Induction of apoptosis in lung carcinoma cells by antiproliferative cyclic lipopeptides from marine algicolous isolate Bacillus atrophaeus strain AKLSR1

Microbes possess a vast reservoir of bioactive compounds, including cyclic lipopeptides (CLPs). In the present study, an exopolymeric biosurfactant composed of lipoheptapeptides was isolated and identified from a marine algicolous bacterial isolate, Bacillus atrophaeus strain AKLSR1, endophytic to Padina tetrastromatica. The lipopeptides were characterized by using FT-IR, NMR, GC–MS and UPLC-ESI-Q-Tof-MS/MS spectroscopic studies. Structural analysis unveiled five CLP variants that formed one major polymeric lipopeptide. These cyclic lipoheptapeptides represent a new class of surfactin family, with significant variations in the fatty acid chain length and amino acid substitutions in the peptide moiety as compared to standard lipopeptides of surfactin family. The critical micelle concentration of this biosurfactant is 0.9 mg L−1 at a surface tension of 28 mN m−1. Polymeric biosurfactant showed stable emulsification index against various organic solvents and vegetable oils. CLPs showed substantial mortality of different cancer cell lines but no toxicity towards normal human lung cell line, MRC5. Further, mechanistic studies revealed cell cycle arrest, ROS accumulation, nuclear fragmentation and cell death. Our studies indicated that CLPs induced apoptosis in lung carcinoma cell line, A549. Anti-proliferative effect of CLPs produced by marine algicolous B. atrophaeus strain AKLSR1 suggests that it could be further explored for biomedical applications.