## 3 Results and Discussion
### Microbial Community Composition in Douchi Products  
The microbial community composition was different among the douchi products. As shown in Figure 1a, _Frimicutes_ was the dominant microorganism, followed by _Proteobacteria_. It is worth noting that _Frimicutes_ made up nearly 99% of the community in DC-2, DC-5, DC-6, and DC-7. The ratio of _Frimicutes_ to _Proteobacteria_ was almost 1:1 in DC-1, while it was 6:1 in DC-3 and 10:1 in DC-4. The fungi in DC-3 and DC-4 were not amplified because there were fewer of them in the sample. At the phylum level (Figure 1c), there were three phyla with relative abundances of \(>\)1%, including _Ascomycota_, _Mucromycota_, and _Basidiomycota_. These phyla were also found to be major components of microbial flora in Chinese fermented vegetable foods, fermented fish, and chestnut rice wine [19; 21; 22]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Type** & **Sample** & **Chao1** & **Simpson** & **Shannon** & **Ace** & **Goods\_Coverage** \\ \hline \multirow{4}{*}{fungi} & DC-1 & 120.31 & 2.13 & 0.55 & 121.56 & 0.9999 \\  & DC-2 & 113.65 & 3.13 & 0.81 & 114.21 & 0.9999 \\  & DC-5 & 97.78 & 0.97 & 0.26 & 95.72 & 0.9999 \\  & DC-6 & 105.63 & 1.93 & 0.51 & 98.23 & 0.9999 \\  & DC-7 & 92.88 & 1.61 & 0.40 & 94.80 & 0.9999 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 1: The relative abundance changes of the bacteria in douchi samples at phylum (**a**) and genus levels (**b**) and fungi in douchi samples at phylum (**c**) and genus levels (**d**). At the genus level of bacteria (Figure 1b), the dominant genus was _Bacillus_, accounting for 15.68-99.34% in all the samples. The genera with relative abundances of >1% were _Bacillus_, _Pseudomonas_, _Tetragonococcus_, and _Weissella_, while the rest of the genera had very low abundances. _Bacillus_ spp. were also the dominant bacterial taxa in many fermented soybean products and the wine industry [21], and they contributed flavor through amylase and protease activities. [PERSON] [23] reported that _Bacillus_ may prefer anaerobic or microaerophilic conditions. In our study, the abundances of _Bacillus_ in DC-2, DC-3, DC-4, and DC-7 exceeded 80%; it may be related to douchi that was not agitated during the post-fermentation period. Research has also indicated that _Pseudomonas_ improves the flavor of douchi by producing more kinds of protease, lipase, and lecithin enzymes [24], and in our study, the relative abundances of _Pseudomonas_ in DC-1 (50.54%), DC-3 (14.27%), and DC-4 (7.54%) were all above 1%. _Tetragonococcus_ and _Weissella_ were lactic acid bacteria (LABs) that have been detected in a variety of fermented foods and play important roles in flavor generation, and these were involved in the production of lactate, acetate, and ethanol [23]. _Tetragonococcus_ is a halophilic LAB, which has been noted as being the dominant bacteria of traditional fermented soybean products in China, Japan, South Korea, and other southeast Asian countries. In our study, DC-5 had a high level of _Tetragonococcus_ (83.08%); meanwhile, _Weissella_ (56.04%) was high in DC-6. Some bacterial species were unique in each sample because of different raw materials, processing technologies, and fermentation environments [25]. The fungal phylum level is shown in Figure 1d; the number of major fungi was 10, involving _Aspergillus_, _Mucor_, _Penicillium_, and _Trichothecium_. Compared with the bacterial variation, the variation in the fungal composition was more complex, with the most dominant microorganisms varying from sample to sample. In DC-1 and DC-7, _Aspergillus_ was the dominant fungus, accounting for 65.88% and 77.18%. _Aspergillus_ has been shown to be a major fungal group in ganjiang (a Korean traditional soy sauce) [26], and it secreted a variety of enzymes that contribute to the texture and flavor of fermented foods [27]. [PERSON] [28] claimed _Aspergillus_ and _Zygosaccharomyces_ were the predominant fungi in Chinese fermented soybean paste, which was somewhat different from this study.