Surfactin and poly–γ–glutamic acid co–production by Bacillus velezensis P#02 using a corn steep liquor–based medium

Bacillus velezensis P#02 simultaneously produced surfactin and poly–γ–glutamic acid (γ–PGA). Among the different culture media studied, the one containing corn steep liquor (100 mL/L), glucose (10 g/L), and glutamic acid (10 g/L) as sole ingredients (CSL–G–Glut(10)) offered the best results regarding biosurfactant and biopolymer production. Although biosurfactant production occurred both under shaking and static conditions, significant biopolymer production occurred only in static cultures. Using the culture medium CSL–G–Glut(10), 910 ± 20 mg surfactin/L and 9.8 ± 0.2 g γ–PGA/L were produced. Surfactin was synthetized as a mixture of five different homologues (fatty acid chains ranging between C12 and C16), being the most abundant C14– and C15–surfactin. Surfactin reduced the surface tension up to 29 mN/m, with a critical micelle concentration of 52 mg/L, and exhibited a significant emulsifying activity. B. velezensis P#02 γ–PGA, which molecular weight was around 229 kDa, displayed a non–Newtonian shear–thinning profile, achieving apparent viscosity values around 3800 mPa s in aqueous solution, with a predominant viscous behavior. Accordingly, B. velezensis P#02 is a promising strain for the simultaneous production of γ–PGA and surfactin using the waste stream corn steep liquor.