Using Taguchi experimental design methods to optimize trace element composition for enhanced surfactin production by Bacillus subtilis ATCC 21332

Abstract

In this work, optimizing trace element composition was attempted as a primary strategy to improve surfactin production from Bacillus subtilis ATCC 21332. Statistical experimental design (Taguchi method) was applied for the purpose of identifying optimal trace element composition in the medium. Of the five trace elements examined, Mg 2+, K +, Mn 2+, and Fe 2+ were found to be more significant factors affecting surfactin production by the B. subtilis strain. In the absence of Mg 2+ or K +, surfactin yield decreased to 0.4 g/l, which was only 25% of the value obtained from the control run. When Mn 2+ and Fe 2+ were both absent, the production yield also dropped to ca. 0.6 g/l, approximately one-third of the control value. However, when only one of the two metal ions (Fe 2+ or Mn 2+) was missing, the B. subtilis ATCC 21332 strain was able to remain over 80% of original surfactin productivity, suggesting that some interactive correlations among the selected metal ions may involve. Taguchi method was thus applied to reveal the interactive effects of Mg 2+, K +, Mn 2+, Fe 2+ on surfactin production. The results show that interaction of Mg 2+ and K + reached significant level. By further optimizing Mg 2+ and K + concentrations in the medium, the surfactin production was boosted to 3.34 g/l, which nearly doubled the yield obtained from the original control.