| Summary: | The cyclic lipopeptide produced from <i>Bacillus pumilus</i> strain HY1 was isolated from Korean soybean sauce <i>cheonggukjang</i>. The chemical structures of the surfactin isomers were analyzed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). The five potential surfactin isoforms were detected with protonated masses of <i>m/z</i> 994.7, 1008.7, 1022.7, 1036.7, and 1050.7 and different structures in combination with Na<sup>+</sup>, K<sup>+</sup>, and Ca<sup>2+</sup> ions. ESI-MS/MS analysis revealed that the isolated surfactin possessed the precise amino acid sequence LLVDLL and hydroxyl fatty acids with 12 to 16 carbons. The surfactin content during c<i>heonggukjang</i> fermentation increased from 0.3 to 51.2 mg/kg over 60 h of fermentation. The mixture of five surfactin isoforms of <i>cheonggukjang</i> inhibited the growth of two cancer cell lines. The growth of both MCF-7 and Caco-2 cells was strongly inhibited with 100 μg/μL of surfactin. This study is the first-time report of five surfactin isomers of <i>Bacillus pumilus</i> strain HY1 during Korean soybean sauce <i>cheonggukjang</i> fermentation, which has cytotoxic properties.
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