Mechanism of Bacillus subtilis Y61 Promoting the Growth of Weissella: Metabolic Interaction Based on Secretion of Arginine and Isovaleric Acid

Elucidating the interactions among microbial communities in the Sichuan paocai fermentation system is of great significance for ensuring the safety and quality of paocai. In this study, the interaction between Bacillus subtilis Y61 and Weissella paramesenteroides (CWP) was preliminarily verified through the culture of CWP using the cell-free supernatant derived from Y61. Building on this, a transwell chamber was employed to spatially isolate the two bacteria. Combined with transcriptomic and metabolomic profiling, the underlying interaction mechanism was revealed. Weissella paramesenteroides (CWP) exhibited enhanced growth in the cell-free supernatant of Bacillus subtilis Y61, confirming a cross-feeding relationship between the two strains. In the transwell chamber, the promoting effect was most significant when Weissella paramesenteroides (CWP) was in the upper compartment and Bacillus subtilis Y61 in the lower compartment. Transcriptomic analysis showed that Weissella paramesenteroides (CWP) significantly upregulated genes involved in fatty acid synthesis and metabolism while downregulating those related to amino acid anabolism (p < 0.05). Metabolomic analysis further revealed that metabolites secreted by Bacillus subtilis Y61, including the key metabolites arginine and isovaleric acid, were markedly depleted during co-culture. Exogenous supplementation assays revealed that the combination of 0.1 g arginine and 2 mg isovaleric acid exhibited the strongest growth-promoting effect on Weissella paramesenteroides (CWP). Collectively, these results demonstrated that Bacillus subtilis Y61 promoted the growth of Weissella paramesenteroides (CWP) through cross-feeding via the extracellular secretion of the key metabolites arginine and isovaleric acid.