Enhanced Production of Surfactin by Bacillus subtilis E8 Mutant Obtained by Ion Beam Implantation

The application of surfactin is hampered by its high production cost. In this study, a high-producing surfactin mutant obtained by ion beam implantation, Bacillus subtilis E8, has been used to produce surfactin. The production in a modified bioreactor and the properties of the surfactin produced by the mutant strain have been investigated. The results indicate that the modified bioreactor with a cell/foam recycler showed an advantage as compared to a simple reactor. The concentration of crude surfactin (including recovery from two parts of foam and broth fractionation) increased significantly from 0.75 to 10.26 g/L. Time course profiles showed that surfactin produced by B. subtilis E8 was growth-associated during the exponential phase of biomass, and the growth-associated product formation constant (α) was 894 mg per g of dry cell (R^2=0.918). The concentration of crude surfactin and biomass reached a maximum (12.20 and 6.50 g/L) after cultivation for about 32 h. The crude and extracted surfactin (critical micelle concentrations were 15 and 13 μM, respectively) exhibited excellent emulsification property, pH stability, thermal stability and resistance to salts, which widens its potential application.