Optimization of the enrichment medium for recombinant ChIL-4-ChIL-2 in Lactococcus lactis through response surface methodology

Coccidiosis, caused by Eimeria, represents a significant challenge to the poultry industry and leads to significant economic losses to the poultry industry. Traditional anticoccidial drugs is diminishing due to drug resistance, and although live vaccines are an effective preventive and treatment means, they may cause mild infections and affect weight gain when used. Recombinant ChIL-4-ChIL-2 in Lactococcus lactis, as a new type of food-grade recombinant cytokine immunoadjuvant, characterized by its ability to enhance the immunological efficacy of live vaccines against chicken coccidiosis. In this study, using the OD₆₀₀ value of the culture broth of ChIL-4-ChIL-2 in Lactococcus lactis as the index, the optimal combination of carbon and nitrogen sources and inorganic salts in the medium was determined through single-factor experiments, and the medium formula was optimized using Box-Behnken design and response surface analysis. The results of single-factor experiments indicated that the optimal carbon source, nitrogen source, and buffer salt addition amounts in the M17 medium for recombinant ChIL-4-ChIL-2 in Lactococcus lactis were as follows: 1 % mixed carbon source (with a trehalose to glucose ratio of 1:1), 7 % yeast extract powder as the nitrogen source, and 0.5 % potassium dihydrogen phosphate-sodium hydroxide as the buffer salt. Furthermore, the results of response surface methodology experiments indicate that the optimal medium formulation for recombinant ChIL-4-ChIL-2 in Lactococcus lactis is M17 medium supplemented with 1 % carbon source (glucose: trehalose = 1:1), 8 % nitrogen source (yeast extract powder), and 0.8 % buffer salts (potassium dihydrogen phosphate-sodium hydroxide). This optimized medium can significantly increase the yield of recombinant ChIL-4-ChIL-2 in Lactococcus lactis, and the OD₆₀₀ value of the cell density can reach 1.103. This optimized medium provides a scientific foundation for developing a production process aimed at the large-scale production of recombinant ChIL-4-ChIL-2 in Lactococcus lactis.