An optimal carbon source can enhance the Paracin 1.7 titer and reduce carbon source consumption in cocultures of Lacticaseibacillus paracasei HD1.7 and Bacillus spp.

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The low yield of bacteriocins limits their industrial use, and optimization of inoculation conditions and carbon sources (CS) are good strategies for improvement. In a previous study, we established three coculture systems of Lacticaseibacillus paracasei HD1.7 with Bacillus spp. Optimization of the inoculation conditions effectively increased the Paracin 1.7 titer. This study focused on the effects of the carbon source type (TCS) and carbon source concentration (CSC) on fermentation characteristics and bacteriocin titers. The results showed that the optimal TCS for bacteriocin production by different strain combinations is strain-specific. Adjusting the CS resulted in a higher Paracin 1.7 titer with less CS consumption. The B. subtilis group saved substrate consumption while yielding more Paracin 1.7 when 1T Glc was used as the CS. The optimal CS for the B. licheniformis group was 2T Fru. The B. pumilus group had the highest titer at 1T Fru. Gene expression analysis revealed that the appropriate TCS upregulated the relative expression levels of transmembrane protein genes ( ptsG , fruA ) and population sensing-related genes ( prcK , prcR , and luxS ), facilitating nutrient transport and information exchange. Structural equation modeling confirmed that controlling the CS can influence microbial growth and thus CS consumption, ultimately obtaining a satisfactory bacteriocin titer. • The CS consumption and bacterial growth can be adjusted by controlling the CS. • Optimal TCS for bacteriocin production by different systems is strain-specific. • Bsub group can conserve CS while obtaining a higher Paracin1.7 when 1T Glc is CS. • The Bpum group could obtain the highest Paracin1.7 titer at 1T Fru as CS. • Optimal TCS up-regulates the expression of ptsG , fruA , prcK , prcR , and luxS.