Mg-fe layered double hydroxides enhance surfactin production in bacterial cells

Abstract

In this study, four additives—montmorillonite, activated carbon, and the layered double hydroxides (LDHs), Mg2 Fe–LDH and Mg2 Al–LDH—were tested for their ability to promote surfactin production in a Bacillus subtilis ATCC 21332 culture. Among these tested materials, the addition of 4 g/L of the Mg-Fe LDH, which featured an Mg/Fe molar ratio of 2:1, produced the highest surfactin yield of 5280 mg/L. During the time course of B. subtilis cultivation with the added LDH, two phases of cell growth were evident: Growth and decay. In the growth phase, the cells grew slowly and secreted a high amount of surfactin; in the decay phase, the cells degraded rapidly. The production in the presence of the Mg2 Fe–LDH had three characteristics: (i) High surfactin production at low biomass, indicating a high specific surfactin yield of 3.19 g/g DCW; (ii) rapid surfactin production within 24 h, inferring remarkably high productivity (4660 mg/L/d); and (iii) a lower carbon source flux to biomass, suggesting an efficient carbon flux to surfactin, giving a high carbon yield of 52.8%. The addition of Mg2 Fe–LDH is an effective means of enhancing surfactin production, with many potential applications and future industrial scale-up.