Fig. 5

LC-ESI–MS/MS spectrum of the surfactin precursors. a, b Surfactin precursors ion [M + H]⁺ at m/z 1008 at retention time 8.46 and 9.22 min containing a Glu1-Val2-Leu3-Val4-Asp5-Leu6-Leu/Ile7 peptide and a C14 and C15 β-hydroxy fatty acid chain, respectively. c, d Surfactin precursors ion [M + H]⁺ at m/z 1008 at retention time 8.40 and 9.16 min containing a Glu1-Val2-Leu3-Leu/Ile4-Asp5-Leu6-Val7 peptide and a C14 and C15 β-hydroxy fatty acid chain, respectively. e Surfactin precursor ions ion [M + H]⁺ at m/z 1008 at retention time 6.89 min containing a Glu1-Leu/Ile2-Leu3-Leu/Ile4-Asp5-Leu6-Leu/Ile7 peptide and a C12 β-hydroxy fatty acid chain