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Page 12 of 15 Lai et al. Microbiome Res Rep 2024;3:21 https://dx.doi.org/10.20517/mrr.2023.76

indicated that the metabolic state and metabolic intensity varies with microbial communities. The same
goes for the biosynthesis pathway of secondary metabolites (P < 0.01), which may affect the diversity of
flavor metabolites. The discrepancy of microbial metabolism in different environments (P < 0.01) was
probably caused by different suppliers, which were similar to the relativity between airborne
microorganisms and environmental factors of Baijiu . The biosynthesis of amino acids and cofactors
[54]
contributed to the formation of flavor precursors. In addition, the differential metabolic pathways between
samples were calculated based on LEfSe (LDA > 3, P < 0.05). As shown in Figure 4B, the pathways of
biosynthesis of secondary metabolites, amino acids, cofactors, ubiquinone, and other terpenoid-quinone,
etc., were enhanced in MF-C. Thus, the flavor precursors were significantly accumulated. The terpenoid
backbone biosynthesis was significantly dominant in MF-C, which contributed to the formation of
terpenoid flavor compounds, such as styrene, avocadene, etc. The abundant ABC transporters in MF-E
contributed to the intracellular metabolism. The starch and sucrose metabolism were active in MR-A, which
[55]
might provide sufficient substrates for ethanol fermentation .

In conclusion, results showed that the total acids and filament’s appearance varied with suppliers that
carried different microbiota. Reducing sugars, citric acid, succinic acid, and malic acid were exhausted with
fermentation. There were 809 shared metabolites identified by non-target metabolomic analysis, while no
exclusive compounds were found between samples. Queuine, cyclopentanol, pc (16:0/0:0), palmitic acid,
isorhamnetin, fisetin, and kaempferol 3-o-sophoroside were universally predominant metabolites (the
relative content > 3%) in non-salt Suancai. Metagenomic analysis showed that Lactiplantibacillus
plantarum, Leuconostoc mesenteroides, Leuconostoc lactis, Leuconostoc citreum, and Lactiplantibacillus
pentosus were the most predominant species in all samples. There were 420 differential pathways with a
significance value < 0.05 based on the Kruskal-Wallis H test. Taken as a whole, the microbial community
and its metabolism of non-salt Suancai varied with the substrates/suppliers of ingredients. This information
is practically important for the inheritance of traditional technology and quality control.

DECLARATIONS
Authors’ contributions
Methodology, software, formal analysis, investigation, writing - original draft, writing - review and editing:
Lai H
Conceptualization, methodology, formal analysis, writing - review and editing: Yan L
Methodology, formal analysis, writing - review and editing: Wang Y, Mei Y, Huang Y
Investigation, validation: Zeng X, Ge L
Methodology, validation: Zhao J, Huang Q
Resources, methodology, validation: Zhu Y
Conceptualization, methodology, writing - review and editing, supervision: Yang M
Conceptualization, writing - review and editing, supervision, project administration: Zhao N

Availability of data and materials
Not applicable.

Financial support and sponsorship
This work was financially supported by Key R&D Program of Sichuan Province (2022YFN0014 and
2022YFN0017), Sichuan Academy of Agricultural Sciences (30122-16-202301), “1 + 9” Leading Key
Scientific and Technological Research Tasks of Sichuan Academy of Agricultural Sciences (1 + 9 KJGG007),
the Open Project Program of Panxi Crops Research and Utilization Key Laboratory of Sichuan Province
(No. SZKF2214).