Evaluation of Yield and Surface Tension-lowering Activity of Iturin A Produced by Bacillus subtilis RB14

Bacillus subtilis RB14 produces the lipopeptide antibiotic iturin A by submerged and biofilm fermentation. In this study, we optimized the conditions for iturin A production in a jar fermentor. The maximum yield of iturin A was 932 mg L^-1 after 120 h. The surface tension of water decreased from 72.0 to 39.0 mN m^-1 as the concentrations of C₁₄ iturin A increased, indicating that C₁₄ iturin A behaves as a surfactant in water. The critical micellar concentration obtained from the intersection of two fitted lines was 1.2 × 10^-4 M. Moreover, the surface tension of water decreased as the length of the alkyl chain of iturin A increased.