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Page 10 of 15 Lai et al. Microbiome Res Rep 2024;3:21 https://dx.doi.org/10.20517/mrr.2023.76

Figure 3. (A) Microbial composition of samples at genus level; (B) Heatmap of the microbial community at the species level. Microbes
were determined with three parallels, and the relative abundance of the genus was taken as the average. The top fifty species by relative
abundance were shown in the heatmap.

[41]
metabolic state and mainly regulate amino acid, lipid, and nucleotide metabolism pathways . More
importantly, Lactobacillus can counteract the combinational coldness and acidity by increasing the
biosynthesis of several important biomolecules such as glycolipids and glycoproteins through
[42]
metabolism . It could be inferred that abundant Lactobacillus ensures normal fermentation of a product
because the coldness and acidity situation is also maintained in non-salt Suancai. Leuconostoc is often
considered a flavor producer and occupies an important place in MF-C (82.49%). Interestingly, Weissella
[43]
abundance was highest in MF-A, which can drive the diversity and dynamics of the microbial community
during fermentation. It helps in the process by its involvement in the transportation and metabolism of
amino acids and carbohydrates . In addition, Lactococcus was involved in the events of low temperature
[44]
and a series of metabolic reactions through generated proteins , which could support the normal
[45]
fermentation of non-salt Suancai in extreme environments as well, which was highlighted in MF-B, -C, and
-D. There was 2.15% Pseudomonas in growth in MF-B, which showed a capability to generate 1-octen-3-ol
[46]
and was associated with ketone production .
Furthermore, as shown in Figure 3B, metagenomic analysis could anchor microbial species.
Lactiplantibacillus plantarum, Leuconostoc mesenteroides, Leuconostoc lactis, Leuconostoc citreum, and
Lactiplantibacillus pentosus were predominant species in all samples. Among them, L. plantarum was the
most common species in non-salt Suancai, which is also considered a probiotic to attenuate oxidative stress
in neuroblastoma cells . Annotations of metabolic pathways suggested that the probiotic L. plantarum
[47]
[48]
could alleviate intestinal ischemia-reperfusion damage by modulating calcium-phosphorus homeostasis .
In addition, the application of Ln. mesenteroides increased conjugated linoleic acid and improved the
safety . In particular, some abundant but unclassified species were identified in the top 50 species,
[49]
suggesting that there are many unconventional species in non-salt Suancai. Clustering analysis showed that
MF-B and MF-C were classified into an identical cluster as a relatively low abundance of L. plantarum.
Meanwhile, both samples showed lower lactic acid accumulation, which demonstrated that both
fermentation mechanisms were different to other samples and related to L. plantarum abundance.
Ln. pseudomesenteroides showed the highest abundance in MF-C, which usually possess the ability to
produce exopolysaccharides that might relate to sugar filament appearance.
[50]