Bioreactor design for enhanced carrier-assisted surfactin production with Bacillus subtilis

Bacillus subtilis ATCC 21332 was used to produce a lipopeptide-type biosurfactant (namely, surfactin) in an innovative bioreactor tailored to solve the problems of severe foaming arising from production of the biosurfactant. To cope with the rapid foam generation, a conventional jar fermentor was integrated with a foam collector, a cell recycler, and a surfactin precipitation unit. Meanwhile, solid carriers (e.g., activated carbon) were added into the fermentation broth to increase cell mass concentration and surfactin yield. The proposed bioreactor allowed stable and efficient surfactin fermentation under intensive foaming conditions without the need of adding antifoam agents. The effect of oxygen transfer rate and mass transfer efficiency on surfactin production was also explored by employing various combinations of aeration and agitation rates. The best combination was 1.5 vvm and 300 rpm, giving an excellent maximum production rate, overall production rate, surfactin concentration, and surfactin yield of 190 mg L−1 h−1, 106 mg L−1 h−1, 6.45 g L−1, and 161 mg surfactin (g glucose)−1, respectively. It was also found that the oxygen volumetric mass transfer coefficient (KLa) was highly correlated with the performance of surfactin production. The highest surfactin productivity was achieved when the fermentation was carried out at a KLa value of 0.0132 s−1.