Proteomic Analysis Explores Interactions between Lactiplantibacillus plantarum and Saccharomyces cerevisiae during Sourdough Fermentation

Abstract

Sourdough is a fermentation culture which is formed following metabolic activities of a multiple bacterial and fungal species on raw dough. However, little is known about the mechanism of interaction among different species involved in fermentation. In this study, Lactiplantibacillus plantarum Sx3 and Saccharomyces cerevisiae Sq7 were selected. Protein changes in sourdough, fermented with single culture (either Sx3 or Sq7) and mixed culture (both Sx3 and Sq7), were evaluated by proteomics. The results show that carbohydrate metabolism in mixed-culture-based sourdough is the most important metabolic pathway. A greater abundance of L-lactate dehydrogenase and UDP-glucose 4-epimerase that contribute to the quality of sourdough were observed in mixed-culture-based sourdough than those produced by a single culture. Calreticulin, enolase, seryl-tRNA synthetase, ribosomal protein L23, ribosomal protein L16, and ribosomal protein L5 that are needed for the stability of proteins were increased in mixed-culture-based sourdough. The abundance of some compounds which play an important role in enhancing the nutritional characteristics and flavour of sourdough (citrate synthase, aldehyde dehydrogenase, pyruvate decarboxylase, pyruvate dehydrogenase E1 and acetyl-CoA) was decreased. In summary, this approach provided new insights into the interaction between L. plantarum and S. cerevisiae in sourdough, which may serve as a base for further research into the detailed mechanism.

Keywords: Lactiplantibacillus plantarum; Saccharomyces cerevisiae; amino acid metabolism; carbohydrate metabolism; proteomics; sourdough.

Figure 1

Cell counts of Sx3 and Sq7 in single culture and cocultivation (A), pH of sourdough (B), TTA of sourdough (C).

Figure 2

Diversity of bacteria (A) and fungi (B) in sourdough with 0 h fermentation (Sx3_0 h_1-3) and 6 h fermentation (Control_1-3, Sx3_1-3, Sq7_1-3, Mix_1-3).

Figure 3

Whole protein function annotation.

Figure 4

String diagram of protein enrichment in carbohydrate metabolism, the left side is the protein, showing log2FC in order from top to bottom. The larger the log2FC, the greater the fold difference in the expression of upregulated proteins. The smaller the log2FC, the larger the fold difference in the downregulated protein expression. The closer log2FC is to 0, the smaller the differential expression factor of the protein; the right is the name of the KEGG pathway that enriches the target protein.

Figure 5

Glycolysis KEGG function annotation, the enzymes coloured in blue represent upregulated, in red represent downregulated enzymes according to proteomic data.

Figure 6

TCA-cycle of Mix vs Sq7, the enzymes coloured in blue represent upregulated, in red represent downregulated enzymes, in green represent the enzyme is no significant difference.

Figure 7

KEGG enrichment diagram of amino acid metabolism. The abscissa represents pathway name, and the ordinate represents enrichment rate (refers to the ratio of the protein number enriched in this pathway to the background number of the protein annotated into this pathway; the higher the ratio, the greater the degree of enrichment). The color gradient of the column represents the significance of enrichment. The deeper the default color is, the more significant the enrichment of the KEGG term is. “***” represents p < 0.001, “**” represents p < 0.01, and “*” represents p < 0.05.