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, Mg2+, K+, Mn2+, and Fe2+ were found to be more significant factors affecting surfactin production by the B. subtilis strain. In the absence of Mg2+ or K+, surfactin yield decreased to 0.4 g/l, which was only 25% of the value obtained from the control run. When Mn2+ and Fe2+ 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 (Fe2+ or Mn2+) 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 Mg2+, K+, Mn2+, Fe2+ on surfactin production. The results show that interaction of Mg2+ and K+ reached significant level. By further optimizing Mg2+ 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. (c) 2006 Elsevier Ltd. All rights reserved.