## 3 Results and Discussion
### Microbial Community Analysis  
#### 3.2.1 The Dynamic Composition of Microbial Communities during Fermentation  
Venn charts can be used to analyze the common and unique microorganisms based on Operational Taxononical Units (OTUs) in multiple groups or samples and can show the similarity and divergence of microbial compositions in samples [24]. Results showed that bacteria from the CS (Caosha, round 1b) samples included 229 microbial genera, bacteria from the C2 (round 2) sample included 235 microbial genera, and bacteria from the C3 (round 3) sample included 205 microbial genera (Figure 3a). These samples shared 160 bacterial genera, and CS samples contained 23 unique bacterial genera, C2 samples included 25 unique bacterial genera, and C3 samples contained 15 unique bacterial microbial genera. The diversity of fungi was slightly lower than that of bacteria (Figure 3b). CS samples included 141 fungal genera, C2 samples contained 169 fungal genera, and C3 samples included 209 fungal genera. These three groups of samples shared 106 genera, while CS samples contained 7 unique fungal genera, C2 samples included 22 unique fungal genera, and C3 samples contained 60 unique fungal genera (Figure 3b). Bacterial composition analysis indicated that the dominant bacterial genera were mainly _Lactobacillus_, _Oceanobacillus_, and _Virgibacillus_. The high abundance bacterial genera in the upper, middle, and bottom layers of fermented grains were _Pediococcus_, _Virginacillus_, and _Oceanobillus_ at the beginning of fermentation in round 1b (Figure 4a). During ferment  
Figure 3: Analysis of the common and unique microorganisms from fermented grains at the genus level. (**a**) bacteria. (**b**) fungi. CS, round 1b. C2, round 2. C3, round 3.  
tation, the abundance of these three genera gradually decreased, and the abundance of _Lactobacillus_ significantly increased and continued to the end of fermentation. The amount of _Lactobacillus_ accounted for more than 60% of the total bacteria in the middle and late stages of fermentation. At the beginning of fermentation in round 2, the main microorganisms in the upper, middle, and bottom layers of the fermented grains were _Oceanobacillus_, _Virgibacillus_, and _Kroppenstedtia_. During fermentation, the abundance of these three genera gradually decreased, while that of _Lactobacillus_ increased and showed high abundance in the middle and bottom layers of fermented grains in the middle stage and the upper, middle, and bottom layers of fermented grains in the late stage of fermentation (Figure 4a). Compared with round 1b, the increased ratio of _Lactobacillus_ in round 2 was relatively slow. Compared with rounds 1b and 2, at the beginning of round 3, the abundance of _Lactobacillus_ dominated in the upper, middle, and bottom layers of the fermented grains (both exceeded 57.22%), followed by _Oceanobacillus_ and _Virgibacillus_, whose abundance were only 3.93-11.71% and 1.06-11.22%, respectively. During fermentation, the microbial abundance of _Lactobacillus_ decreased, and the abundance of _Oceanobacillus_, _Virgibacillus_, _Kroppenstedtia_, and _Rhodococcus_ increased, among which the microbial abundance of _Oceanobacillus_ and _Virgibacillus_ increased significantly, such as in sample C3_CJZ and C3_CJX, the abundance of _Oceanobacillus_ was 19.06% and 26.00%, respectively, and that of _Virgibacillus_ was 15.34% and 18.62%, respectively (Figure 4a). Fungal composition analysis indicated that the dominant genera were _Issatchenkia_, _Byssochlamys_, and _Saccharomyces_. In round 1b, the dominant fungi at the beginning of fermentation were _Byssochlamys_, _Saccharomyces_, and _Issatchenkia_ (Figure 4b). Thereafter, _Saccharomyces_ and _Issatchenkia_ became dominant fungi and lasted until the end of fermentation. In round 2, _Issatchenkia_, _Byssochlamys_, and _Saccharomyces_ were the dominant fungi and lasted until the end of fermentation, and in this round, the abundance of _Monascus_ was also high (2.74-23.46%).