Abstract: This study aimed to optimize the culture conditions for Carnobacterium spp. LB1, isolated from the ribbonfish intestine, to produce anti-Pseudomonas fluorescens metabolites. By using one-factor-at-a-time method, three of the five factors were selected for their significant influences on the antibacterial activity. A Box-Behnken design was applied to evaluate the effects of interaction among the chosen variables and optimize them. The optimum culture conditions obtained were as follows: initial pH, 6.22; temperature, 28.6 ℃; and glucose concentration, 3%, where the percentage inhibition of concentrated fermentation broth harvested after 15 and 18 h against Pseudomonas fluorescens were 80.7% and 86.3%, respectively. The antibacterial mechanism was due to increased cell wall permeability and leakage of a large amount of alkaline phosphatase (AKP) after the destruction of the cell wall of Pseudomonas fluorescens, leading to metabolic disorders. Finally, the experimental results obtained under the optimized fermentation conditions were in good agreement with the model predictions, indicating that the established model in this study was feasible.

Key words: Carnobacterium spp. LB1, Pseudomonas fluorescens, antibacterial activity, response surface methodology