Abstract:Paenibacillus thiaminolyticus SY20 is an antimicrobial strain isolated from acid bamboo shoots in Zhangzhou, Fujian. Previous studies have demonstrated that this species can produce a rare lipopeptide antimicrobial substance, polymyxin A1. To improve the ability of P. thiaminolyticus to produce antimicrobial substances, the active strain was used as the research object, and the antimicrobial diameters against Escherichia coli were used as the investigation index to optimize the fermentation conditions. Single-factor experiments were conducted to evaluate the effects of different carbon sources, nitrogen sources, and inorganic salt types and their concentrations on the production of antimicrobial substances. The three significant factors, namely ammonium phosphate, KCl, and NaCl, were screened and further analyzed using the Plackett-Burman method. The optimal medium combination was determined using a Box–Behnken central composite design. Finally, the inoculation volume, pH value, fermentation time and temperature were optimized to obtain the most effective fermentation conditions, which were then verified experimentally. The results showed that the optimum fermentation medium for producing antimicrobial substances in P. thiaminolyticus SY20 was composed of 20 g/L maltose, 15 g/L cottonseed cake flour, 8 g/L (NH4)2HPO4, 10 g/L KCl, and 10 g/L NaCl. The optimized fermentation conditions were as follows: pH 7.5, fermentation temperature of 28 ℃ , and fermentation time of 60 h. After optimization, the inhibition diameter of the fermented supernatant was 22.8 mm, which was 1.5-fold larger than that before optimization (15.2 mm). The ability of the strain to produce antimicrobial substances was significantly improved, providing a foundation for large-scale isolation and purification of the antibacterial substances.
