Studies On The Antimicrobial And Anti-tumor Activities Of Surfactin In Vitro

Biosurfactant is the hot research topic at home and abroad. In this paper, surfactin from Bacillus natto TK-1was purified via acidic precipitation, methanol extract, thin-layer chromatography (TLC) and HPLC system. Its mechanisms of antimicrobial and anti-tumor activities were studied deeply.The antimicrobial activity of surfactin was evaluated against ten microorganisms using oxford cup and liquid-fold dilution methods. Surfactin exhibited a broad spectrum of antimicrobial activity. The strongest inhibitory effect was found against Botrytis cinerea, with MIC62.5μg/mL. By observing the total sugar and protein consumption in Bacteria, surfactin can inhibit the nutrients consume of bacteria. The results of membrane permeability determination and atomic force microscopy show that showed that surfactin may be able to kill cell by breaking cell membrane. The results of stability showed that surfactin has strong antibacterial activity stability. Surfactin was tested to have strong tolerant to heat and UV light, also be steady with pH3to pH12.Surfactin inhibited proliferation of human breast cancer MCF-7cells in a dose-and time-dependent manner, with IC50at48h of27.3μg/mL. Surfactin-induced cell death was considered to be apoptotic by observing the typical apoptotic morphological change by AO/EB staining. Flow cytometric analysis also demonstrated that surfactin caused time-dependent apoptosis of MCF-7cells through cell arrest at G2/M phase. Western blotting revealed that surfactin induced accumulation of the tumour suppressor p53and cyclin kinase inhibitor p21waf1/cip1, and inhibited the activity of the G2-specific kinase, Cyclin B1/p34cdc2. Immunofluorescence and Western blotting showed that surfactin significantly suppressed the expression of vimentin, induced the α-tubulin depolymerization and rearrangement and then the skeleton system of the cells changed dramatically. The study of apoptosis signal pathway found that, surfactin caused reactive oxygen species (ROS) generation, increased the expression of p-JNK, induced the mitochondrial pathway and caspase cascade reaction.In this paper, using microbiology methods, we drawn that the antimicrobial mechanism is mainly the damage of cell membrane integrity. By cell biology methods, we drawn that Surfactin induced apoptosis through a ROS/JNK-mediated mitochondrial/caspase pathway. Specifically, surfactin caused ROS generation and ROS regulate the expression of p-JNK, and then surfactin triggered the mitochondrial/caspase apoptotic pathway indicated by enhanced Bax-to-Bcl-2expression ratio, loss of mitochondrial membrane potential, cytochrome c release, caspase cascade reaction and nuclear matrix collapses.