## 3 Results and Discussion
### Microbial Analysis  
This study used 16S rRNA gene amplicon sequencing to elucidate the effects of salt reduction on microbial diversity and abundance in cheddar cheese (Figure 2). As the salt content decreases, the Chao1, observed species, Shannon, and Simpson indices exhibit an upward trend (Figure 2A-D), indicating a gradual increase in both microbial diversity and abundance within the three cheese groups. This is due to the reduction in osmotic pressure as the salt concentration decreases, which enables microorganisms that thrive in low-salt environments to survive better and proliferate, thereby enhancing the diversity in and abundance of the microbial community [23]. The Venn diagram displays the OTU clustering in cheddar cheese (Figure 3A). Notably, the HS group exhibits the highest number of OTUs, accounting for 55.26% of the total. This suggests a high level of microbial diversity, supporting the conclusion that reduced salt content increases microbial diversity. Meanwhile, the PCoA analysis showed that the FS group and RS group were relatively close in distance, indicating their high similarity (Figure 3B).  
The genus-level heatmap (Figure 3C) and microbial taxonomy diagram (Figure 3D) revealed _Streptococcus_ and _Lactobacillus_ as the primary bacterial genera. Notably, there was no statistically significant difference between the FS group and the RS group, which aligns with the findings by [PERSON] et al. [19], who reported that a 20% reduction in sodium chloride content did not significantly alter the microbial composition of the cheese. However, in the HS group, a significant decrease in the abundance of _Streptococcus_, _Lactobacillus_, and _Carnobacterium_ was observed, accompanied by a notable increase in the abundance of _Brochotlrix_, _Pseudomonas_, and _Enterobacter_. [PERSON] et al. [23] observed that reducing the salt content inhibits the growth of _Debaryomyces hansenii_ yeast in cheese, but simultaneously enhances the growth of _Pseudomonas_ species. [PERSON] et al. [24] reported  
Figure 2: Alpha diversity analysis of three types of cheddar cheese with varying salt concentrations: Chao1 index (**A**); observed species index (**B**); Shannon index (**C**); and Simpson index (**D**) (\(\text{\textcircled{p}}<0.05\)).  
that after 30 d of cheese ripening, only _Pseudomonas_ species continued to be inhibited by salt, attributed to its relatively poor salt tolerance within the cheese environment. _Pseudomonas_ is an important spoilage bacterium in cheese, negatively impacting its sensory characteristics. For instance, certain strains belonging to this genus are capable of producing pigments [25], biogenic amines [26], and various volatile compounds [27] during the ripening process, leading to undesirable alterations in the cheese's quality and flavor. Similarly, _Enterobacter_ poses a potential contamination risk, contributing to spoilage. While _Carnobacterium_ and _Brochothorax_ are non-lactic acid bacteria involved in cheese production, their roles are still not well understood. _Streptococcus_ and _Lactobacillus_, which are common microorganisms found in cheese, possess the function of enhancing the aroma characteristics of the cheese. In conclusion, meticulous control of the salt content in cheese is crucial for regulating the microbial community structure. While a proper reduction in salt content will not significantly alter this structure, excessive reduction can shift the balance towards unfavorable microbial genera, thereby posing a risk of harmful microorganism proliferation. These findings offer valuable insights into strategies for regulating microbial community composition to enhance the shelf life of cheese.