A new surfactin-C17 produced by Bacillus subtilis TD7 with a low critical micelle concentration and high biological activity

Abstract

A new member of the surfactin family of microbial lipopeptides has been isolated from the cell broth of Bacillus subtilis TD7 using a combination of organic solvent extraction and RP-HPLC, and its primary chemical structure was determined by ESI-MS, LC-MS/MS, GC-MS, ¹H-NMR, ¹³C-NMR and amino acid analysis. The surfactin-C₁₇ consists of a β-hydroxy heptadecanoic acid chain and a heptapeptide ring with the sequence of N–Glu–Leu–Leu–Val–Asp–Leu–Leu–C, which is a new member with the longest hydrophobic chain in the surfactin family produced by B. subtilis. Compared with the reported members of surfactins-C_11∼16, surfactin-C₁₇ showed a very low critical micelle concentration (CMC) of 4.02 × 10⁻⁶ mol L⁻¹ in 10 mM PBS at 25 °C, and a very low surface tension of 28.98 mN m⁻¹ at CMC (γ_CMC); meanwhile, it inherited a strong antibacterial activity against the Gram-positive Micrococcus luteus with a MIC value of 60 mg L⁻¹, and a higher hemolytic activity on sheep erythrocytes. This work concluded that increasing the hydrophobic chain length of a surfactin certainly contributed to decreasing its CMC and would facilitate the development of environmentally friendly biosurfactants and extend the domain of surfactin biosurfactants to new applications such as in pharmaceutical, bioremediation and detergent industries.