhibitory effect of lower alcohol concentration on microorganisms was weaker. For bacteria diversity, all quality filtered sequences were clustered into 870 OTUs (97% similarity level) (Supplementary Figure S2), and 25 bacterial phyla were detected in alcoholic fermentation. The richness and diversity of the microbial communities in each sample were assessed by alpha diversity. The ACE and Chao diversity indices showed that the abundance of bacteria in the samples was remarkably higher than that of fungi (Supplementary Table S2). Concerning the prokaryotic communities, the dominant phyla were _Proteobacteria_, _Firmicutes_, _Actinobacteria_ and _Bacteroidota_ (Figure 1B). The members of underrepresented phyla were grouped together in the artificial group \"Others\". A related study [19; 20] indicated that the dominant phyla on the surface of wine grapes are _Proteobacteria_, _Actinobacteria_ and _Firmicutes_. Most of the bacteria in the fermentation process of the sample may have come from the berry epidermis and vineyard environment [21]. As a reflection of the microbial community dynamics, the relative abundances of all prokaryotic communities varied in time and among different samples. _Firmicutes_ (33.4%) was dominant in the fermentation process of F15; the dominant phylum in CECA was _Actinomycetes_. A total of 476 bacterial genera were detected in the 16 groups, of which 21 bacterial genera with relative abundances greater than 1% were selected for further analysis (Figure 1D).