## 3 Results and Discussion
### Microbial Community Analysis
#### 3.2.2 Microbial Interactions during Fermentation  
Microbial composition analysis showed that the microbial diversity of the fermented grains in the upper, middle, and bottom layers was differentiated, indicating that the solid-state fermentation of the fermented grains showed the characteristic of heterogeneity [26] and that dividing the fermented grains into different layers could better reveal the microbial composition and abundance. The succession of microbial abundance was related to environmental conditions such as temperature, oxygen concentration, and the content of nutrients such as oligosaccharides, monosaccharides, short peptides, and amino acids that served as the metabolic substrates for microorganisms [27; 28]. In addition, the interaction between microorganisms also provided an important driving force for the fluctuation of microbes [29]. In this part, the microbial interaction relationships were investigated between bacteria and bacteria, bacteria and fungi, and fungi, respectively. Results showed that there was a significant interaction between bacteria; for example, _Lactobacillus_ showed negative interaction with all other bacterial genera, while _Oceanobacillus_ and _Virgibacillus_ both showed positive interaction with most of the bacteria except for significant negative interaction with _Lactobacillus_ (Figure 7a). This might be caused by the high abundance of _Lactobacillus_ in most stages of the fermentation process. A high abundance of _Lactobacillus_ competitively consumed a large amount of nutrients in the fermentation system, thus inhibiting the growth of other microorganisms (Figure 7a). The relationships between the three dominant fungal genera and the left fungal genera were relatively complicated because the abundance of dominant fungi was not as high as the abundance of _Lactobacillus_ in bacteria (Figure 7b). For example, _Issatchenkia_ showed significant positive interaction with _Pichia_, and negative interaction with _Byssochlamys_, _Aspergillus_, _Debaryomyces_, and _Piskurozyme_, while had no significant interaction with _Saccharomyces_, one of the dominant fungi (Figure 7b). _Byssochlamys_ showed positive interaction with most fungal genera, such as _Monascus_, _Thermoascus_, _Thermouscus_, _Aspergillus_, _Leithecium_, _Rasamsonia_, unclassified_Dipodascaceae_, _Pencillium_, _Wallenia_, _Trichospor_, unclassified_Saccharomyces_, _Naganishia_, _Geotrichum_, _Debaryomyces_, _Cystofilobasidium_, _Cladosporium_, _Rhodotorula_, _Dipodascus_, unclassified_Microascaceae_, _Gymnoascus_, _Piskurozyme_ and _Pithoascus_, and showed negative interaction only to _Isatchenkia_, _Saccharomyces_, _Kodamaea_, _Hyhphicchia_, and _Cyberlinera_. _Saccharomyces_ only showed positive interaction with _Zygosaccharomyces_ but had negative interaction or no significant interactions with most fungal genera (Figure 7b). Figure 6: PLS-DA analysis of the microbial genera in the fermented grains during the sauce-flavor Baijiu manufacturing process. (**a**) bacteria. (**b**) fungi. CS, round 1b. C2, round 2. C3, round 3. Compared with complex positive or negative interactions between bacteria and bacteria and fungi and fungi, the interactions between bacteria and fungi were relatively insignificant. Figure 7: Reciprocal interaction analysis of the microorganisms in the fermented grains during the manufacturing process of sauce-flavor Baijiu. (**a**) the three dominant bacteria genera with other bacteria. (**b**) the three dominant fungi genera with other fungi. (**c**) the three dominant fungi genera with bacteria. (**d**) the three dominant bacteria genera with fungi. * 0.01 < \(p\leq\) 0.05, *** 0.001 < \(p\leq\) 0.01, *** \(p\leq\) 0.001.  
icant (Figure 7c,d). Results of 3 dominant fungal genera with bacteria indicated _Issatchenkia_ showed negative interaction with the bacterial genera _Nocardiopsis_ and _Amphibacillus_ and no positive or negative interaction with the left bacterial genera (Figure 7c).