## 3 Results and Discussion
### Changes in Bacterial Flora during Apo Pickle Fermentation  
The natural fermentation process of Apo pickle is dependent on microorganisms found naturally in _B.nupus_, and research into the variations in the bacterial population throughout the fermentation phase of Apo pickle can give a theoretical foundation for further inoculation fermentation of Apo pickle. We studied the bacterial communities in different stages of the VBA and TBA fermentation process and drew the relative abundance map (Figure 3B,C). At the phylum level, the sum of the relative abundance ratios of _Firmicutes_ and _Proteobacteria_ was above 97% in the whole process, and the content of _Firmicutes_ kept rising, becoming the dominant phylum (Figure 3B). This result was the same as that of some traditional fermented products in China, such as pickled radish [30], and fermented sausage [31]. The main genera in the fermentation process of VBA and TBA included _Lactobacillus_, _Weissella_, _f_Enterobacteriaceae_Unclassified, _Exiguobacterium_, _Aerococcus_, _Pseudomonas_, and _f_Erwiniaceae_Unclassified. LAB is a key player in the fermentation of Apo pickle [22]. In the initial stage of fermentation, _Weissella_ was the LAB dominant genus, and it was heterotypic fermented LAB, which can use the phosphoketo  
Figure 3: The Illumina HiSeq sequencing of Apo pickles. (**A**) Bacterial community OTU rarefaction curves; (**B**) the bacterial community of VBA and TBA at the phylum level; (**C**) the bacterial community of VBA and TBA at the genus level.  
-like pathway to ferment carbohydrates and produce ethanoic acid, CO\({}_{2}\), ethanol, and lactic acid, thus effectively improving the flavor [32]. At 5 d, the relative abundance of _Weissella_ was highest in VBA and TBA, reaching 45.53% and 50.67%, respectively. The relative abundance of _Weissella_ fell gradually as lactic acid accumulated and acidity increased, reaching 10.19% and 19.42% at 35 d, respectively. _Lactobacillus_, a homoformentative LAB with great acid resistance and stringent anaerobicity, gradually became the dominating genus in the middle and late phases of fermentation. Pyruvate produced during this fermentation was converted into lactic acid by lactate dehydrogenase (LDH), which made the pH decrease. The relative abundance of _Lactobacillus_ in VBA reached 78.45%, while that in TBA reached 58.51% at 35 d. In the whole fermentation process, the relative abundance of LAB in VBA > TBA, which may be because the vacuum bag used in the experiment has better gas barrier performance than plastic bottles and can better ensure an anaerobic environment. This needs further exploration. The f_Enterobacteriaceae_Unclassified and _Pseudomonas_ were the non-LAB dominant genera in samples, with high relative abundance in the early stage; their growth was inhibited by the increase of _Lactobacillus_ in the fermentation process, which was similar to the research results from [PERSON] et al. [33].  
The above conclusions show that the dominant genera of VBA and TBA are the same in the fermentation process, but the content of LAB, which plays an important role in fermentation, is different. The LEfSe analysis of VBA during the fermentation is shown in Figure 4. The dominant genera were _Lactococcus_, _Staphylococcus_, _Klebsiella_, and _Weissella_ at 5 d, _Aerococcus_ at 10 d, and _Lactobacillus_ at 35 d.  
Figure 4: VBA LÉfSe analysis.