Identification and characterization of a surfactin from Pseudomonas gessardii: A symbiotic bacterium with potent anticancer activity

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Prasiola japonica, traditionally used as food and folk medicine in South Korea, exerts pharmacological properties, including antioxidant, anti-inflammatory, antidiabetic, and anticancer effects. In this study, we explored symbiotic microbes associated with P. japonica and identified Pseudomonas gessardii as a nonpathogenic symbiotic bacterium through 16 S rDNA sequencing. Bioactivity-guided fractionation of P. gessardii ethanol extracts, utilizing a series of non-polar to polar solvents, led to the isolation of a single bioactive compound (SF10) from the ethyl acetate fraction. Structural analysis using LC-MS and NMR spectroscopy identified SF10 as surfactin C15, a lipopeptide consisting of 7 amino acids and a β-hydroxy fatty acid chain containing 15 carbon atoms. This represents the first discovery of surfactin production in P. gessardii, expanding known surfactin-producing genera beyond Bacillus. In HT-29 colorectal cancer cells, surfactin C15 demonstrated significant anticancer activity through multiple mechanisms: inhibition of cancer stem cell marker CD133 expression, upregulation of pro-apoptotic factors (CHOP, PUMA, DR5), and modulation of cell cycle regulators (CDKN1A,CCNE1, CDK5). Furthermore, surfactin C15 induced necrotic cell death, confirmed by increased lactate dehydrogenase release and flow cytometry analysis showing dose-dependent increases in necrotic cell populations. This study reveals a novel source of surfactin with unique cancer cell-targeting properties, particularly through its ability to induce necrosis in colorectal cancer cells, suggesting potential therapeutic applications in cancer treatment.