Cost-Effective Production of Surfactin from Xylose-Rich Corncob Hydrolysate Using Bacillus subtilis BS-37

Purpose: Corncob hydrolysate, feather hydrolysate waste (FHW) and glutamate mill waste (GMW) are inexpensive raw materials derived from agricultural waste biomass. The aim of the study was to optimize the production of surfactin from the xylose-rich corncob hydrolysate and low-cost residues rich in organic nitrogen using Bacillus subtilis BS-37. Methods: Hydrolysis of corncob was carried out with 1.5% H₂SO₄, FHW or GMW was used as nitrogen source to produce surfactin. Sugar compositions of corncob hydrolysate and surfactin titer were determined by HPLC. The dry weight method was used to measure biomass in fermentation broth. Results: We discovered that the efficient surfactin producer B. subtilis BS-37 can use xylose as sole carbon source, but the addition of organic nitrogen sources was essential for surfactin production. Consequently, the xylose-rich corncob hydrolysate and low-cost residues rich in organic nitrogen were used to produce surfactin. Strain BS-37 was able to tolerate significant concentrations of several inhibitory compounds found in corncob hydrolysate, whereby acetic acid even enhanced surfactin production. Furthermore, NaOH-neutralized corncob hydrolysate was more suitable for surfactin production than the traditional Ca(OH)₂-neutralized feedstock. Conclusions: We achieved a maximal surfactin yield of 523 mg/L from NaOH-neutralized corncob hydrolysate and feather hydrolysate waste. Furthermore, the product contained 55.3% of the most desirable surfactin isoform C₁₅. To our best knowledge, this is the first report of surfactin production with xylose as the main fermentable carbon source.