A cyclic lipopeptide biosurfactant was separated from the culture supernatant of Bacillus subtilis HS0121 isolated in our laboratory from stratum fluids in an oil field. Its molecular structure was determined by TOF MS/MS combined with IR spectrometry, ninhydrin coloration and amino acid analyses. The experiment shows that the aliphatic chain in the cyclic lipopeptide is a β hydroxy fatty acid determined by mass spectrometry and the peptide chain consists of four Leu, one Asp, one Val and one Glu amino acids determined by amino acid analyses. The molecular weight and MS spectra of the cyclic lipopeptide were obtained by TOF MS/MS. Consequently, The length of the aliphatic chain and the sequence of amino acids in the cyclic lipopeptide before hydrolysis were directly determined according to the N rules in molecular weight, mechanism of basic cleavage, double H and single H transfer including McLafferty rearrangement. Results demonstrate that TOF MS/MS is a feasible way in determination of sequences of amino acids of lipopeptide and its corresponding structure.

Key words: biosurfactant, lipopeptide, cyclic structure, TOF MS/MS, sequence of amino acid