Enhancement of surfactin production by Bacillus velezensis NRC-1 strain using a modified bench-top bioreactor

The production of surfactin biosurfactant by Bacillus velezensis NRC -1 strain was found to be repressed by the addition of antifoaming agent which is needed to control the rapid generation of high amounts of growth associated foam. In order to overcome this problem, this study was performed in a 7.0 l bioreactor equipped with a foam collector. Maximum surfactin production of 6.3 g/l, attained at the aeration rate of 2 v/v/m, agitation speed of 300 rpm and pH of 6.8, was found to be higher than those obtained in either 250 ml flask or in a standard bioreactor in which the foam was suppressed by the addition of an antifoaming agent. It was also found that the collected foam contained certain concentrations of surfactin, fermentation medium and bacterial cells. Therefore, a recycling unit was integrated in the cultivation system design so that the generated foam was continuously collected and reintroduced into the culture medium. The results indicated that the modified bioreactor, equipped with the foam recycler produced 8.92 g/l surfactin after 28 hours of cultivation, which represent about 60% more surfactin production as compared to standard bioreactor production under similar cultivation conditions. These results correlated with the excellent results of the other kinetic parameters studied, including surfactin yield in relation to biomass (Yp/x) of 0.27 g/g, surfactin yield in relation to glucose (Yp/s) of 0.29 g/g and biomass yield in relation to glucose (Yx/s) of 1.1 g/g.