Response surface methodology optimization of fermentation conditions for rapid and efficient accumulation of macrolactin A by marine Bacillus amyloliquefaciens ESB-2.

In the present work, an antibiotic-producing marine bacterium was isolated from a seawater sample collected from Yuhuan, Zhejiang, China, identified and named as Bacillus amyloliquefaciens ESB-2 on the basis of phenotypic characteristics and 16S rRNA gene sequencing. Response surface methodology was applied to optimize the fermentation conditions for rapid and efficient accumulation of macrolactin A, a pharmacologically important marine antibiotic. Eight fermentation conditions were examined for their significance on macrolactin A production using Plackett-Burman factorial design, where peptone, medium volume and temperature significantly improved production rate. Further optimization was carried out using Box-Behnken design of experiments to study the influence of process variables. The optimized fermentation condition for maximum production was peptone 14.8 mg/mL, yeast extract 1 mg/mL, FePO₄ 0.01 mg/mL, temperature 26.3 °C, initial pH value 6.0, medium volume 72.4%, rotation speed 150 r/min, inoculation 5% and fermented for 2 days. Under the optimized conditions, the concentration of macrolactin A reached 21.63 mg/L, representing a 2.4-fold increase compared to the original standard condition, which was also 17% higher than previous highest report of 18.5 mg/L and three times higher in terms of daily productivity.