## 3 Results and Discussion
### Succession of Microbial Communities and Microbial Interactions
of _Clostridium_ in sample 3 was higher than that in sample 4, and sample 2 showed the lowest relative abundance, which also reflected that the amount of microorganisms initially added had a significant impact on the microbial succession in the fermentation process. The abundance of _Capriciproducens_ gradually increased in samples 3 and 4, and the highest abundance was 0.26%, in sample 3, on the 28 th day. At the genus level, 162 fungal genera were detected in all samples (Figure 5d). According to the Venn analysis of fungal microorganisms (Figure 5c), there were 108 fungal genera in sample 1, 113 fungal genera in sample 2, 84 fungal genera in sample 3, and 99 fungal genera in sample 4, of which 59 fungal genera were common to all samples. In addition, there were eleven, thirteen, four, and fourteen specific fungal genera in samples 1, 2, 3, and 4, respectively. There were nineteen genera with a relative abundance above 1% in all samples, including _Saccharomyces_, _Apergillus_, _Trichosporon_, _Saccharomyces_, _Plecdsophenella_, _Thermoiscus_, _Byssochlamys_, _Wickerhamomyces_, _Cldosporium_, _Thermomyces_, _Candidia_, _Wallemia_, _Moniscus_, _Rasamsonia_, _Isastchenkia_, _Papililotrema_, _Kodamaea_, _Mortierella_, and _Meyerozyma_ (Figure 5d). _Saccharomyces_ and _Apergillus_ were the most important fungal genera in the fermentation process, and they were also the fungal microbes of the designed microbial combination. In all the samples, _Saccharomyces_ grew rapidly and reached the highest abundances of 11.7%, 27.6%, 68.3%, and 89.7%, in samples 1,2,3, and 4, respectively, on the 14 th day of fermentation, while the abundance decreased and remained stable in the middle and late fermentation stages. The genus _Saccharomyces_ is usually recognized as one of the most important genera for ethanol production [43; 44], while the production of ethanol was mostly performed in the early and middle stages of fermentation, thereafter, the abundance of _Saccharomyces_ decreased in the middle and late stages. During the whole fermentation process, _Saccharomyces_ showed a relatively high abundance in sample 4, followed by sample 3, sample 2, and sample 1 (Figure 5d). As for _A Aspergillus_, the abundance was low in the early stage of fermentation in sample 3 and sample 4, and gradually increased and stabilized in the middle and late stages, with relative abundances of 41.9% and 26.6%, respectively (Figure 5d). In sample 2, the abundance of _Apergillus_ was slightly higher in the middle stage of fermentation than that in the late stage, but the maximum abundance was only 9.29% (Figure 5d). _Apergillus_ shows a good ability to saccharify starch, and the products could serve as the carbon sources for the growth of other microorganisms in the samples. The abundance of _Apergillus_ in sample 3 was continuously higher than that in other samples in the middle and late stages of fermentation, generating a higher content of reducing sugar (Figure 3d). _Monascus_ was also added to the fermentation system, it showed a relatively high abundance in sample 3 (4.81%) and sample 4 (4.03%) on day 0, decreased to 0.58 % and 0.04% on the 14 th day, and then remained stable (Figure 5d). This indicates that the _Monascus_ in fermentation system was unable to occupy a relatively high abundance during the fermentation process. During Baijiu fermentation, the interaction between microorganisms serves as one of the main forces for microbial dynamic fluctuations, and affects the stability of the microbial ecosystem [45]. The interactions between microorganisms diverged in different fermentation systems, and caused microbes to perform different metabolic pathways, resulting in the divergence of the production and stabilization of flavor compounds. However, complex interactions between microorganisms during fermentation has not been scientifically investigated.