Exploring functional core bacteria in fermentation of a traditional Chinese food, Aspergillus-type douchi

Abstract

Douchi is a type of traditional Chinese flavoring food that has been used for thousands of years and is produced by multispecies solid-state fermentation. However, the correlation between the flavor, the microbiota, and the functional core microbiota in Aspergillus-type douchi fermentation remains unclear. In this study, Illumina MiSeq sequencing and chromatography were used to investigate the bacterial community and flavor components in Aspergillus-type douchi fermentation. The dominant phyla were Firmicutes, Proteobacteria, and Actinobacteria, and the dominant genera were Weissella, Bacillus, Anaerosalibacter, Lactobacillus, Staphylococcus, and Enterococcus. A total of 58 flavor components were detected during fermentation, including two alcohols, 14 esters, five pyrazines, three alkanes, four aldehydes, three phenols, six acids, and five other compounds. Bidirectional orthogonal partial least square modeling showed that Corynebacterium_1, Lactococcus, Atopostipes, Peptostreptococcus, norank_o__AKYG1722, Truepera, Gulosibacter, norank_f__Actinomycetaceae, and unclassified_f__Rhodobacteraceae are the functional core microbiota responsible for the formation of the flavor components during douchi fermentation. This is the first study to investigate the functional core microbiota in douchi fermentation using Illumina MiSeq sequencing and chromatographic techniques. Our findings extend our understanding of the relationships between flavor, the microbiota, and the functional core microbiota during Aspergillus-type douchi fermentation.

Fig 1. Relative abundances of bacteria at the phylum (a) and genus (b) levels during douchi fermentation.

Fig 2. Bacterial structural analysis during the douchi fermentation process.

(a) PCoA of the microbial communities, PC1 variance = 56.88%, PC2 variance = 31.82%. (b) Cluster analysis of the bacterial microbiota involved in the douchi fermentation process. Green indicates samples belonging to group 1 and red indicates samples belonging to group 2.

Fig 3. Flavor compound structural analysis during the douchi fermentation process.

(a) PCoA of flavor components generated during douchi fermentation. Green box indicates the flavor components, blue triangle indicates group 1, and red triangle denotes group 2. The grouping mode is based on Hellinger distances with 97% similarity. (b) HCA of the flavor components generated during douchi fermentation.

Fig 4. Correlation between microbiota and flavor components in the douchi fermentation process, evaluated with the O2PLS method.

(a) VIP(pred) plot of the microbiota correlated strongly with flavor components (VIP(pred) > 1.0). (b) Network of correlations between microbiota and flavor components during douchi fermentation. The left-side circle represents genera (|p| > 0.7); the right-side circle denotes flavor components; red line between microbiota and flavor components indicates positive correlation (p > 0.7); and blue line shows negative correlation (p < −0.7). (c) The details of the microbiota and the flavor components.

Fig 5. Correlations between core functional microbiota and flavor components in douchi fermentation.

The red line between microbiota and flavor components represents positive correlation (p > 0.7) and blue line indicates negative correlation (p < −0.7).