## 3 Results and Discussion
### Microbial Structure  
The sequences comprising the total reads corresponded to five domains, eight king-doms, 47 phyla, 99 classes, 207 orders, 353 families, 706 genera, and 2068 species, of which four domains were known. These four were identified to be bacterial, fungal, archaeal and virus domains, of which the bacterial domain had the highest proportion at 99.31% and the lowest was for the fungal domain. In addition, eight kingdoms in all samples were detected, of which the major phyla were _Firmicutes_ and _Ascomycota_ with _Firmicutes_ the most abundant, contributing to over 98% in all samples, consistent with previous reports of other fermentation vegetables [24; 25]. Further, it was interesting to note that with the progress of fermentation, the content of _Ascomycota_ decreased gradually in the red radish samples, but there was no obvious change in the cabbage samples. The major classes, order and family were _Bacilli_ and _Saccharomycesces_, _Lactobacillus_ and _Saccharomycesces_ and _Lactobacillusaceae_ and _Saccharomycescetaceae_, consistent with the phyla identified. As for the genus level, a total of 706 microbe genera were detected, of which 319, 521 and 664 genera were detected in the initial red radish and cabbage brines, respectively. Among them, 303 genera occurred in all paocai samples, wherein 38 genera only appeared in the red radish samples, 171 genera only appeared in the cabbage samples and 303 genera appeared in both paocai samples (Figure 2A). The microbial diversity of paocai was found to be relatively simple, and there were only three genera with abundance more than 1% of the diversity, and they belonged to the _Lactobacillus_, _Pedicococcus_ and an unclassified _Lactobacillus_ genus. The average abundance of _Lactobacillus_ in the initial brine, red radish paocai and cabbage paocai reached 92.35%, 85.10% and 81.84%, respectively. Furthermore,  
Figure 1: **(A)** Sequence length distribution of nonredundant gene catalog. **(B)** NMDS analysis at species level. Analysis of similarities between different groups by ANOSIM **(C,D)** of red radish paocai and cabbage paocai in the 3 rd and 4 th round, separately. **(E)** LDA score of the two kinds of red radish paocai and cabbage paocai. **(F)** Wilcoxon rank-sum test of different species in red radish paocai and cabbage paocai. * 0.01 \(<p\leq\) 0.05, **0.001 \(<p\leq\) 0.01, *** \(p\leq\) 0.001. _Lactobacillus_ was the predominant bacteria in the multiround fermentation, and was found to be in agreement with other paocai studies [8]. However, with the progress of fermentation, _Lactobacillus_ gradually decreased, accounting for only 67.4% of red radish paocai at the end of the sixth round of fermentation and 69.5% of cabbage paocai. Although previous studies have different conclusions about whether _pediococcus_ is the dominant bacterium in fermented vegetables [12; 26; 27], the proportion of _Pedicoccus_ genus was found in general to be increasing along with the fermentation. Specifically, its abundance was found to increase from 2.82% to 28.37% in the red radish and 2.58% to 26.28% in the cabbage paocai brines (Figure 2B), respectively. These data indicate that although they belong to the same phylum (Firmicutes), _Pediococcus_ may be more stress-resistant or competitive than _Lactobacillus_ in the later stage of fermentation. At the species level, a total of 2068 microbial species were detected by sequencing, of which 870, 1525 and 1923 species were detected in the initial, red radish and cabbage brines. Among the detected species 826 of them occurred in all paocai samples (Figure 2C), whereas 129 species appeared only in the red radish samples, and 505 species only in the cabbage samples. A further 564 species commonly appeared in all the red radish and cabbage paocai samples, but only 11 of them were recorded with relative abundances of more than 1%.