## 3 Results
### Bacterial Compositions of Sichuan Bacons  
The relative abundances (%) of bacterial community proportions at the phylum and genus level are shown Figure 2. Firmicutes and Proteobacteria were the dominant phyla in all samples, ranging from 77.1% to 98.9%, and most samples revealed levels above 90%. Apart from these two phyla, Actinobacteria, Oxymptobacteria, and Bacteroidetes were observed in some samples at levels above 1% (Figure 2A). This agrees with research on other Chinese traditional meat products such as Chinese sausage and ham [18; 26]. At the genus level (Figure 2B), _Staphylococcus_ was the dominant genus in the basin, mountains, and plateau group bacons, covering 26.7%, 20.6%, and 22.7% of the total genus, respectively. Conversely, the relative abundances of _Lactobacillus_, accounting for 0.5%, 3.5%, and 2.5%, respectively, were much lower than those of _Staphylococcus_. Many researchers support the belief that LAB and CNS are the most active microorganisms derived from meat fermentation [5]. The previous studies focused more on _Lactobacillus_ diversity and function in Chinese traditional meat products [27], while little attention was paid to _Staphylococcus_. Moreover, the diversity of CNS in meat products is complex and variable because it is subject to multiple factors, including the type of raw muscle used, the ingredients added, and the processing conditions applied [28]. For instance, the pH increases due to the use of lactate during post-ripening, leading to replacement of the dominant species from _S. saprophyticus_ to _S. aquorum_, which is more adapted to weaker acidic environments [29]. It is reasonably believed that the role of _Staphylococcus_ in the formation of the unique flavor and quality of Sichuan bacon should be paid more attention in future research.  
In addition to _Staphylococcus_, some other predominant genera of relative abundance were observed in the samples. For instance, _Phyllobacterium_ (16.8%), _Psychroducer_ (11.5%), _Brochlorrix_ (6.5%), _Vibrio_ (6.3%), and _Defhia_ (3.2%) were the abundant genera in the basin group, which are commonly spoilage bacteria in meat products [30]. In the plateau group, the relative abundance of _Pseudomonas_ was up to 10.2%, which was much higher than the other two groups. This gram-negative bacteria, which relied on proteolytic activity, was a predominant spoilage bacteria in stored meat under low-temperature and aerobic conditions [31]. In the meantime, _Brucella_ (5.1%), unidentified _Clostridiales_ (3.7%), _Vibrio_ (3.4%), _Lactococcus_ (3.4%), and _Enterococcus_ (3.2%) were observed in the plateau group, and _Phyllobacterium_ (8.0%), _Lactobacillus_ (3.5%), _Pseudomonas_ (3.4%), and _Brucella_ (3.1%) were observed in the mountains group. Undesirably, unidentified _Rickettsiales_ (21%), which has never been found in bacon, was one of the dominant genera in the mountains group. The genus was derived from raw meat contamination, owing to this prokaryote only  
Figure 1: Venn diagrams of the three regions based on OTUs (3% distance). Basin: 14 bacons collected from Suining, Leshan, and Chengdu; mountains: 15 bacons collected from Yibin, Ya’an, and Xichang; plateau: 10 bacons collected from Kangding and Ma’er kang.  
parasitizing eukaryotic cells [32]. Although spontaneous fermented meat products are recognized as having excellent flavor, this can sometimes give rise to poor quality products, including decreased appearance quality, a shortened shelf life, and increased health risks. For this reason, the addition of starter cultures in traditional meat products is the best way to reduce potential risk caused by microorganisms and is also the best choice for Sichuan bacon.