Application of response-surface methodology to evaluate the optimum medium components for the enhanced production of lichenysin by Bacillus licheniformis R2

Biosurfactants have gained attention because they exhibit some advantages such as biodegradability, low toxicity, ecological acceptability and ability to be produced from renewable and cheaper substrates. They are widely used for environmental applications for bioremediation and also in biomedical field. However, the high cost of production is the limiting factor for widespread industrial applications. Thus, optimization of the growth medium for biosurfactant-lichenysin production by Bacillus licheniformis R2 was carried out using response-surface methodology. A preliminary screening phase based on a two-level fractional factorial design led to the identification of NH₄NO₃, glucose, Na₂HPO₄ and MnSO₄·4H₂O concentrations as the most significant variables affecting the fermentation process. The 2⁴ full-factorial central composite design was then applied to further optimize the biosurfactant production. The optimal levels of the aforementioned variables were (g/l): NH₄NO₃, 1.0; glucose, 34.0; KH₂PO₄, 6.0; Na₂HPO₄, 2.7; MgSO₄·7H₂O, 0.1; CaCl₂, 1.2 × 10^-3; FeSO₄·7H₂O, 1.65 × 10^-3; MnSO₄·4H₂O, 1.5 × 10^-3 and Na-EDTA, 2.2 × 10^-3. With the optimization procedure, the relative lichenysin yield expressed as the critical micelle dilution (CMD) was fourfold higher than that obtained in the non-optimized reference medium.