Production and MS-MS analysis of new fluorinated surfactins from a Chinese Bacillus subtilis isolate

Abstract Supplementation of the culture medium of a Bacillus subtilis strain with 5,5,5-trifluoroleucine resulted in the production of modified surfactins. Products were characterized by 19F NMR and LC-MS/MS, confirming fluorinated leucine could be incorporated in place of any of the four leucine residues present in native surfactins, with the Leu1 and Leu2 positions incorporating a higher percentage of the modified amino acids. However, analysis of the culture supernatant showed that a significant amount (0.5 mg/ml) trifluoroleucine was not metabolized and retained in the supernatant and methanolic extract; further, MS and HPLC analysis indicated that some of the trifluoroleucine had also undergone deamination and reduction reactions to yield 5,5,5-trifluoro-2-hydroxy-4-methylpentanoic acid as the major product (0.25 mg/1.0 mg trifluoroleucine).